Publications by authors named "Susanna A Wood"

106 Publications

Cryoprotectant treatment tests on three morphologically diverse marine dinoflagellates and the cryopreservation of Breviolum sp. (Symbiodiniaceae).

Sci Rep 2022 Jan 13;12(1):646. Epub 2022 Jan 13.

School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, 6140, New Zealand.

Dinoflagellates are among the most diverse group of microalgae. Many dinoflagellate species have been isolated and cultured, and these are used for scientific, industrial, pharmaceutical, and agricultural applications. Maintaining cultures is time-consuming, expensive, and there is a risk of contamination or genetic drift. Cryopreservation offers an efficient means for their long-term preservation. Cryopreservation of larger dinoflagellate species is challenging and to date there has been only limited success. In this study, we explored the effect of cryoprotectant agents (CPAs) and freezing methods on three species: Vulcanodinium rugosum, Alexandrium pacificum and Breviolum sp. A total of 12 CPAs were assessed at concentrations between 5 and 15%, as well as in combination with dimethyl sulfoxide (DMSO) and other non-penetrating CPAs. Two freezing techniques were employed: rapid freezing and controlled-rate freezing. Breviolum sp. was successfully cryopreserved using 15% DMSO. Despite exploring different CPAs and optimizing the freezing techniques, we were unable to successfully cryopreserve V. rugosum and A. pacificum. For Breviolum sp. there was higher cell viability (45.4 ± 2.2%) when using the controlled-rate freezing compared to the rapid freezing technique (10.0 ± 2.8%). This optimized cryopreservation protocol will be of benefit for the cryopreservation of other species from the family Symbiodiniaceae.
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http://dx.doi.org/10.1038/s41598-021-04227-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8758677PMC
January 2022

Growth at the limits: comparing trace metal limitation of a freshwater cyanobacterium (Dolichospermum lemmermannii) and a freshwater diatom (Fragilaria crotonensis).

Sci Rep 2022 Jan 10;12(1):467. Epub 2022 Jan 10.

Cawthron Institute, Nelson, 7010, New Zealand.

Freshwater phytoplankton blooms are increasing in prevalence and there are conflicting views on whether trace metals limit growth of key species and thus bloom formation. The Taupō Volcanic Zone (TVZ), New Zealand, was formed by multiple eruptions of a super-volcano which emitted rhyolitic tephra leaving lakes depleted in trace metals. This provides an opportunity to test the potential of trace metal limitation on freshwater phytoplankton growth under nanomolar concentrations. Growth responses of two algal species isolated from Lake Taupō, Dolichospermum lemmermannii (cyanobacteria) and Fragilaria crotonensis (diatom), to six biologically important trace metals (manganese, iron, zinc, cobalt, copper and molybdenum) were examined in culture experiments. These were conducted at three trace metal concentrations: (1) ambient, (2) two-times ambient, and (3) ten-times ambient concentrations in Lake Taupō. Elevated concentrations of iron significantly increased growth rates and maximum cell densities in D. lemmermannii, whereas no significant concentration dependence was observed for other trace metals. Fragilaria crotonensis showed no significant growth response to elevated concentrations of trace metals. These results highlight the importance of iron as a growth limiting nutrient for cyanobacteria and indicate that even small (twofold) increases in Fe concentrations could enhance cyanobacteria growth rates in Lake Taupō, potentially causing cyanobacterial blooms.
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http://dx.doi.org/10.1038/s41598-021-04533-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8748459PMC
January 2022

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation.

Freshw Biol 2020 Oct;65(10):1824-1842

Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America.

1. This review summarises knowledge on the ecology, toxin production, and impacts of toxic freshwater benthic cyanobacterial proliferations. It documents monitoring, management, and sampling strategies, and explores mitigation options. 2. Toxic proliferations of freshwater benthic cyanobacteria (taxa that grow attached to substrates) occur in streams, rivers, lakes, and thermal and meltwater ponds, and have been reported in 19 countries. Anatoxin- and microcystin-containing mats are most commonly reported (eight and 10 countries, respectively). 3. Studies exploring factors that promote toxic benthic cyanobacterial proliferations are limited to a few species and habitats. There is a hierarchy of importance in environmental and biological factors that regulate proliferations with variables such as flow (rivers), fine sediment deposition, nutrients, associated microbes, and grazing identified as key drivers. Regulating factors differ among colonisation, expansion, and dispersal phases. 4. New -omics-based approaches are providing novel insights into the physiological attributes of benthic cyanobacteria and the role of associated microorganisms in facilitating their proliferation. 5. Proliferations are commonly comprised of both toxic and non-toxic strains, and the relative proportion of these is the key factor contributing to the overall toxin content of each mat. 6. While these events are becoming more commonly reported globally, we currently lack standardised approaches to detect, monitor, and manage this emerging health issue. To solve these critical gaps, global collaborations are needed to facilitate the rapid transfer of knowledge and promote the development of standardised techniques that can be applied to diverse habitats and species, and ultimately lead to improved management.
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http://dx.doi.org/10.1111/fwb.13532DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8715960PMC
October 2020

A bacterial index to estimate lake trophic level: National scale validation.

Sci Total Environ 2021 Dec 21;812:152385. Epub 2021 Dec 21.

Victoria University of Wellington, PO Box 600, Wellington 6012, New Zealand.

Lakes and their catchments have been subjected to centuries to millennia of exploitation by humans. Efficient monitoring methods are required to promote proactive protection and management. Traditional monitoring is time consuming and expensive, which limits the number of lakes monitored. Lake surface sediments provide a temporally integrated representation of environmental conditions and contain high microbial biomass. Based on these attributes, we hypothesized that bacteria associated with lake trophic states could be identified and used to develop an index that would not be confounded by non-nutrient stressor gradients. Metabarcoding (16S rRNA gene) was used to assess bacterial communities present in surface sediments from 259 non-saline lakes in New Zealand encompassing a range of trophic states from alpine microtrophic lakes to lowland hypertrophic lakes. A subset of lakes (n = 96) with monitoring data was used to identify indicator amplicon sequence variants (ASVs) associated with different trophic states. A total of 10,888 indicator taxa were identified and used to develop a Sediment Bacterial Trophic Index (SBTI), which signficantly correlated (r = 0.842, P < 0.001) with the Trophic Lake Index. The SBTI was then derived for the remaining 163 lakes, providing new knowledge of the trophic state of these unmonitored lakes. This new, robust DNA-based tool provides a rapid and cost-effective method that will allow a greater number of lakes to be monitored and more effectively managed in New Zealand and globally. The SBTI could also be applied in a paleolimnological context to investigate changes in trophic status over centuries to millennia.
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http://dx.doi.org/10.1016/j.scitotenv.2021.152385DOI Listing
December 2021

Metabarcoding Reveals Lacustrine Picocyanobacteria Respond to Environmental Change Through Adaptive Community Structuring.

Front Microbiol 2021 12;12:757929. Epub 2021 Nov 12.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Picocyanobacteria (Pcy) are important yet understudied components of lake foodwebs. While phylogenetic studies of isolated strains reveal a high diversity of freshwater genotypes, little is known about abiotic drivers associated with Pcy in different lakes. Due to methodological limitations, most previous studies assess potential drivers using total cell abundances as a response, with often conflicting and inconsistent results. In the present study, we explored how picocyanobacterial communities respond to environmental change using a combination of epifluorescence microscopy and community data determined using 16S rRNA gene metabarcoding. Temporal shifts in picocyanobacterial abundance, diversity and community dynamics were assessed in relation to potential environmental drivers in five contrasting lakes over 1year. Cell abundances alone were not consistently related to environmental variables across lakes. However, the addition of metabarcoding data revealed diverse picocyanobacterial communities that differed significantly between lakes, driven by environmental variables related to trophic state. Within each lake, communities were temporally dynamic and certain amplicon sequence variants (ASVs) were strongly associated with specific environmental drivers. Rapid shifts in community structure and composition were often related to environmental changes, indicating that lacustrine Pcy can persist at high abundances through collective community adaptation. These results demonstrate that a combination of microscopy and metabarcoding enables an in-depth characterisation of picocyanobacterial communities and reveals strain-specific drivers. We recommend that future studies cease referring to picocyanobacterial as one functional group and take strain specific variability into consideration.
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http://dx.doi.org/10.3389/fmicb.2021.757929DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8633389PMC
November 2021

Winter diet of Japanese macaques from Chubu Sangaku National Park, Japan incorporates freshwater biota.

Sci Rep 2021 11 29;11(1):23091. Epub 2021 Nov 29.

Department of Biology, Faculty of Science, Shinshu University, Matsumoto, Japan.

The Japanese macaque (Macaca fuscata) is native to the main islands of Japan, except Hokkaido, and is the most northerly living non-human primate. In the Chubu Sangaku National Park of the Japanese Alps, macaques live in one of the coldest areas of the world, with snow cover limiting the availability of preferred food sources. Winter is typically a bottleneck for food availability potentially resulting in marked energy deficits, and mortality may result from famine. However, streams with groundwater upwelling flow during the winter with a constant water temperature of about 5 °C are easily accessible for Japanese macaques to search for riverine biota. We used metabarcoding (Cytochrome c oxidase I) of fecal samples from Japanese macaques to determine their wintertime diet. Here we provide the first robust evidence that Japanese macaques feed on freshwater biota, including brown trout, riverine insects and molluscs, in Chubu Sangaku National Park. These additional food sources likely aid their winter survival.
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http://dx.doi.org/10.1038/s41598-021-01972-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8629975PMC
November 2021

Genome Streamlining, Plasticity, and Metabolic Versatility Distinguish Co-occurring Toxic and Nontoxic Cyanobacterial Strains of .

mBio 2021 10 26;12(5):e0223521. Epub 2021 Oct 26.

School of Biological Sciences, The University of Aucklandgrid.9654.e, Auckland, New Zealand.

Harmful cyanobacterial bloom occurrences have increased worldwide due to climate change and eutrophication, causing nuisance and animal deaths. Species from the benthic cyanobacterial genus are ubiquitous and form thick mats in freshwater systems, such as rivers, that are sometimes toxic due to the production of potent neurotoxins (anatoxins). Anatoxin-producing (toxic) strains typically coexist with non-anatoxin-producing (nontoxic) strains in mats, although the reason for this is unclear. To determine the genetic mechanisms differentiating toxic and nontoxic , we sequenced and assembled genomes from 11 cultures and compared these to another 31 genomes. Average nucleotide identities (ANI) indicate that toxic and nontoxic strains are distinct species (ANI, <95%), and only 6% of genes are shared across all 42 genomes, suggesting a high level of genetic divergence among strains. Comparative genomics showed substantial genome streamlining in toxic strains and a potential dependency on external sources for thiamine and sucrose. Toxic and nontoxic strains are further differentiated by an additional set of putative nitrate transporter (nitrogen uptake) and cyanophycin (carbon and nitrogen storage) genes, respectively. These genes likely confer distinct competitive advantages based on nutrient availability and suggest nontoxic strains are more robust to nutrient fluctuations. Nontoxic strains also possess twice as many transposable elements, potentially facilitating greater genetic adaptation to environmental changes. Our results offer insights into the divergent evolution of strains and the potential for cooperative and competitive interactions that contribute to the co-occurrence of toxic and nontoxic species within mats. Microcoleus autumnalis, and closely related species, compose a geographically widespread group of freshwater benthic cyanobacteria. Canine deaths due to anatoxin-a poisoning, following exposure to toxic proliferations, have been reported globally. While proliferations are on the rise, the mechanisms underpinning competition between, or coexistence of, toxic and nontoxic strains are unknown. This study identifies substantial genetic differences between anatoxin-producing and non-anatoxin-producing strains, pointing to reduced metabolic flexibility in toxic strains, and potential dependence on cohabiting nontoxic strains. Results provide insights into the metabolic and evolutionary differences between toxic and nontoxic , which may assist in predicting and managing aquatic proliferations.
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http://dx.doi.org/10.1128/mBio.02235-21DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8546630PMC
October 2021

Development of droplet digital Polymerase Chain Reaction assays for the detection of long-finned () and short-finned () eels in environmental samples.

PeerJ 2021 27;9:e12157. Epub 2021 Sep 27.

Cawthron Institute, Nelson, New Zealand.

Freshwater eels are ecologically, and culturally important worldwide. The New Zealand long-finned eel () and short-finned eel () are apex predators, playing an important role in ecosystem functioning of rivers and lakes. Recently, there has been a national decline in their populations due to habitat destruction and commercial harvest. The emergence of targeted environmental DNA detection methodologies provides an opportunity to enhance information about their past and present distributions. In this study we successfully developed species-specific droplet digital Polymerase Chain Reaction (ddPCR) assays to detect and DNA in water and sediment samples. Assays utilized primers and probes designed for regions of the mitochondrial cytochrome b and 16S ribosomal RNA genes in and , respectively. River water samples ( = 27) were analyzed using metabarcoding of fish taxa and were compared with the ddPCR assays. The presence of and DNA was detected in a greater number of water samples using ddPCR in comparison to metabarcoding. There was a strong and positive correlation between gene copies (ddPCR analyses) and relative eel sequence reads (metabarcoding analyses) when compared to eel biomass. These ddPCR assays provide a new method for assessing spatial distributions of and in a range of environments and sample types.
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http://dx.doi.org/10.7717/peerj.12157DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8483004PMC
September 2021

Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide.

Bioscience 2021 Oct 7;71(10):1011-1027. Epub 2021 Jul 7.

Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan.

Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes associated with nutrient pollution in groundwater, but complex changes in climate, nutrient transport, lake hydrodynamics, and food web structure may also facilitate this emerging threat to clear lakes. A coordinated effort among members of the public, managers, and scientists is needed to document the occurrence of FABs, to standardize methods for measuring their severity, to adapt existing data collection networks to include nearshore habitats, and to mitigate and reverse this profound structural change in lake ecosystems. Current models of lake eutrophication do not explain this littoral greening. However, a cohesive response to it is essential for protecting some of the world's most valued lakes and the flora, fauna, and ecosystem services they sustain.
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http://dx.doi.org/10.1093/biosci/biab049DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8490932PMC
October 2021

Deciphering the molecular signal from past and alive bacterial communities in aquatic sedimentary archives.

Mol Ecol Resour 2021 Sep 25. Epub 2021 Sep 25.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Lake sediments accumulate information on biological communities thus acting as natural archives. Traditionally paleolimnology has focussed on fossilized remains of organisms, however, many organisms do not leave fossil evidence, meaning major ecosystem components are missing from environmental reconstructions. Many paleolimnology studies now incorporate molecular methods, including investigating microbial communities using environmental DNA (eDNA), but there is uncertainty about the contribution of living organisms to molecular inventories. In the present study, we obtained DNA and RNA inventories from sediment spanning 700 years to investigate the contribution of past and active communities to the molecular signal from sedimentary archives. Additionally, a droplet digital PCR (ddPCR) targeting the 16S ribosomal RNA (16S rRNA) gene of the photosynthetic cyanobacterial genera Microcystis was used to explore if RNA signals were from legacy RNA. We posit that the RNA signal is a mixture of legacy RNA, dormant cells, living bacteria and modern-day trace level contaminants that were introduced during sampling and preferentially amplified. The presence of legacy RNA was confirmed by the detection of Microcystis in sediments aged to ~200 years ago. Recent comparisons between 16S rRNA gene metabarcoding and traditional paleo proxies showed that past changes in bacterial communities can be reconstructed from sedimentary archives. The recovery of RNA in the present study has provided new insights into the origin of these signals. However, caution is required during analysis and interpretation of 16S rRNA gene metabarcoding data especially in recent sediments were there are potentially active bacteria.
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http://dx.doi.org/10.1111/1755-0998.13515DOI Listing
September 2021

Towards reproducible metabarcoding data: Lessons from an international cross-laboratory experiment.

Mol Ecol Resour 2022 Feb 31;22(2):519-538. Epub 2021 Aug 31.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Advances in high-throughput sequencing (HTS) are revolutionizing monitoring in marine environments by enabling rapid, accurate and holistic detection of species within complex biological samples. Research institutions worldwide increasingly employ HTS methods for biodiversity assessments. However, variance in laboratory procedures, analytical workflows and bioinformatic pipelines impede the transferability and comparability of results across research groups. An international experiment was conducted to assess the consistency of metabarcoding results derived from identical samples and primer sets using varying laboratory procedures. Homogenized biofouling samples collected from four coastal locations (Australia, Canada, New Zealand and the USA) were distributed to 12 independent laboratories. Participants were asked to follow one of two HTS library preparation workflows. While DNA extraction, primers and bioinformatic analyses were purposefully standardized to allow comparison, many other technical variables were allowed to vary among laboratories (amplification protocols, type of instrument used, etc.). Despite substantial variation observed in raw results, the primary signal in the data was consistent, with the samples grouping strongly by geographical origin for all data sets. Simple post hoc data clean-up by removing low-quality samples gave the best improvement in sample classification for nuclear 18S rRNA gene data, with an overall 92.81% correct group attribution. For mitochondrial COI gene data, the best classification result (95.58%) was achieved after correction for contamination errors. The identified critical methodological factors that introduced the greatest variability (preservation buffer, sample defrosting, template concentration, DNA polymerase, PCR enhancer) should be of great assistance in standardizing future biodiversity studies using metabarcoding.
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http://dx.doi.org/10.1111/1755-0998.13485DOI Listing
February 2022

Lake microbial communities are not resistant or resilient to repeated large-scale natural pulse disturbances.

Mol Ecol 2021 10 22;30(20):5137-5150. Epub 2021 Aug 22.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Opportunities to study community-level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well-resolved sediment pulses, triggered by earthquakes. These palaeorecords provide a means to study repeated pulse disturbances and processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, sedimentary DNA was extracted from a sediment core from Lake Paringa (New Zealand) that is situated in a near natural catchment. Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1100 years - a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, ~50 years) phases directly after the earthquakes and more stable (interseismic, ~250 years) phases, indicating a lack of community resistance. Although community structure differed significantly in successive postseismic phases, function did not, suggesting potential functional redundancy. Significant differences in composition and function in successive interseismic phases demonstrate that communities are not resilient to large-scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa (responsible for driving differences in communities between phases) in the fourth interseismic phase probably represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes.
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http://dx.doi.org/10.1111/mec.16110DOI Listing
October 2021

Variability in microcystin quotas during a Microcystis bloom in a eutrophic lake.

PLoS One 2021 21;16(7):e0254967. Epub 2021 Jul 21.

Australian Rivers Institute, Griffith University, Brisbane, Australia.

Microcystis is a bloom-forming genus of cyanobacteria with some genotypes that produce highly toxic microcystin hepatotoxins. In waterbodies where biological and physical factors are relatively homogenous, toxin quotas (the average amount of toxin per cell), at a single point in time, are expected to be relatively constant. In this study we challenged this assumption by investigating the spatial distribution of microcystin quotas at a single point in time on two separate occasions in a lake with a major Microcystis bloom. Microcystis cell concentrations varied widely across the lake on both sampling occasions (730- and 137-fold) together with microcystin quotas (148- and 362-fold). Cell concentrations and microcystin quotas were strongly positively correlated (R2 = 0.89, P < 0.001, n = 28; R2 = 0.67, P < 0.001, n = 25). Analysis of Microcystis strains using high-throughput sequencing of the 16S-23S rRNA intergenic spacer region showed no relationship between microcystin quota and the relative abundance of specific sequences. Collectively, the results of this study indicate an association between microcystin production and cell density that magnifies the potential for bloom toxicity at elevated cell concentrations.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0254967PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294494PMC
November 2021

Phospholipid fatty acid (PLFA) analysis as a tool to estimate absolute abundances from compositional 16S rRNA bacterial metabarcoding data.

J Microbiol Methods 2021 09 17;188:106271. Epub 2021 Jun 17.

School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand; Centre for Biodiversity and Restoration Ecology, Victoria University of Wellington, Wellington 6012, New Zealand. Electronic address:

Microbial biodiversity monitoring through the analysis of DNA extracted from environmental samples is increasingly popular because it is perceived as being rapid, cost-effective, and flexible concerning the sample types studied. DNA can be extracted from diverse media before high-throughput sequencing of the prokaryotic 16S rRNA gene is used to characterize the taxonomic diversity and composition of the sample (known as metabarcoding). While sources of bias in metabarcoding methodologies are widely acknowledged, previous studies have focused mainly on the effects of these biases within a single substrate type, and relatively little is known of how these vary across substrates. We investigated the effect of substrate type (water, microbial mats, lake sediments, stream sediments, soil and a mock microbial community) on the relative performance of DNA metabarcoding in parallel with phospholipid fatty acid (PLFA) analysis. Quantitative estimates of the biomass of different taxonomic groups in samples were made through the analysis of PLFAs, and these were compared to the relative abundances of microbial taxa estimated from metabarcoding. Furthermore, we used the PLFA-based quantitative estimates of the biomass to adjust relative abundances of microbial groups determined by metabarcoding to provide insight into how the biomass of microbial taxa from PLFA analysis can improve understanding of microbial communities from environmental DNA samples. We used two sets of PLFA biomarkers that differed in their number of PLFAs to evaluate how PLFA biomarker selection influences biomass estimates. Metabarcoding and PLFA analysis provided significantly different views of bacterial composition, and these differences varied among substrates. We observed the most notable differences for the Gram-negative bacteria, which were overrepresented by metabarcoding in comparison to PLFA analysis. In contrast, the relative biomass and relative sequence abundances aligned reasonably well for Cyanobacteria across the tested freshwater substrates. Adjusting relative abundances of microbial taxa estimated by metabarcoding with PLFA-based quantification estimates of the microbial biomass led to significant changes in the microbial community compositions in all substrates. We recommend including independent estimates of the biomass of microbial groups to increase comparability among metabarcoding libraries from environmental samples, especially when comparing communities associated with different substrates.
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http://dx.doi.org/10.1016/j.mimet.2021.106271DOI Listing
September 2021

Spatial abundance and distribution of picocyanobacterial communities in two contrasting lakes revealed using environmental DNA metabarcoding.

FEMS Microbiol Ecol 2021 06;97(7)

Cawthron Institute, 98 Halifax St East, Private Bag 2, Nelson 7042, New Zealand.

Freshwater picocyanobacteria (Pcy) are important yet understudied components of lake ecosystems. Most previous studies have relied on cell abundances to assess Pcy dynamics in largely oligotrophic lakes, while little is known about spatial diversity and dynamics across different lake types. In the present study we assessed the horizontal-spatial abundance and community structure of Pcy in two contrasting (oligotrophic and hypertrophic) New Zealand lakes using epifluorescence microscopy and 16S rRNA metabarcoding. Pcy abundance and community composition differed significantly both between and within the oligotrophic and hypertrophic lakes. While spatial variability was observed in both study lakes, these differences were particularly pronounced in the oligotrophic, morphometrically complex Lake Wanaka where cell abundances were typically higher in bays than open-water sites and community structure differed significantly between sites. Community structuring appeared to be driven by localised environmental conditions, with different factors influencing each lake. These results suggest that single spot-samples are insufficient to gain an understanding of Pcy dynamics and consequently, phytoplankton dynamics in lakes.
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http://dx.doi.org/10.1093/femsec/fiab075DOI Listing
June 2021

Spatial abundance and distribution of picocyanobacterial communities in two contrasting lakes revealed using environmental DNA metabarcoding.

FEMS Microbiol Ecol 2021 06;97(7)

Cawthron Institute, 98 Halifax St East, Private Bag 2, Nelson 7042, New Zealand.

Freshwater picocyanobacteria (Pcy) are important yet understudied components of lake ecosystems. Most previous studies have relied on cell abundances to assess Pcy dynamics in largely oligotrophic lakes, while little is known about spatial diversity and dynamics across different lake types. In the present study we assessed the horizontal-spatial abundance and community structure of Pcy in two contrasting (oligotrophic and hypertrophic) New Zealand lakes using epifluorescence microscopy and 16S rRNA metabarcoding. Pcy abundance and community composition differed significantly both between and within the oligotrophic and hypertrophic lakes. While spatial variability was observed in both study lakes, these differences were particularly pronounced in the oligotrophic, morphometrically complex Lake Wanaka where cell abundances were typically higher in bays than open-water sites and community structure differed significantly between sites. Community structuring appeared to be driven by localised environmental conditions, with different factors influencing each lake. These results suggest that single spot-samples are insufficient to gain an understanding of Pcy dynamics and consequently, phytoplankton dynamics in lakes.
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http://dx.doi.org/10.1093/femsec/fiab075DOI Listing
June 2021

Beyond taxonomy: Validating functional inference approaches in the context of fish-farm impact assessments.

Mol Ecol Resour 2021 Oct 28;21(7):2264-2277. Epub 2021 May 28.

Institute of Marine Research, Tromsø, Norway.

Characterization of microbial assemblages via environmental DNA metabarcoding is increasingly being used in routine monitoring programs due to its sensitivity and cost-effectiveness. Several programs have recently been developed which infer functional profiles from 16S rRNA gene data using hidden-state prediction (HSP) algorithms. These might offer an economic and scalable alternative to shotgun metagenomics. To date, HSP-based methods have seen limited use for benthic marine surveys and their performance in these environments remains unevaluated. In this study, 16S rRNA metabarcoding was applied to sediment samples collected at 0 and ≥1,200 m from Norwegian salmon farms, and three metabolic inference approaches (Paprica, Picrust2 and Tax4Fun2) evaluated against metagenomics and environmental data. While metabarcoding and metagenomics recovered a comparable functional diversity, the taxonomic composition differed between approaches, with genera richness up to 20× higher for metabarcoding. Comparisons between the sensitivity (highest true positive rates) and specificity (lowest true negative rates) of HSP-based programs in detecting functions found in metagenomic data ranged from 0.52 and 0.60 to 0.76 and 0.79, respectively. However, little correlation was observed between the relative abundance of their specific functions. Functional beta-diversity of HSP-based data was strongly associated with that of metagenomics (r ≥ 0.86 for Paprica and Tax4Fun2) and responded similarly to the impact of fish farm activities. Our results demonstrate that although HSP-based metabarcoding approaches provide a slightly different functional profile than metagenomics, partly due to recovering a distinct community, they represent a cost-effective and valuable tool for characterizing and assessing the effects of fish farming on benthic ecosystems.
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http://dx.doi.org/10.1111/1755-0998.13426DOI Listing
October 2021

Investigating variability in microbial community composition in replicate environmental DNA samples down lake sediment cores.

PLoS One 2021 3;16(5):e0250783. Epub 2021 May 3.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Lake sediments are natural archives that accumulate information on biological communities and their surrounding catchments. Paleolimnology has traditionally focussed on identifying fossilized organisms to reconstruct past environments. In the last decade, the application of molecular methodologies has increased in paleolimnological studies, but further research investigating factors such as sample heterogeneity and DNA degradation are required. In the present study we investigated bacterial community heterogeneity (16S rRNA metabarcoding) within depth slices (1-cm width). Sediment cores were collected from three lakes with differing sediment compositions. Samples were collected from a variety of depths which represent a period of time of approximately 1,200 years. Triplicate samples were collected from each depth slice and bacterial 16S rRNA metabarcoding was undertaken on each sample. Accumulation curves demonstrated that except for the deepest (oldest) slices, the combination of three replicate samples were insufficient to characterise the entire bacterial diversity. However, shared Amplicon Sequence Variants (ASVs) accounted for the majority of the reads in each depth slice (max. shared proportional read abundance 96%, 86%, 65% in the three lakes). Replicates within a depth slice generally clustered together in the Non-metric multidimensional scaling analysis. There was high community dissimilarity in older sediment in one of the cores, which was likely due to the laminae in the sediment core not being horizontal. Given that most paleolimnology studies explore broad scale shifts in community structure rather than seeking to identify rare species, this study demonstrates that a single sample is adequate to characterise shifts in dominant bacterial ASVs.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0250783PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8092796PMC
October 2021

A Microencapsulation Method for Delivering Tetrodotoxin to Bivalves to Investigate Uptake and Accumulation.

Mar Drugs 2021 Jan 13;19(1). Epub 2021 Jan 13.

Department of Biological Sciences, University of Waikato, Hamilton 3216, New Zealand.

Most marine biotoxins are produced by microalgae. The neurotoxin tetrodotoxin (TTX) has been reported in many seafood species worldwide but its source is unknown, making accumulation and depuration studies in shellfish difficult. Tetrodotoxin is a water-soluble toxin and cannot be directly ingested by shellfish. In the present study, a method was developed which involved binding TTX to solid particles of humic acid and encapsulating them in agar-gelatin capsules. A controlled quantity of TTX-containing microcapsules (size range 20-280 μm) was fed to , a bivalve known to accumulate TTX in the wild. The TTX-containing microcapsules were fed to every second day for 13 days. Ten (including five controls fed non-toxic microalgae) were harvested after 7 days and ten after 13 days. accumulated TTX, reaching concentrations of up to 103 µg kg by day 13, exceeding the European Food Safety Authority recommended concentration of 44 μg kg in shellfish. This novel method will allow future studies to explore the effects, accumulation and depuration rates of TTX in different animals and document how it is transferred through food webs.
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http://dx.doi.org/10.3390/md19010033DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828407PMC
January 2021

Biosecurity implications of drifting marine plastic debris: Current knowledge and future research.

Mar Pollut Bull 2021 Jan 19;162:111835. Epub 2020 Nov 19.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand; Institute of Marine Science, University of Auckland, Auckland, New Zealand.

The introduction and spread of marine non-indigenous species (NIS) and pathogens into new habitats are a major threat to biodiversity, ecosystem services, human health, and can have substantial economic consequences. Shipping is considered the main vector for marine biological invasions; less well understood is the increased spread of marine NIS and pathogens rafting on marine plastic debris (MPD). Despite an increasing research interest and recent progress in characterizing the plastisphere, this manuscript highlights critical knowledge gaps and research priorities towards a better understanding of the biosecurity implications of MPD. We advocate for future research to (i) investigate plastisphere community succession and the factors influencing NIS propagules and pathogens recruitment through robust experimental investigations; (ii) combine microscopy and molecular approaches to effectively assess the presence of specific taxa; (iii) include additional genetic markers to thoroughly characterize the biodiversity associated with MPD and explore the presence of specific marine pests.
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http://dx.doi.org/10.1016/j.marpolbul.2020.111835DOI Listing
January 2021

Comparing sediment DNA extraction methods for assessing organic enrichment associated with marine aquaculture.

PeerJ 2020 27;8:e10231. Epub 2020 Oct 27.

Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand.

Marine sediments contain a high diversity of micro- and macro-organisms which are important in the functioning of biogeochemical cycles. Traditionally, anthropogenic perturbation has been investigated by identifying macro-organism responses along gradients. Environmental DNA (eDNA) analyses have recently been advocated as a rapid and cost-effective approach to measuring ecological impacts and efforts are underway to incorporate eDNA tools into monitoring. Before these methods can replace or complement existing methods, robustness and repeatability of each analytical step has to be demonstrated. One area that requires further investigation is the selection of sediment DNA extraction method. Environmental DNA sediment samples were obtained along a disturbance gradient adjacent to a Chinook () salmon farm in Otanerau Bay, New Zealand. DNA was extracted using four extraction kits (Qiagen DNeasy PowerSoil, Qiagen DNeasy PowerSoil Pro, Qiagen RNeasy PowerSoil Total RNA/DNA extraction/elution and Favorgen FavorPrep Soil DNA Isolation Midi Kit) and three sediment volumes (0.25, 2, and 5 g). Prokaryotic and eukaryotic communities were amplified using primers targeting the 16S and 18S ribosomal RNA genes, respectively, and were sequenced on an Illumina MiSeq. Diversity and community composition estimates were obtained from each extraction kit, as well as their relative performance in established metabarcoding biotic indices. Differences were observed in the quality and quantity of the extracted DNA amongst kits with the two Qiagen DNeasy PowerSoil kits performing best. Significant differences were observed in both prokaryotes and eukaryotes ( < 0.001) richness among kits. A small proportion of amplicon sequence variants (ASVs) were shared amongst the kits (~3%) although these shared ASVs accounted for the majority of sequence reads (prokaryotes: 59.9%, eukaryotes: 67.2%). Differences were observed in the richness and relative abundance of taxonomic classes revealed with each kit. Multivariate analysis showed that there was a significant interaction between "distance" from the farm and "kit" in explaining the composition of the communities, with the distance from the farm being a stronger determinant of community composition. Comparison of the kits against the bacterial and eukaryotic metabarcoding biotic index suggested that all kits showed similar patterns along the environmental gradient. Overall, we advocate for the use of Qiagen DNeasy PowerSoil kits for use when characterizing prokaryotic and eukaryotic eDNA from marine farm sediments. We base this conclusion on the higher DNA quality values and richness achieved with these kits compared to the other kits/amounts investigated in this study. The additional advantage of the PowerSoil Kits is that DNA extractions can be performed using an extractor robot, offering additional standardization and reproducibility of results.
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http://dx.doi.org/10.7717/peerj.10231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7597629PMC
October 2020

Is a Central Sediment Sample Sufficient? Exploring Spatial and Temporal Microbial Diversity in a Small Lake.

Toxins (Basel) 2020 09 9;12(9). Epub 2020 Sep 9.

Human and Environmental Toxicology, Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.

(1) Background: Paleolimnological studies use sediment cores to explore long-term changes in lake ecology, including occurrences of harmful cyanobacterial blooms. Most studies are based on single cores, assuming this is representative of the whole lake, but data on small-scale spatial variability of microbial communities in lake sediment are scarce. (2) Methods: Surface sediments (top 0.5 cm) from 12 sites ( = 36) and two sediment cores were collected in Lake Rotorua (New Zealand). Bacterial community (16S rRNA metabarcoding), specific 16S rRNA, microcystin synthetase gene E () and microcystins (MCs) were assessed. Radionuclide measurements (Pb, Cs) were used to date sediments. (3) Results: Bacterial community, based on relative abundances, differed significantly between surface sediment sites ( < 0.001) but the majority of bacterial amplicon sequence variants (88.8%) were shared. Despite intense MC producing blooms in the past, no specific 16S rRNA, and MCs were found in surface sediments but occurred deeper in sediment cores (approximately 1950's). Pb measurements showed a disturbed profile, similar to patterns previously observed, as a result of earthquakes. (4) Conclusions: A single sediment core can capture dominant microbial communities. Toxin producing blooms are a recent phenomenon in Lake Rotorua. We posit that the absence of from the surface sediments is a consequence of the Kaikoura earthquake two years prior to our sampling.
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http://dx.doi.org/10.3390/toxins12090580DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7551157PMC
September 2020

Seasonal and Spatial Variations in Bacterial Communities From Tetrodotoxin-Bearing and Non-tetrodotoxin-Bearing Clams.

Front Microbiol 2020 5;11:1860. Epub 2020 Aug 5.

Coastal and Freshwater, Cawthron Institute, Nelson, New Zealand.

Tetrodotoxin (TTX) is one of the most potent naturally occurring compounds and is responsible for many human intoxications worldwide. are endemic clams to New Zealand which contain varying concentrations of TTX. Research suggests that accumulate the toxin exogenously, but the source remains uncertain. The aim of this study was to identify potential bacterial TTX-producers by exploring differences in bacterial communities in two organs of : the siphon and digestive gland. Samples from the digestive glands of a non-toxic bivalve that lives amongst toxic populations were also analyzed. Bacterial communities were characterized using 16S ribosomal RNA gene metabarcoding in sourced monthly from the Hokianga Harbor, a site known to have TTX-bearing clams, for 1 year, from ten sites with varying TTX concentrations around New Zealand, and in from the Hokianga Harbor. Tetrodotoxin was detected in from sites all around New Zealand and in all collected monthly from the Hokianga Harbor. The toxin averaged 150 μg kg over the year of sampling in the Hokianga Harbor but no TTX was detected in the samples from the same site. Bacterial species diversity differed amongst sites ( < 0.001, = 5.9) and the diversity in siphon samples was significantly higher than in digestive glands ( < 0.001, = 65.8). Spirochaetaceae (4-60%) and Mycoplasmataceae (16-78%) were the most abundant families in the siphons and the digestive glands, respectively. The bacterial communities were compared between sites with the lowest TTX concentrations and the Hokianga Harbor (site with the highest TTX concentrations), and the core bacterial communities from TTX-bearing individuals were analyzed. The results from both spatial and temporal studies corroborate with previous hypotheses that and could be responsible for the source of TTX in bivalves. The results from this study also indicate that marine cyanobacteria, in particular picocyanobacteria (e.g., , , , and s), should be investigated further as potential TTX producers.
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http://dx.doi.org/10.3389/fmicb.2020.01860DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7419435PMC
August 2020

Acute toxicity of dihydroanatoxin-a from Microcoleus autumnalis in comparison to anatoxin-a.

Chemosphere 2021 Jan 13;263:127937. Epub 2020 Aug 13.

AgResearch Limited, Ruakura Research Centre, Private Bag 3123, Hamilton, 3240, New Zealand.

The cyanobacterium Microcoleus autumnalis grows as thick benthic mats in rivers and is becoming increasingly prevalent around the world. M. autumnalis can produce high concentrations of anatoxins and ingestion of benthic mats has led to multiple dog deaths over the past two decades. M. autumnalis produces a suite of different anatoxin congeners including anatoxin-a (ATX), dihydroanatoxin-a, (dhATX), homoanatoxin-a and dihydrohomoanatoxin-a. Benthic mat samples often contain high levels of dhATX, but there is little toxicology information on this congener. In the present study, natural versions of dhATX and ATX were purified from cyanobacteria to determine the acute toxicity by different routes of administration using mice. Nuclear magnetic resonance spectroscopy was used to confirm the putative structure of dhATX. By intraperitoneal (ip) injection, the median lethal dose (LD) for dhATX was 0.73 mg/kg, indicating a reduced toxicity compared to ATX (LD of 0.23 mg/kg). However, by oral administration (both gavage and feeding), dhATX was more toxic than ATX (gavage LD of 2.5 mg/kg for dhATX and 10.6 mg/kg for ATX; feeding LD of 8 mg/kg for dhATX and 25 mg/kg for ATX). The relative nicotinic acetylcholine receptor-binding affinities of ATX and dhATX were determined using the Torpedo electroplaque assay which showed consistency with the relative toxicity determined by ip injection. This work highlights that toxicity studies based solely on ip injection may not yield LD values that are relevant to those derived via oral administration, and hence, do not provide a good estimate of the risk posed to human and animal health in situations where oral ingestion is the likely route of exposure. The high acute oral toxicity of dhATX, and its abundance in M. autumnalis proliferations, demonstrates that it is an important environmental contaminant that warrants further investigation.
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http://dx.doi.org/10.1016/j.chemosphere.2020.127937DOI Listing
January 2021

Predicting cyanobacterial biovolumes from phycocyanin fluorescence using a handheld fluorometer in the field.

Harmful Algae 2020 07 9;97:101869. Epub 2020 Jul 9.

Cawthron Institute, Private Bag 2, Nelson 7010, New Zealand.

Toxic cyanobacterial blooms are becoming more prevalent in freshwater systems, increasing the need for monitoring to protect human health. Phycocyanin fluorescence sensors have been developed as tools for providing fast and cost-effective proxy measurements for cyanobacterial biomass. However, poor precision and low sensitivity in many of the probe sensors assessed to-date has restricted their potential for practical application in cyanobacterial monitoring programmes. In the present study, the sensitivity and accuracy of a handheld fluorometer, the CyanoFluor, was assessed using 12 cyanobacterial strains and samples from four different lakes collected weekly for 12 weeks. After the initial measurements, the samples were lysed by sonication, which we hypothesised would reduce inter and intra-specific differences. The CyanoFluor displayed high sensitivity (limit of quantification = 3.5 µg L of phycocyanin) and was able to detect cyanobacterial biovolumes to levels much lower than the threshold levels in current recreational guidelines worldwide. There were strong and significant phycocyanin to biovolume relationships (r ≥ 0.88, P < 0.05) for all 12 cyanobacterial cultures. Collectively, strong relationships between phycocyanin fluorescence and cyanobacterial biovolumes were also identified in environmental samples (r ≥ 0.78, P < 0.001), although weaker relationships were identified when lakes were analysed separately (r = 0.06 - 0.90). There were differences in phycocyanin per biovolume between both cultured strains and lakes, highlighting innate interspecific differences that exist between cyanobacterial species. Lysis of samples consistently reduced variability between technical replicates, in cyanobacteria cultures (up to 87% reduction in sample variability) and environmental samples (71 - 93% reduction), indicating that it would be a useful methodological step to improve the repeatability of results. When guideline thresholds (aligned with currently enforced risk assessment categories) were modelled based on the most successful linear regression model, 74% of samples were assigned to the correct risk category. The sensitivity of the CyanoFluor and accuracy of the phycocyanin threshold models, indicates high potential for this method to be integrated into cyanobacterial monitoring programmes.
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http://dx.doi.org/10.1016/j.hal.2020.101869DOI Listing
July 2020

Elucidating Biodiversity Shifts in Ballast Water Tanks during a Cross-Latitudinal Transfer: Complementary Insights from Molecular Analyses.

Environ Sci Technol 2020 07 9;54(13):8443-8454. Epub 2020 Jun 9.

Department of Functional Biology, University of Oviedo, C/Julian Claveria s/n, 33006 Oviedo, Spain.

In this study, the evolution of ballast water (BW) assemblages across different trophic levels was characterized over a 21 day cross-latitudinal vessel transit using a combination of molecular methods. Triplicate BW samples were collected every second day and size-fractionated (<2.7, 10, >50 μm). Measurements of adenosine triphosphate (ATP) and metabarcoding of environmental nucleic acid (DNA and RNA) analyses, complemented by microscopy and flow cytometry, were performed on each sample. Measured ATP concentrations exhibited high variance between replicates and a strong negative trend in the large (≥50 μm) fraction over the voyage. In concert with microscopy, the metabarcoding data indicated a die-off of larger metazoans during the first week of study and gradual reductions in dinoflagellates and ochrophytes. The ATP and metabarcoding data signaled persistent or increased cellular activity of heterotrophic bacteria and protists in the BW, which was supported by flow cytometry. The metabarcoding showed the presence of active bacteria in all size fractions, suggesting that the sequential filtration approach does not ensure taxonomical differentiation, which has implications for BW quality assessment. Although our data show that ATP and metabarcoding have potential for indicative BW screening for BW compliance monitoring, further research and technological development is needed to improve representativeness of sampling and deliver the unequivocal response criteria required by the international Ballast Water Management Convention.
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http://dx.doi.org/10.1021/acs.est.0c01931DOI Listing
July 2020

Local factors drive bacterial and microeukaryotic community composition in lake surface sediment collected across an altitudinal gradient.

FEMS Microbiol Ecol 2020 06;96(6)

Cawthron Institute, Coastal and Freshwater Group, 95 Halifax Street East, Nelson, 7010, New Zealand.

Lake surface sediments are dominated by microorganisms that play significant roles in biogeochemical cycling within lakes. There is limited knowledge on the relative importance of local environmental factors and altitude on bacterial and microeukaryotic community richness and composition in lake sediments. In the present study, surface sediment samples were collected from 40 lakes along an altitude gradient (2-1215 m). Microbial communities were characterized using 16S (bacteria) and 18S (microeukaryotes) rRNA gene metabarcoding. Bacterial and microeukaryotic richness were not correlated with altitude but instead to environmental variables (e.g. area of water in the catchment (bacteria: R = -0.43). For both bacteria and microeukaryotes, dissimilarity in the community structure had a higher correlation to combined environmental variables (without altitude) (bacteria: R = 0.53; microeukaryotes: R = 0.55) than altitude alone (bacteria: R = 0.34; microeukaryotes: R = 0.47). Sediment sulfur and productive grassland were important variables in determining the relative abundance of sulfate reducing bacteria. Nitrospira, was positively related to altitude but negatively to water column total organic carbon and the proportion of productive grassland in the catchment. Little overlap in amplicon sequence variants was shown amongst lakes. This has important considerations for management decisions, suggesting that to protect biodiversity, conservation of numerous lakes and lake types is required.
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http://dx.doi.org/10.1093/femsec/fiaa070DOI Listing
June 2020

Limited Microcystin, Anatoxin and Cylindrospermopsin Production by Cyanobacteria from Microbial Mats in Cold Deserts.

Toxins (Basel) 2020 04 11;12(4). Epub 2020 Apr 11.

Institute of Environmental Biology, Faculty of Biology, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089 Warsaw, Poland.

Toxic metabolites are produced by many cyanobacterial species. There are limited data on toxigenic benthic, mat-forming cyanobacteria, and information on toxic cyanobacteria from Central Asia is even more scarce. In the present study, we examined cyanobacterial diversity and community structure, the presence of genes involved in toxin production and the occurrence of cyanotoxins in cyanobacterial mats from small water bodies in a cold high-mountain desert of Eastern Pamir. Diversity was explored using amplicon-based sequencing targeting the V3-V4 region of the 16S rRNA gene, toxin potential using PCR-based methods (), and toxins by enzyme-linked immunosorbent assays (ELISAs) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Molecular identification of cyanobacteria showed a high similarity of abundant taxa to PCC-73102, PCC-7524, PCC935 and CYN68. The PCRs revealed the presence of and/or genes in 11 samples and in six. The partial sequences of the gene showed high sequence similarity to , and uncultured cyanobacteria. LC-MS/MS analysis identified six microcystin congeners in two samples and unknown peptides in one. These results suggest that, in this extreme environment, cyanobacteria do not commonly produce microcystins, anatoxins and cylindrospermopsins, despite the high diversity and widespread occurrence of potentially toxic taxa.
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http://dx.doi.org/10.3390/toxins12040244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7232524PMC
April 2020

Broad and Fine Scale Variability in Bacterial Diversity and Cyanotoxin Quotas in Benthic Cyanobacterial Mats.

Front Microbiol 2020 6;11:129. Epub 2020 Feb 6.

Cawthron Institute, Nelson, New Zealand.

Benthic proliferations of (basionym ) and closely related taxa are being reported with increasing frequency in streams and rivers worldwide. This species commonly produces the potent neurotoxin anatoxin, and exposure to this has resulted in animal fatalities and human health concerns. Bacterial communities within cyanobacterial assemblages can facilitate processes such as nutrient cycling and are posited to influence cyanobacterial growth and function. However, there is limited knowledge on spatial variability of bacterial communities associated with benthic cyanobacteria and anatoxin content and quotas. In this study, -dominated mat samples were collected from six sites in two New Zealand streams. Associated bacterial communities were characterized using 16S rRNA metabarcoding, anatoxin content by liquid chromatography-mass spectrometry and copies using droplet digital PCR. Bacterial assemblages differed significantly when amplicon sequence variants were compared between streams and most sites within streams. These differences were associated with conductivity, DRP, DIN, temperature, anatoxin concentration, and quota. Despite the differences in bacterial community composition; at phyla, class and order levels there was high similarity across spatial scales, with Bacteroidetes (ca. 67%) and Proteobacteria (ca. 25%) dominant. There was significant variability in total anatoxin concentrations between sites in both streams ( < 0.001). When the data were converted to anatoxin quotas variability was reduced, suggesting that the relative abundance of toxic genotypes is a key driver of total anatoxin concentrations in mats. This study demonstrates the complexity of microbial communities within -dominated mats and highlights their likely important role in within-mat nutrient cycling processes.
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http://dx.doi.org/10.3389/fmicb.2020.00129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7017413PMC
February 2020

Multiple cyanotoxin congeners produced by sub-dominant cyanobacterial taxa in riverine cyanobacterial and algal mats.

PLoS One 2019 16;14(12):e0220422. Epub 2019 Dec 16.

Cawthron Institute, The Wood, Nelson, New Zealand.

Benthic cyanobacterial proliferations in rivers are have been reported with increasing frequency worldwide. In the Eel and Russian rivers of California, more than a dozen dog deaths have been attributed to cyanotoxin toxicosis since 2000. Periphyton proliferations in these rivers comprise multiple cyanobacterial taxa capable of cyanotoxin production, hence there is uncertainty regarding which taxa are producing toxins. In this study, periphyton samples dominated by the cyanobacterial genera Anabaena spp. and Microcoleus spp. and the green alga Cladophora glomerata were collected from four sites in the Eel River catchment and one site in the Russian River. Samples were analysed for potential cyanotoxin producers using polymerase chain reaction (PCR) in concert with Sanger sequencing. Cyanotoxin concentrations were measured using liquid chromatography tandem-mass spectrometry, and anatoxin quota (the amount of cyanobacterial anatoxins per toxigenic cell) determined using droplet digital PCR. Sequencing indicated Microcoleus sp. and Nodularia sp. were the putative producers of cyanobacterial anatoxins and nodularins, respectively, regardless of the dominant taxa in the mat. Anatoxin concentrations in the mat samples varied from 0.1 to 18.6 μg g-1 and were significantly different among sites (p < 0.01, Wilcoxon test); however, anatoxin quotas were less variable (< 5-fold). Dihydroanatoxin-a was generally the most abundant variant in samples comprising 38% to 71% of the total anatoxins measured. Mats dominated by the green alga C. glomerata contained both anatoxins and nodularin-R at concentrations similar to those of cyanobacteria-dominated mats. This highlights that even when cyanobacteria are not the dominant taxa in periphyton, these mats may still pose a serious health risk and indicates that more widespread monitoring of all mats in a river are necessary.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0220422PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6913960PMC
March 2020
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