Publications by authors named "Margarete Watzka"

16 Publications

  • Page 1 of 1

Genomic insights into diverse bacterial taxa that degrade extracellular DNA in marine sediments.

Nat Microbiol 2021 07 14;6(7):885-898. Epub 2021 Jun 14.

Division of Microbial Ecology, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Extracellular DNA is a major macromolecule in global element cycles, and is a particularly crucial phosphorus, nitrogen and carbon source for microorganisms in the seafloor. Nevertheless, the identities, ecophysiology and genetic features of DNA-foraging microorganisms in marine sediments are largely unknown. Here, we combined microcosm experiments, DNA stable isotope probing (SIP), single-cell SIP using nano-scale secondary isotope mass spectrometry (NanoSIMS) and genome-centric metagenomics to study microbial catabolism of DNA and its subcomponents in marine sediments. C-DNA added to sediment microcosms was largely degraded within 10 d and mineralized to CO. SIP probing of DNA revealed diverse 'Candidatus Izemoplasma', Lutibacter, Shewanella and Fusibacteraceae incorporated DNA-derived C-carbon. NanoSIMS confirmed incorporation of C into individual bacterial cells of Fusibacteraceae sorted from microcosms. Genomes of the C-labelled taxa all encoded enzymatic repertoires for catabolism of DNA or subcomponents of DNA. Comparative genomics indicated that diverse 'Candidatus Izemoplasmatales' (former Tenericutes) are exceptional because they encode multiple (up to five) predicted extracellular nucleases and are probably specialized DNA-degraders. Analyses of additional sediment metagenomes revealed extracellular nuclease genes are prevalent among Bacteroidota at diverse sites. Together, our results reveal the identities and functional properties of microorganisms that may contribute to the key ecosystem function of degrading and recycling DNA in the seabed.
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http://dx.doi.org/10.1038/s41564-021-00917-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8289736PMC
July 2021

Nitrogen Isotope Fractionation During Archaeal Ammonia Oxidation: Coupled Estimates From Measurements of Residual Ammonium and Accumulated Nitrite.

Front Microbiol 2020 28;11:1710. Epub 2020 Jul 28.

Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

The naturally occurring nitrogen (N) isotopes, N and N, exhibit different reaction rates during many microbial N transformation processes, which results in N isotope fractionation. Such isotope effects are critical parameters for interpreting natural stable isotope abundances as proxies for biological process rates in the environment across scales. The kinetic isotope effect of ammonia oxidation (AO) to nitrite (NO ), performed by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), is generally ascribed to the enzyme ammonia monooxygenase (AMO), which catalyzes the first step in this process. However, the kinetic isotope effect of AMO, or ε , has been typically determined based on isotope kinetics during product formation (cumulative product, NO ) alone, which may have overestimated ε due to possible accumulation of chemical intermediates and alternative sinks of ammonia/ammonium (NH/NH ). Here, we analyzed N isotope fractionation during archaeal ammonia oxidation based on both isotopic changes in residual substrate (RS, NH ) and cumulative product (CP, NO ) pools in pure cultures of the soil strain EN76 and in highly enriched cultures of the marine strain NF5, under non-limiting substrate conditions. We obtained ε values of 31.9-33.1‰ for both strains based on RS (δNH ) and showed that estimates based on CP (δNO ) give larger isotope fractionation factors by 6-8‰. Complementary analyses showed that, at the end of the growth period, microbial biomass was N-enriched (10.1‰), whereas nitrous oxide (NO) was highly N depleted (-38.1‰) relative to the initial substrate. Although we did not determine the isotope effect of NH assimilation (biomass formation) and NO production by AOA, our results nevertheless show that the discrepancy between ε estimates based on RS and CP might have derived from the incorporation of N-enriched residual NH after AMO reaction into microbial biomass and that NO production did not affect isotope fractionation estimates significantly.
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http://dx.doi.org/10.3389/fmicb.2020.01710DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7399158PMC
July 2020

Quantifying microbial growth and carbon use efficiency in dry soil environments via O water vapor equilibration.

Glob Chang Biol 2020 Sep 24;26(9):5333-5341. Epub 2020 Jun 24.

Terrestrial Ecosystem Research, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Soil microbial physiology controls large fluxes of C to the atmosphere, thus, improving our ability to accurately quantify microbial physiology in soil is essential. However, current methods to determine microbial C metabolism require liquid water addition, which makes it practically impossible to measure microbial physiology in dry soil samples without stimulating microbial growth and respiration (namely, the "Birch effect"). We developed a new method based on in vivo O-water vapor equilibration to minimize soil rewetting effects. This method allows the isotopic labeling of soil water without direct liquid water addition. This was compared to the main current method (direct O-liquid water addition) in moist and air-dry soils. We determined the time kinetics and calculated the average O enrichment of soil water over incubation time, which is necessary to calculate microbial growth from O incorporation in genomic DNA. We tested isotopic equilibration patterns in three natural and six artificially constructed soils covering a wide range of soil texture and soil organic matter content. We then measured microbial growth, respiration and carbon use efficiency (CUE) in three natural soils (either air-dry or moist). The proposed O-vapor equilibration method provided similar results as the current method of liquid O-water addition when used for moist soils. However, when applied to air-dry soils the liquid O-water addition method overestimated growth by up to 250%, respiration by up to 500%, and underestimated CUE by up to 40%. We finally describe the new insights into biogeochemical cycling of C that the new method can help uncover, and we consider a range of questions regarding microbial physiology and its response to global change that can now be addressed.
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http://dx.doi.org/10.1111/gcb.15168DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497233PMC
September 2020

Characterization of a thaumarchaeal symbiont that drives incomplete nitrification in the tropical sponge Ianthella basta.

Environ Microbiol 2019 10 25;21(10):3831-3854. Epub 2019 Jul 25.

Centre for Microbiology and Environmental Systems Science, Division of Microbial Ecology, University of Vienna, Austria.

Marine sponges represent one of the few eukaryotic groups that frequently harbour symbiotic members of the Thaumarchaeota, which are important chemoautotrophic ammonia-oxidizers in many environments. However, in most studies, direct demonstration of ammonia-oxidation by these archaea within sponges is lacking, and little is known about sponge-specific adaptations of ammonia-oxidizing archaea (AOA). Here, we characterized the thaumarchaeal symbiont of the marine sponge Ianthella basta using metaproteogenomics, fluorescence in situ hybridization, qPCR and isotope-based functional assays. 'Candidatus Nitrosospongia ianthellae' is only distantly related to cultured AOA. It is an abundant symbiont that is solely responsible for nitrite formation from ammonia in I. basta that surprisingly does not harbour nitrite-oxidizing microbes. Furthermore, this AOA is equipped with an expanded set of extracellular subtilisin-like proteases, a metalloprotease unique among archaea, as well as a putative branched-chain amino acid ABC transporter. This repertoire is strongly indicative of a mixotrophic lifestyle and is (with slight variations) also found in other sponge-associated, but not in free-living AOA. We predict that this feature as well as an expanded and unique set of secreted serpins (protease inhibitors), a unique array of eukaryotic-like proteins, and a DNA-phosporothioation system, represent important adaptations of AOA to life within these ancient filter-feeding animals.
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http://dx.doi.org/10.1111/1462-2920.14732DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6790972PMC
October 2019

Food supply and size class depending variations in phytodetritus intake in the benthic foraminifer .

Biol Open 2018 Apr 13;7(4). Epub 2018 Apr 13.

Department of Palaeontology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.

is a common and abundant benthic foraminifer in intertidal mudflats. Benthic foraminifera are primary consumers and detritivores and act as key players in sediment nutrient fluxes. In this study, laboratory feeding experiments using isotope-labeled phytodetritus were carried out with collected at the German Wadden Sea, to investigate the response of to varying food supply. Feeding mode (single pulse, constant feeding; different incubation temperatures) caused strong variations in cytoplasmic carbon and nitrogen cycling, suggesting generalistic adaptations to variations in food availability. To study the influence of intraspecific size to foraminiferal carbon and nitrogen cycling, three size fractions (125-250 µm, 250-355 µm, >355 µm) of specimens were separated. Small individuals showed higher weight specific intake for phytodetritus, especially for phytodetrital nitrogen, highlighting that size distribution within foraminiferal populations is relevant to interpret foraminiferal carbon and nitrogen cycling. These results were used to extrapolate the data to natural populations of living in sediment cores, demonstrating the impact of high abundances of small individuals on phytodetritus processing and nutrient cycling. It is estimated that at high abundances of individuals in the 125-250 µm size fraction, populations can account for more than 11% of phytodetritus processing in intertidal benthic communities.
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http://dx.doi.org/10.1242/bio.030056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5936058PMC
April 2018

Decoupling of microbial carbon, nitrogen, and phosphorus cycling in response to extreme temperature events.

Sci Adv 2017 May 3;3(5):e1602781. Epub 2017 May 3.

Department of Microbiology and Ecosystem Science, University of Vienna, 1090 Vienna, Austria.

Predicted changes in the intensity and frequency of climate extremes urge a better mechanistic understanding of the stress response of microbially mediated carbon (C) and nutrient cycling processes. We analyzed the resistance and resilience of microbial C, nitrogen (N), and phosphorus (P) cycling processes and microbial community composition in decomposing plant litter to transient, but severe, temperature disturbances, namely, freeze-thaw and heat. Disturbances led temporarily to a more rapid cycling of C and N but caused a down-regulation of P cycling. In contrast to the fast recovery of the initially stimulated C and N processes, we found a slow recovery of P mineralization rates, which was not accompanied by significant changes in community composition. The functional and structural responses to the two distinct temperature disturbances were markedly similar, suggesting that direct negative physical effects and costs associated with the stress response were comparable. Moreover, the stress response of extracellular enzyme activities, but not that of intracellular microbial processes (for example, respiration or N mineralization), was dependent on the nutrient content of the resource through its effect on microbial physiology and community composition. Our laboratory study provides novel insights into the mechanisms of microbial functional stress responses that can serve as a basis for field studies and, in particular, illustrates the need for a closer integration of microbial C-N-P interactions into climate extremes research.
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http://dx.doi.org/10.1126/sciadv.1602781DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5415334PMC
May 2017

Drought history affects grassland plant and microbial carbon turnover during and after a subsequent drought event.

J Ecol 2016 09 24;104(5):1453-1465. Epub 2016 May 24.

Department of Microbiology and Ecosystem Science University of Vienna Althanstrasse 14 A-1090 Vienna Austria.

Drought periods are projected to become more severe and more frequent in many European regions. While effects of single strong droughts on plant and microbial carbon (C) dynamics have been studied in some detail, impacts of recurrent drought events are still little understood.We tested whether the legacy of extreme experimental drought affects responses of plant and microbial C and nitrogen (N) turnover to further drought and rewetting. In a mountain grassland, we conducted a C pulse-chase experiment during a naturally occurring drought and rewetting event in plots previously exposed to experimental droughts and in ambient controls (AC). After labelling, we traced C below-ground allocation and incorporation into soil microbes using phospholipid fatty acid biomarkers.Drought history (DH) had no effects on the standing shoot and fine root plant biomass. However, plants with experimental DH displayed decreased shoot N concentrations and increased fine root N concentrations relative to those in AC. During the natural drought, plants with DH assimilated and allocated less C below-ground; moreover, fine root respiration was reduced and not fuelled by fresh C compared to plants in AC.Regardless of DH, microbial biomass remained stable during natural drought and rewetting. Although microbial communities initially differed in their composition between soils with and without DH, they responded to the natural drought and rewetting in a similar way: gram-positive bacteria increased, while fungal and gram-negative bacteria remained stable. In soils with DH, a strongly reduced uptake of recent plant-derived C in microbial biomarkers was observed during the natural drought, pointing to a smaller fraction of active microbes or to a microbial community that is less dependent on plant C. . Drought history can induce changes in above- vs. below-ground plant N concentrations and affect the response of plant C turnover to further droughts and rewetting by decreasing plant C uptake and below-ground allocation. DH does not affect the responses of the microbial community to further droughts and rewetting, but alters microbial functioning, particularly the turnover of recent plant-derived carbon, during and after further drought periods.
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http://dx.doi.org/10.1111/1365-2745.12593DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4996329PMC
September 2016

Plant-derived compounds stimulate the decomposition of organic matter in arctic permafrost soils.

Sci Rep 2016 05 9;6:25607. Epub 2016 May 9.

Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.

Arctic ecosystems are warming rapidly, which is expected to promote soil organic matter (SOM) decomposition. In addition to the direct warming effect, decomposition can also be indirectly stimulated via increased plant productivity and plant-soil C allocation, and this so called "priming effect" might significantly alter the ecosystem C balance. In this study, we provide first mechanistic insights into the susceptibility of SOM decomposition in arctic permafrost soils to priming. By comparing 119 soils from four locations across the Siberian Arctic that cover all horizons of active layer and upper permafrost, we found that an increased availability of plant-derived organic C particularly stimulated decomposition in subsoil horizons where most of the arctic soil carbon is located. Considering the 1,035 Pg of arctic soil carbon, such an additional stimulation of decomposition beyond the direct temperature effect can accelerate net ecosystem C losses, and amplify the positive feedback to global warming.
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http://dx.doi.org/10.1038/srep25607DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4860603PMC
May 2016

Carbon and Nitrogen Uptake of Calcareous Benthic Foraminifera along a Depth-Related Oxygen Gradient in the OMZ of the Arabian Sea.

Front Microbiol 2016 11;7:71. Epub 2016 Feb 11.

Department of Palaeontology, University of Vienna Vienna, Austria.

Foraminifera are an important faunal element of the benthos in oxygen-depleted settings such as Oxygen Minimum Zones (OMZs) where they can play a relevant role in the processing of phytodetritus. We investigated the uptake of phytodetritus (labeled with (13)C and (15)N) by calcareous foraminifera in the 0-1 cm sediment horizon under different oxygen concentrations within the OMZ in the eastern Arabian Sea. The in situ tracer experiments were carried out along a depth transect on the Indian margin over a period of 4 to 10 days. The uptake of phytodetrital carbon within 4 days by all investigated species shows that phytodetritus is a relevant food source for foraminifera in OMZ sediments. The decrease of total carbon uptake from 540 to 1100 m suggests a higher demand for carbon by species in the low-oxygen core region of the OMZ or less food competition with macrofauna. Especially Uvigerinids showed high uptake of phytodetrital carbon at the lowest oxygenated site. Variation in the ratio of phytodetrital carbon to nitrogen between species and sites indicates that foraminiferal carbon and nitrogen use can be decoupled and different nutritional demands are found between species. Lower ratio of phytodetrital carbon and nitrogen at 540 m could hint for greater demand or storage of food-based nitrogen, ingestion, or hosting of bacteria under almost anoxic conditions. Shifts in the foraminiferal assemblage structure (controlled by oxygen or food availability) and in the presence of other benthic organisms are likely to account for observed changes in the processing of phytodetritus in the different OMZ habitats. Foraminifera dominate the short-term processing of phytodetritus in the OMZ core but are less important in the lower OMZ boundary region of the Indian margin as biological interactions and species distribution of foraminifera change with depth and oxygen levels.
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http://dx.doi.org/10.3389/fmicb.2016.00071DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4749719PMC
February 2016

Capture of algae promotes growth and propagation in aquatic Utricularia.

Ann Bot 2015 Feb 18;115(2):227-36. Epub 2014 Dec 18.

University of Vienna, Core Facility Cell Imaging and Ultrastructure Research, Althanstrasse 14, A-1090 Vienna, Austria, Gregor Mendel Institute for Molecular Plant Biology, Lab Management, Dr. Bohr Gasse 3, A-1030 Vienna, Austria and University of Vienna, Department of Microbiology and Ecosystem Research Silver - Stable Isotope Lab, Althanstrasse 14, A-1090 Vienna, Austria.

Background And Aims: Some carnivorous plants trap not only small animals but also algae and pollen grains. However, it remains unclear if these trapped particles are useless bycatch or whether they provide nutrients for the plant. The present study examines this question in Utricularia, which forms the largest and most widely spread genus of carnivorous plants, and which captures prey by means of sophisticated suction traps.

Methods: Utricularia plants of three different species (U. australis, U. vulgaris and U. minor) were collected in eight different water bodies including peat bogs, lakes and artificial ponds in three regions of Austria. The prey spectrum of each population was analysed qualitatively and quantitatively, and correlated with data on growth and propagation, C/N ratio and δ(15)N.

Key Results: More than 50 % of the prey of the Utricularia populations investigated consisted of algae and pollen, and U. vulgaris in particular was found to capture large amounts of gymnosperm pollen. The capture of algae and pollen grains was strongly correlated with most growth parameters, including weight, length, budding and elongation of internodes. The C/N ratio, however, was less well correlated. Other prey, such as moss leaflets, fungal hyphae and mineral particles, were negatively correlated with most growth parameters. δ(15)N was positively correlated with prey capture, but in situations where algae were the main prey objects it was found that the standard formula for calculation of prey-derived N was no longer applicable.

Conclusions: The mass capture of immotile particles confirms the ecological importance of autonomous firing of the traps. Although the C/N ratio was little influenced by algae, they clearly provide other nutrients, possibly including phosphorus and trace elements. By contrast, mosses, fungi and mineral particles appear to be useless bycatch. Correlations with chemical parameters indicate that Utricularia benefits from nutrient-rich waters by uptake of inorganic nutrients from the water, by the production of more traps per unit of shoot length, and by the capture of more prey particles per trap, as nutrient-rich waters harbour more prey organisms.
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http://dx.doi.org/10.1093/aob/mcu236DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4551088PMC
February 2015

Input of easily available organic C and N stimulates microbial decomposition of soil organic matter in arctic permafrost soil.

Soil Biol Biochem 2014 Aug;75(100):143-151

University of Vienna, Department of Microbiology and Ecosystem Science, Division of Terrestrial Ecosystem Research, Vienna, Austria ; Austrian Polar Research Institute, Vienna, Austria.

Rising temperatures in the Arctic can affect soil organic matter (SOM) decomposition directly and indirectly, by increasing plant primary production and thus the allocation of plant-derived organic compounds into the soil. Such compounds, for example root exudates or decaying fine roots, are easily available for microorganisms, and can alter the decomposition of older SOM ("priming effect"). We here report on a SOM priming experiment in the active layer of a permafrost soil from the central Siberian Arctic, comparing responses of organic topsoil, mineral subsoil, and cryoturbated subsoil material (i.e., poorly decomposed topsoil material subducted into the subsoil by freeze-thaw processes) to additions of C-labeled glucose, cellulose, a mixture of amino acids, and protein (added at levels corresponding to approximately 1% of soil organic carbon). SOM decomposition in the topsoil was barely affected by higher availability of organic compounds, whereas SOM decomposition in both subsoil horizons responded strongly. In the mineral subsoil, SOM decomposition increased by a factor of two to three after any substrate addition (glucose, cellulose, amino acids, protein), suggesting that the microbial decomposer community was limited in energy to break down more complex components of SOM. In the cryoturbated horizon, SOM decomposition increased by a factor of two after addition of amino acids or protein, but was not significantly affected by glucose or cellulose, indicating nitrogen rather than energy limitation. Since the stimulation of SOM decomposition in cryoturbated material was not connected to microbial growth or to a change in microbial community composition, the additional nitrogen was likely invested in the production of extracellular enzymes required for SOM decomposition. Our findings provide a first mechanistic understanding of priming in permafrost soils and suggest that an increase in the availability of organic carbon or nitrogen, e.g., by increased plant productivity, can change the decomposition of SOM stored in deeper layers of permafrost soils, with possible repercussions on the global climate.
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http://dx.doi.org/10.1016/j.soilbio.2014.04.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4064687PMC
August 2014

Adjustment of microbial nitrogen use efficiency to carbon:nitrogen imbalances regulates soil nitrogen cycling.

Nat Commun 2014 Apr 16;5:3694. Epub 2014 Apr 16.

Department of Microbiology and Ecosystem Science, Terrestrial Ecosystem Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.

Microbial nitrogen use efficiency (NUE) describes the partitioning of organic N taken up between growth and the release of inorganic N to the environment (that is, N mineralization), and is thus central to our understanding of N cycling. Here we report empirical evidence that microbial decomposer communities in soil and plant litter regulate their NUE. We find that microbes retain most immobilized organic N (high NUE), when they are N limited, resulting in low N mineralization. However, when the metabolic control of microbial decomposers switches from N to C limitation, they release an increasing fraction of organic N as ammonium (low NUE). We conclude that the regulation of NUE is an essential strategy of microbial communities to cope with resource imbalances, independent of the regulation of microbial carbon use efficiency, with significant effects on terrestrial N cycling.
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http://dx.doi.org/10.1038/ncomms4694DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3997803PMC
April 2014

Metabolic features of Protochlamydia amoebophila elementary bodies--a link between activity and infectivity in Chlamydiae.

PLoS Pathog 2013 8;9(8):e1003553. Epub 2013 Aug 8.

Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria.

The Chlamydiae are a highly successful group of obligate intracellular bacteria, whose members are remarkably diverse, ranging from major pathogens of humans and animals to symbionts of ubiquitous protozoa. While their infective developmental stage, the elementary body (EB), has long been accepted to be completely metabolically inert, it has recently been shown to sustain some activities, including uptake of amino acids and protein biosynthesis. In the current study, we performed an in-depth characterization of the metabolic capabilities of EBs of the amoeba symbiont Protochlamydia amoebophila. A combined metabolomics approach, including fluorescence microscopy-based assays, isotope-ratio mass spectrometry (IRMS), ion cyclotron resonance Fourier transform mass spectrometry (ICR/FT-MS), and ultra-performance liquid chromatography mass spectrometry (UPLC-MS) was conducted, with a particular focus on the central carbon metabolism. In addition, the effect of nutrient deprivation on chlamydial infectivity was analyzed. Our investigations revealed that host-free P. amoebophila EBs maintain respiratory activity and metabolize D-glucose, including substrate uptake as well as host-free synthesis of labeled metabolites and release of labeled CO2 from (13)C-labeled D-glucose. The pentose phosphate pathway was identified as major route of D-glucose catabolism and host-independent activity of the tricarboxylic acid (TCA) cycle was observed. Our data strongly suggest anabolic reactions in P. amoebophila EBs and demonstrate that under the applied conditions D-glucose availability is essential to sustain metabolic activity. Replacement of this substrate by L-glucose, a non-metabolizable sugar, led to a rapid decline in the number of infectious particles. Likewise, infectivity of Chlamydia trachomatis, a major human pathogen, also declined more rapidly in the absence of nutrients. Collectively, these findings demonstrate that D-glucose is utilized by P. amoebophila EBs and provide evidence that metabolic activity in the extracellular stage of chlamydiae is of major biological relevance as it is a critical factor affecting maintenance of infectivity.
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http://dx.doi.org/10.1371/journal.ppat.1003553DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738481PMC
March 2014

An analysis of diet quality, how it controls fatty acid profiles, isotope signatures and stoichiometry in the malaria mosquito Anopheles arabiensis.

PLoS One 2012 25;7(10):e45222. Epub 2012 Oct 25.

Department of Terrestrial Ecosystem Research, University of Vienna, Vienna, Austria.

Background: Knowing the underlying mechanisms of mosquito ecology will ensure effective vector management and contribute to the overall goal of malaria control. Mosquito populations show a high degree of population plasticity in response to environmental variability. However, the principle factors controlling population size and fecundity are for the most part unknown. Larval habitat and diet play a crucial role in subsequent mosquito fitness. Developing the most competitive insects for sterile insect technique programmes requires a "production" orientated perspective, to deduce the most effective larval diet formulation; the information gained from this process offers us some insight into the mechanisms and processes taking place in natural native mosquito habitats.

Methodology/principal Findings: Fatty acid profiles and de-novo or direct assimilation pathways, of whole-individual mosquitoes reared on a range of larval diets were determined using pyrolysis gas chromatograph/mass spectrometry. We used elemental analysis and isotope ratio mass spectrometry to measure individual-whole-body carbon, nitrogen and phosphorous values and to assess the impact of dietary quality on subsequent population stoichiometry, size, quality and isotopic signature. Diet had the greatest impact on fatty acid (FA) profiles of the mosquitoes, which exhibited a high degree of dietary routing, characteristic of generalist feeders. De-novo synthesis of a number of important FAs was observed. Mosquito C:N stoichiometry was fixed in the teneral stage. Dietary N content had significant influence on mosquito size, and P was shown to be a flexible pool which limited overall population size.

Conclusions/significance: Direct routing of FAs was evident but there was ubiquitous de-novo synthesis suggesting mosquito larvae are competent generalist feeders capable of survival on diet with varying characteristics. It was concluded that nitrogen availability in the larval diet controlled teneral mosquito size and that teneral CN ratio is a sex- and species-specific fixed parameter. This finding has significant implications for overall mosquito competitiveness and environmental management.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0045222PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3484992PMC
May 2013

Intrinsic and synthetic stable isotope marking of tsetse flies.

J Insect Sci 2011 ;11:79

1 Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, International Atomic Energy Agency, Vienna, Austria.

The sterile insect technique has been successfully used to eliminate tsetse populations in a number of programs. Program monitoring in the field relies on the ability to accurately differentiate released sterile insects from wild insects so that estimates can be made of the ratio of sterile males to wild males. Typically, released flies are marked with a dye, which is not always reliable. The difference in isotopic signatures between wild and factory-reared populations could be a reliable and intrinsic secondary marker to complement existing marking methods. Isotopic signatures are natural differences in stable isotope composition of organisms due to discrimination against the heavier isotopes during some biological processes. As the isotopic signature of an organism is mainly dependent on what it eats; by feeding factory-reared flies isotopically different diets to those of the wild population it is possible to intrinsically mark the flies. To test this approach unlabeled samples of Glossina pallidipes (Austen) (Diptera: Glossinidae) from a mass rearing facility and wild populations were analyzed to determine whether there were any natural differences in signatures that could be used as markers. In addition experiments were conducted in which the blood diet was supplemented with isotopically enriched compounds and the persistence of the marker in the offspring determined. There were distinct natural isotopic differences between factory reared and wild tsetse populations that could be reliably used as population markers. It was also possible to rear artificially isotopically labeled flies using simple technology and these flies were clearly distinguishable from wild populations with greater than 95% certainty after 85 days of "release". These techniques could be readily adopted for use in SIT programs as complimentary marking techniques.
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http://dx.doi.org/10.1673/031.011.7901DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3281438PMC
November 2011
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