Publications by authors named "Meinhard Simon"

91 Publications

CAZymes in 62-1 From the Patagonian Shelf: Genomics and Physiology Compared to Related Flavobacteria and a Co-occurring Strain.

Front Microbiol 2021 12;12:628055. Epub 2021 Apr 12.

Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany.

Carbohydrate-active enzymes (CAZymes) are an important feature of bacteria in productive marine systems such as continental shelves, where phytoplankton and macroalgae produce diverse polysaccharides. We herein describe 62-1, a novel strain of this flavobacterial species, isolated from alginate-supplemented seawater collected at the Patagonian continental shelf. 62-1 harbors a diverse array of CAZymes in multiple polysaccharide utilization loci (PUL). Two PUL encoding polysaccharide lyases from families 6, 7, 12, and 17 allow substantial growth with alginate as sole carbon source, with simultaneous utilization of mannuronate and guluronate as demonstrated by HPLC. Furthermore, strain 62-1 harbors a mixed-feature PUL encoding both ulvan- and fucoidan-targeting CAZymes. Core-genome phylogeny and pangenome analysis revealed variable occurrence of these PUL in related and strains, indicating specialization to certain "polysaccharide niches." Furthermore, lineage- and strain-specific genomic signatures for exopolysaccharide synthesis possibly mediate distinct strategies for surface attachment and host interaction. The wide detection of CAZyme homologs in algae-derived metagenomes suggests global occurrence in algal holobionts, supported by sharing multiple adaptive features with the hydrolytic model flavobacterium . Comparison with sp. 76-1 isolated from the same seawater sample revealed that these co-occurring strains target similar polysaccharides but with different genomic repertoires, coincident with differing growth behavior on alginate that might mediate ecological specialization. Altogether, our study contributes to the perception of as versatile flavobacterial polysaccharide degrader, with implications for biogeochemical cycles, niche specialization and bacteria-algae interactions in the oceans.
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http://dx.doi.org/10.3389/fmicb.2021.628055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8072126PMC
April 2021

Sweet spheres: succession and CAZyme expression of marine bacterial communities colonizing a mix of alginate and pectin particles.

Environ Microbiol 2021 Apr 19. Epub 2021 Apr 19.

Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.

Polysaccharide particles are important substrates and microhabitats for marine bacteria. However, substrate-specific bacterial dynamics in mixtures of particle types with different polysaccharide composition, as likely occurring in natural habitats, are undescribed. Here, we studied the composition, functional diversity and gene expression of marine bacterial communities colonizing a mix of alginate and pectin particles. Amplicon, metagenome and metatranscriptome sequencing revealed that communities on alginate and pectin particles significantly differed from their free-living counterparts. Unexpectedly, microbial dynamics on alginate and pectin particles were similar, with predominance of amplicon sequence variants (ASVs) from Tenacibaculum, Colwellia, Psychrobium and Psychromonas. Corresponding metagenome-assembled genomes (MAGs) expressed diverse alginate lyases, several colocalized in polysaccharide utilization loci. Only a single, low-abundant MAG showed elevated transcript abundances of pectin-degrading enzymes. One specific Glaciecola ASV dominated the free-living fraction, possibly persisting on particle-derived oligomers through different glycoside hydrolases. Elevated ammonium uptake and metabolism signified nitrogen as an important factor for degrading carbon-rich particles, whereas elevated methylcitrate and glyoxylate cycles suggested nutrient limitation in surrounding waters. The bacterial preference for alginate, whereas pectin primarily served as colonization scaffold, illuminates substrate-driven dynamics within mixed polysaccharide pools. These insights expand our understanding of bacterial niche specialization and the biological carbon pump in macroalgae-rich habitats.
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http://dx.doi.org/10.1111/1462-2920.15536DOI Listing
April 2021

Lipidomic Analysis of Roseobacters of the Pelagic RCA Cluster and Their Response to Phosphorus Limitation.

Front Microbiol 2020 21;11:552135. Epub 2020 Dec 21.

School of Life Sciences, University of Warwick, Coventry, United Kingdom.

The marine roseobacter-clade affiliated cluster (RCA) represents one of the most abundant groups of bacterioplankton in the global oceans, particularly in temperate and sub-polar regions. They play a key role in the biogeochemical cycling of various elements and are important players in oceanic climate-active trace gas metabolism. In contrast to copiotrophic roseobacter counterparts such as DSS-3 and sp. MED193, RCA bacteria are truly pelagic and have smaller genomes. We have previously shown that RCA bacteria do not appear to encode the PlcP-mediated lipid remodeling pathway, whereby marine heterotrophic bacteria remodel their membrane lipid composition in response to phosphorus (P) stress by substituting membrane glycerophospholipids with alternative glycolipids or betaine lipids. In this study, we report lipidomic analysis of six RCA isolates. In addition to the commonly found glycerophospholipids such as phosphatidylglycerol (PG) and phosphatidylethanolamine (PE), RCA bacteria synthesize a relatively uncommon phospholipid, acylphosphatidylglycerol, which is not found in copiotrophic roseobacters. Instead, like the abundant SAR11 clade, RCA bacteria upregulate ornithine lipid biosynthesis in response to P stress, suggesting a key role of this aminolipid in the adaptation of marine heterotrophs to oceanic nutrient limitation.
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http://dx.doi.org/10.3389/fmicb.2020.552135DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7779409PMC
December 2020

Putative degraders of low-density polyethylene-derived compounds are ubiquitous members of plastic-associated bacterial communities in the marine environment.

Environ Microbiol 2020 11 28;22(11):4779-4793. Epub 2020 Sep 28.

Department of Functional and Evolutionary Ecology, University of Vienna, Vienna, Austria.

It remains unknown whether and to what extent marine prokaryotic communities are capable of degrading plastic in the ocean. To address this knowledge gap, we combined enrichment experiments employing low-density polyethylene (LDPE) as the sole carbon source with a comparison of bacterial communities on plastic debris in the Pacific, the North Atlantic and the northern Adriatic Sea. A total of 35 operational taxonomic units (OTUs) were enriched in the LDPE-laboratory incubations after 1 year, of which 20 were present with relative abundances > 0.5% in at least one plastic sample collected from the environment. From these, OTUs classified as Cognatiyoonia, Psychrobacter, Roseovarius and Roseobacter were found in the communities of plastics collected at all oceanic sites. Additionally, OTUs classified as Roseobacter, Pseudophaeobacter, Phaeobacter, Marinovum and Cognatiyoonia, also enriched in the LDPE-laboratory incubations, were enriched on LDPE communities compared to the ones associated to glass and polypropylene in in-situ incubations in the northern Adriatic Sea after 1 month of incubation. Some of these enriched OTUs were also related to known alkane and hydrocarbon degraders. Collectively, these results demonstrate that there are prokaryotes capable of surviving with LDPE as the sole carbon source living on plastics in relatively high abundances in different water masses of the global ocean.
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http://dx.doi.org/10.1111/1462-2920.15232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7702132PMC
November 2020

Genomic, metabolic and phenotypic variability shapes ecological differentiation and intraspecies interactions of Alteromonas macleodii.

Sci Rep 2020 01 21;10(1):809. Epub 2020 Jan 21.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

Ecological differentiation between strains of bacterial species is shaped by genomic and metabolic variability. However, connecting genotypes to ecological niches remains a major challenge. Here, we linked bacterial geno- and phenotypes by contextualizing pangenomic, exometabolomic and physiological evidence in twelve strains of the marine bacterium Alteromonas macleodii, illuminating adaptive strategies of carbon metabolism, microbial interactions, cellular communication and iron acquisition. In A. macleodii strain MIT1002, secretion of amino acids and the unique capacity for phenol degradation may promote associations with Prochlorococcus cyanobacteria. Strain 83-1 and three novel Pacific isolates, featuring clonal genomes despite originating from distant locations, have profound abilities for algal polysaccharide utilization but without detrimental implications for Ecklonia macroalgae. Degradation of toluene and xylene, mediated via a plasmid syntenic to terrestrial Pseudomonas, was unique to strain EZ55. Benzoate degradation by strain EC673 related to a chromosomal gene cluster shared with the plasmid of A. mediterranea EC615, underlining that mobile genetic elements drive adaptations. Furthermore, we revealed strain-specific production of siderophores and homoserine lactones, with implications for nutrient acquisition and cellular communication. Phenotypic variability corresponded to different competitiveness in co-culture and geographic distribution, indicating linkages between intraspecific diversity, microbial interactions and biogeography. The finding of "ecological microdiversity" helps understanding the widespread occurrence of A. macleodii and contributes to the interpretation of bacterial niche specialization, population ecology and biogeochemical roles.
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http://dx.doi.org/10.1038/s41598-020-57526-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6972757PMC
January 2020

Distinct relationships between fluorescence in situ hybridization and 16S rRNA gene- and amplicon-based sequencing data of bacterioplankton lineages.

Syst Appl Microbiol 2019 Sep 4;42(5):126000. Epub 2019 Jul 4.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Carl von Ossietzky Str. 9-11, D-26129 Oldenburg, Germany. Electronic address:

Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) and amplicon sequencing of the total (16S rRNA gene) and potentially active (16S rRNA transcripts), community are the major state of the art approaches for assessing the composition of bacterial communities in marine pelagic and other ecosystems. However, CARD-FISH and amplicon sequencing methods have not yet been directly compared to assess the composition of bacterioplankton communities. Therefore, these approaches were used to study the composition of bacterial communities in two North Sea seawater mesocosm experiments supplemented with diatom-derived organic matter (OM). All approaches revealed Proteobacteria and Bacteroidetes as major components of the bacterioplankton communities. The Roseobacter group and its RCA cluster, as well as Bacteroidetes and Gammaproteobacteria, responded most strongly to OM addition, whereas the SAR11 clade responded in only one of the two mesocosms. A correlation analysis showed that CARD-FISH and amplicon sequencing data of the SAR11 clade and the Roseobacter group, together with its RCA cluster, were highly significantly correlated, whereas Bacteroidetes did not yield any significant correlation and Gammaproteobacteria was only correlated with the potentially active fraction. However, subgroups of these phylogenetic groups, the SAR92 clade, the genera Pseudoalteromonas and Polaribacter, exhibited significant correlations in one of the two mesocosms. Correlations of CARD-FISH with amplicon sequencing data from the total and potentially active fractions of these lineages exhibited distinct differences. The study showed that CARD-FISH and amplicon sequencing data of distinct bacterioplankton groups and especially the phylogenetic lineages at a higher taxonomic level were correlated but reflected different aspects of their growth dynamics.
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http://dx.doi.org/10.1016/j.syapm.2019.06.005DOI Listing
September 2019

Complementary energy acquisition via aerobic anoxygenic photosynthesis and carbon monoxide oxidation by Planktomarina temperata of the Roseobacter group.

FEMS Microbiol Ecol 2019 05;95(5)

Institute of Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

In marine pelagic ecosystems energy is often the limiting factor for growth of heterotrophic bacteria. Aerobic anoxygenic photosynthesis (AAP) and oxidation of carbon monoxide (CO) are modes to acquire complementary energy, but their significance in abundant and characteristic pelagic marine bacteria has not been well studied. In long-term batch culture experiments we found that Planktomarina temperata RCA23, representing the largest and most prominent subcluster of the Roseobacter group, maintains 2-3-fold higher cell numbers in the stationary and declining phase when grown in a light-dark cycle relative to dark conditions. Light enables P. temperata to continue to replicate its DNA during the stationary phase relative to a dark control such that when reinoculated into fresh medium growth resumed two days earlier than in control cultures. In cultures grown in the dark and supplemented with CO, cell numbers in the stationary phase remained significantly higher than in an unsupplemented control. Furthermore, repeated spiking with CO until day 372 resulted in significant CO consumption relative to an unsupplemented control. P. temperata represents a prominent marine pelagic bacterium for which AAP and CO consumption, to acquire complementary energy, have been documented.
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http://dx.doi.org/10.1093/femsec/fiz050DOI Listing
May 2019

Phaeobacter inhibens controls bacterial community assembly on a marine diatom.

FEMS Microbiol Ecol 2019 06;95(6)

Centre for Marine Bio-Innovation and School of Biological, Earth and Environmental Sciences, The University of New South Wales Sydney, High street Randwick, NSW 2052, Australia.

Bacterial communities can have an important influence on the function of their eukaryotic hosts. However, how microbiomes are formed and the influence that specific bacteria have in shaping these communities is not well understood. Here, we used the marine diatom Thalassiosira rotula and the algal associated bacterium Phaeobacter inhibens as a model system to explore these questions. We exposed axenic (bacterial-free) T. rotula cultures to bacterial communities from natural seawater in the presence or absence of P. inhibens strain 2.10 or a variant strain (designated NCV12a1) that lacks antibacterial activity. We found that after 2 days the bacterial communities that assembled on the host were distinct from the free-living communities and comprised predominately of members of the Proteobacteria, Bacteroidetes and Cyanobacteria. In the presence of P. inhibens a higher abundance of Alphaproteobacteria, Flavobacteriia and Verrucomicrobia was detected. We also found only minor differences between the communities that established in the presence of either the wild type or the variant P. inhibens strain, suggesting that the antibacterial activity of P. inhibens is not the primary cause of its influence on bacterial community assembly. This study highlights the dynamic nature of algal microbiome development and the strong influence individual bacterial strains can have on this process.
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http://dx.doi.org/10.1093/femsec/fiz060DOI Listing
June 2019

Adaptations of sp. 76-1 to Polysaccharide Degradation: A CAZyme Plasmid for Ulvan Degradation and Two Alginolytic Systems.

Front Microbiol 2019 18;10:504. Epub 2019 Mar 18.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

Studying the physiology and genomics of cultured hydrolytic bacteria is a valuable approach to decipher the biogeochemical cycling of marine polysaccharides, major nutrients derived from phytoplankton and macroalgae. We herein describe the profound potential of sp. 76-1, isolated from alginate-enriched seawater at the Patagonian continental shelf, to degrade the algal polysaccharides alginate and ulvan. Phylogenetic analyses indicated that strain 76-1 might represent a novel species, distinguished from its closest relative () by adaptations to their contrasting habitats (productive open ocean vs. coastal sediments). Ecological distinction of 76-1 was particularly manifested in the abundance of carbohydrate-active enzymes (CAZymes), consistent with its isolation from alginate-enriched seawater and elevated abundance of a related OTU in the original microcosm. Strain 76-1 encodes multiple alginate lyases from families PL6, PL7, PL17, and PL18 largely contained in two polysaccharide utilization loci (PUL), which may facilitate the utilization of different alginate structures in nature. Notably, ulvan degradation relates to a 126 Kb plasmid dedicated to polysaccharide utilization, encoding several PL24 and PL25 ulvan lyases and monomer-processing genes. This extensive and versatile CAZyme repertoire allowed substantial growth on polysaccharides, showing comparable doubling times with alginate (2 h) and ulvan (3 h) in relation to glucose (3 h). The finding of homologous ulvanolytic systems in distantly related spp. suggests CAZyme plasmids as effective vehicles for PUL transfer that mediate niche gain. Overall, the demonstrated CAZyme repertoire substantiates the role of in marine polysaccharide degradation and how PUL exchange influences the ecophysiology of this ubiquitous marine taxon.
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http://dx.doi.org/10.3389/fmicb.2019.00504DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6431674PMC
March 2019

Does the Chemodiversity of Bacterial Exometabolomes Sustain the Chemodiversity of Marine Dissolved Organic Matter?

Front Microbiol 2019 14;10:215. Epub 2019 Feb 14.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

Marine dissolved organic matter (DOM) is a complex mixture of chemical compounds. At 750 Pg C, it is one of the biggest pools of reduced carbon on Earth. It has been proposed that the diversity of DOM is responsible for its recalcitrance. We hypothesize that the chemodiversity of marine DOM is a reflection of the chemodiversity of bacterial exometabolomes. To test this, we incubated two model strains of the group; and in pure culture using three different simple organic compounds as sole carbon sources (glutamate, glucose, and acetate and succinate for and , respectively). The exometabolome of the model organisms was characterized using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and ecological diversity measures. We detected thousands of molecular masses in the exometabolomes of and (21,105 and 9,386, respectively), reflecting the capability of single bacterial strains to diversify simple organic compounds. The chemical composition of the exometabolomes changed with growth phase and also differed according to the strain incubated and the utilized substrate. We mimicked a higher diversity of substrates, bacterial species and heterogeneous growth (different growth phases) to approach the complexity of natural environments, by computationally creating combinations of detected exometabolomes. We compared the chemodiversity of these combinations, indicative for chemodiversity of freshly produced microbial DOM to that of refractory DOM from one of the oldest oceanic water masses (North Equatorial Pacific Intermediate Water). Some combinations of exometabolomes showed higher richness than the deep ocean refractory DOM, and all the combinations showed higher functional diversity. About 15% of the 13,509 molecular formulae detected in exometabolomes and refractory oceanic DOM were shared, i.e., occurred in exometabolomes and in deep water samples. This overlap provides further support for our hypothesis that marine bacteria from the group contribute to the sustainability of marine DOM chemodiversity and stability.
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http://dx.doi.org/10.3389/fmicb.2019.00215DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6382689PMC
February 2019

Cobaviruses - a new globally distributed phage group infecting Rhodobacteraceae in marine ecosystems.

ISME J 2019 06 4;13(6):1404-1421. Epub 2019 Feb 4.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Carl-von-Ossietzky-Str. 9 -11, D-26111, Oldenburg, Germany.

Bacteriophages are widely considered to influence bacterial communities, however most phages are still unknown or not studied well enough to understand their ecological roles. We have isolated two phages infecting Lentibacter sp. SH36, affiliated with the marine Roseobacter group, and retrieved similar phage genomes from publicly available metagenomics databases. Phylogenetic analysis placed the new phages within the Cobavirus group, in the here newly proposed genus Siovirus and subfamily Riovirinae of the Podoviridae. Gene composition and presence of direct terminal repeats in cultivated cobaviruses point toward a genome replication and packaging strategy similar to the T7 phage. Investigation of the genomes suggests that viral lysis of the cell proceeds via the canonical holin-endolysin pathway. Cobaviral hosts include members of the genera Lentibacter, Sulfitobacter and Celeribacter of the Roseobacter group within the family Rhodobacteraceae (Alphaproteobacteria). Screening more than 5,000 marine metagenomes, we found cobaviruses worldwide from temperate to tropical waters, in the euphotic zone, mainly in bays and estuaries, but also in the open ocean. The presence of cobaviruses in protist metagenomes as well as the phylogenetic neighborhood of cobaviruses in glutaredoxin and ribonucleotide reductase trees suggest that cobaviruses could infect bacteria associated with phototrophic or grazing protists. With this study, we expand the understanding of the phylogeny, classification, genomic organization, biogeography and ecology of this phage group infecting marine Rhodobacteraceae.
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http://dx.doi.org/10.1038/s41396-019-0362-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6775973PMC
June 2019

Biphasic cellular adaptations and ecological implications of Alteromonas macleodii degrading a mixture of algal polysaccharides.

ISME J 2019 01 16;13(1):92-103. Epub 2018 Aug 16.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

Algal polysaccharides are an important bacterial nutrient source and central component of marine food webs. However, cellular and ecological aspects concerning the bacterial degradation of polysaccharide mixtures, as presumably abundant in natural habitats, are poorly understood. Here, we contextualize marine polysaccharide mixtures and their bacterial utilization in several ways using the model bacterium Alteromonas macleodii 83-1, which can degrade multiple algal polysaccharides and contributes to polysaccharide degradation in the oceans. Transcriptomic, proteomic and exometabolomic profiling revealed cellular adaptations of A. macleodii 83-1 when degrading a mix of laminarin, alginate and pectin. Strain 83-1 exhibited substrate prioritization driven by catabolite repression, with initial laminarin utilization followed by simultaneous alginate/pectin utilization. This biphasic phenotype coincided with pronounced shifts in gene expression, protein abundance and metabolite secretion, mainly involving CAZymes/polysaccharide utilization loci but also other functional traits. Distinct temporal changes in exometabolome composition, including the alginate/pectin-specific secretion of pyrroloquinoline quinone, suggest that substrate-dependent adaptations influence chemical interactions within the community. The ecological relevance of cellular adaptations was underlined by molecular evidence that common marine macroalgae, in particular Saccharina and Fucus, release mixtures of alginate and pectin-like rhamnogalacturonan. Moreover, CAZyme microdiversity and the genomic predisposition towards polysaccharide mixtures among Alteromonas spp. suggest polysaccharide-related traits as an ecophysiological factor, potentially relating to distinct 'carbohydrate utilization types' with different ecological strategies. Considering the substantial primary productivity of algae on global scales, these insights contribute to the understanding of bacteria-algae interactions and the remineralization of chemically diverse polysaccharide pools, a key step in marine carbon cycling.
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http://dx.doi.org/10.1038/s41396-018-0252-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6298977PMC
January 2019

Distinct biogeographic patterns of bacterioplankton composition and single-cell activity between the subtropics and Antarctica.

Environ Microbiol 2018 08 9;20(8):3100-3108. Epub 2018 Sep 9.

Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany.

Bacterial biogeography and activity in the Southern Ocean are poorly understood to date. Here, we applied CARD-FISH to quantify bacterial community structure from the subtropics to Antarctica between 10°W and 10°E, covering four biogeographic provinces with distinct environmental properties. In addition, incorporation of radiolabeled glucose, amino acids and leucine via MAR-FISH served to quantify the contribution to substrate turnover by selected bacterial groups. SAR11, Bacteroidetes, Gammaproteobacteria and the Roseobacter group accounted for the majority of the bacterial community (52%-88% of DAPI-stained cells) but showed little distributional variation between provinces. In contrast, taxonomic subclades Polaribacter, NS5, NS2b (Bacteroidetes) as well as RCA (Roseobacter group) featured marked geographic variation, illustrated by NMDS and coefficients of variation. Roseobacter (specifically RCA) and Gammaproteobacteria constituted considerable fractions of cells incorporating glucose and amino acids respectively. Bacteroidetes had generally lower activities, but Polaribacter accounted for a major fraction of biomass production at one station near the Antarctic ice shelf. In conclusion, distributional patterns at finer taxonomic level and highest substrate turnover by less abundant taxa highlight the importance of taxonomic subclades in marine carbon fluxes, contributing to the understanding of functional bacterial biogeography in the Southern Ocean.
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http://dx.doi.org/10.1111/1462-2920.14383DOI Listing
August 2018

Editorial: Molecular Ecology and Genetic Diversity of the Clade.

Front Microbiol 2018 1;9:1185. Epub 2018 Jun 1.

Genomic and Applied Microbiology and Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, University of Göttingen, Göttingen, Germany.

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http://dx.doi.org/10.3389/fmicb.2018.01185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992283PMC
June 2018

Genome sequence of type strain (SH6-1), a representative of the group isolated from the North Sea during a phytoplankton bloom.

Stand Genomic Sci 2018 11;13. Epub 2018 Apr 11.

1Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, Germany.

SH6-1 Hahnke et al. (Int J Syst Evol Microbiol 62:1619-24, 2012) is a planktonic marine bacterium isolated during a phytoplankton bloom from the southern North Sea. It belongs to the group within the alphaproteobacterial family . Here we describe the draft genome sequence and annotation of the type strain SH6-1. The genome comprises 4,106,736 bp and contains 4128 protein-coding and 38 RNA genes. The draft genome sequence provides evidence for at least three extrachromosomal elements, encodes genes for DMSP utilization, quorum sensing, photoheterotrophy and a type IV secretion system. This indicates not only adaptation to a free-living lifestyle of but points also to interactions with prokaryotic or eukaryotic organisms.
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http://dx.doi.org/10.1186/s40793-018-0311-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5896138PMC
April 2018

Tritonibacter horizontis gen. nov., sp. nov., a member of the Rhodobacteraceae, isolated from the Deepwater Horizon oil spill.

Int J Syst Evol Microbiol 2018 Mar 6;68(3):736-744. Epub 2018 Feb 6.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, D-26111 Oldenburg, Germany.

A heterotrophic, Gram-stain-negative, aerobic, sodium-requiring and motile bacterium was isolated from oil-contaminated surface water of the Gulf of Mexico during the Deepwater Horizon oil spill. Strain O3.65 showed highest 16S rRNA gene sequence similarity to Phaeobacter gallaeciensis BS107 and Phaeobacter inhibens T5, both with 98.3 %, respectively. Based on complete genome analysis, highest similarity was observed to species of the genus Ruegeria. Strain O3.65 exhibited a broad salinity, temperature and pH range of 0.5-10 % NaCl, 4-45 °C and 5.5-9.0, respectively. The DNA G+C content of strain O3.65 was 61.5 mol%. The major respiratory lipoquinone was ubiquinone-10 (Q-10), the most dominant fatty acids (>1 %) comprised 18 : 1ω7c and 18 : 1ω7c 11-methyl, 10 : 0 3OH, 12 : 1 3OH, 14 : 1 3OH/3-oxo-14 : 0, 16 : 0, 16 : 0 2OH, 18 : 1 2OH and 12 : 1. The polar lipid pattern indicated presence of phosphatidylcholine, phosphatidylglycerol, an unidentified aminolipid, two unidentified phospholipids and seven unidentified lipids. On Difco marine broth agar, strain O3.65 formed smooth, shiny white to beige and convex colonies with regular edges. Phylogenetic, phylogenomic and phenotypic differences revealed that strain O3.65 represents a new species of a novel genus within the family Rhodobacteraceae, for which we propose the name Tritonibacter horizontis gen. nov., sp. nov. The type strain of the type species is O3.65 (=DSM 101689=LMG 29740).
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http://dx.doi.org/10.1099/ijsem.0.002573DOI Listing
March 2018

Linking Compositional and Functional Predictions to Decipher the Biogeochemical Significance in DFAA Turnover of Abundant Bacterioplankton Lineages in the North Sea.

Microorganisms 2017 Nov 5;5(4). Epub 2017 Nov 5.

Institute of Microbiology and Genetics, University of Göttingen, Grisebachstr. 8, D-37077 Göttingen, Germany.

Deciphering the ecological traits of abundant marine bacteria is a major challenge in marine microbial ecology. In the current study, we linked compositional and functional predictions to elucidate such traits for abundant bacterioplankton lineages in the North Sea. For this purpose, we investigated entire and active bacterioplankton composition along a transect ranging from the German Bight to the northern North Sea by pyrotag sequencing of bacterial 16S rRNA genes and transcripts. Functional profiles were inferred from 16S rRNA data using Tax4Fun. Bacterioplankton communities were dominated by well-known marine lineages including clusters/genera that are affiliated with the group and the . Variations in community composition and function were significantly explained by measured environmental and microbial properties. Turnover of dissolved free amino acids (DFAA) showed the strongest correlation to community composition and function. We applied multinomial models, which enabled us to identify bacterial lineages involved in DFAA turnover. For instance, the genus was more abundant at higher DFAA turnover rates, suggesting its vital role in amino acid degradation. Functional predictions further indicated that is involved in leucine and isoleucine degradation. Overall, our results provide novel insights into the biogeochemical significance of abundant bacterioplankton lineages in the North Sea.
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http://dx.doi.org/10.3390/microorganisms5040068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5748577PMC
November 2017

The Exometabolome of Two Model Strains of the Group: A Marketplace of Microbial Metabolites.

Front Microbiol 2017 12;8:1985. Epub 2017 Oct 12.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany.

Recent studies applying Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) showed that the exometabolome of marine bacteria is composed of a surprisingly high molecular diversity. To shed more light on how this diversity is generated we examined the exometabolome of two model strains of the group, and , grown on glutamate, glucose, acetate or succinate by FT-ICR-MS. We detected 2,767 and 3,354 molecular formulas in the exometabolome of each strain and 67 and 84 matched genome-predicted metabolites of and , respectively. The annotated compounds include late precursors of biosynthetic pathways of vitamins B, B, B, B, B, B, amino acids, quorum sensing-related compounds, indole acetic acid and methyl-(indole-3-yl) acetic acid. Several formulas were also found in phytoplankton blooms. To shed more light on the effects of some of the precursors we supplemented two B prototrophic diatoms with the detected precursor of vitamin B HET (4-methyl-5-(β-hydroxyethyl)thiazole) and HMP (4-amino-5-hydroxymethyl-2-methylpyrimidine) and found that their growth was stimulated. Our findings indicate that both strains and other bacteria excreting a similar wealth of metabolites may function as important helpers to auxotrophic and prototrophic marine microbes by supplying growth factors and biosynthetic precursors.
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http://dx.doi.org/10.3389/fmicb.2017.01985DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5643483PMC
October 2017

Composition of Total and Cell-Proliferating Bacterioplankton Community in Early Summer in the North Sea - Roseobacters Are the Most Active Component.

Front Microbiol 2017 13;8:1771. Epub 2017 Sep 13.

Institute for Chemistry and Biology of the Marine Environment, University of OldenburgOldenburg, Germany.

Heterotrophic bacterioplankton communities play an important role in organic matter processing in the oceans worldwide. In order to investigate the significance of distinct phylogenetic bacterial groups it is not only important to assess their quantitative abundance but also their growth dynamics in relation to the entire bacterioplankton. Therefore bacterial abundance, biomass production and the composition of the entire and cell-proliferating bacterioplankton community were assessed in North Sea surface waters between the German Bight and 58°N in early summer by applying catalyzed reporter deposition (CARD-FISH) and bromodeoxyuridine fluorescence hybridization (BrdU-FISH). and the group dominated the cell-proliferating fraction with 10-55 and 8-31% of total BrdU-positive cells, respectively. While also showed high abundances in the total bacterial fraction, roseobacters constituted only 1-9% of all cells. Despite abundances of up to 55% of total bacterial cells, the SAR11 clade constituted <6% of BrdU-positive cells. accounted for 2-16% of the total and 2-13% of the cell-proliferating cells. Within the two most active groups, BrdU-positive cells made up 28% of as an overall mean and 36% of roseobacters. Estimated mean growth rates of and the group were 1.2 and 1.5 day, respectively, and much higher than bulk growth rates of the bacterioplankton whereas those of the SAR11 clade and were 0.04 and 0.21 day, respectively, and much lower than bulk growth rates. Only numbers of total and cell-proliferating roseobacters but not those of and the other groups were significantly correlated to chlorophyll fluorescence and bacterioplankton biomass production. The group, besides , appeared to be a major player in processing phytoplankton derived organic matter despite its low partitioning in the total bacterioplankton community.
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http://dx.doi.org/10.3389/fmicb.2017.01771DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5604061PMC
September 2017

Marine microbiology: Roommates in space and time.

Authors:
Meinhard Simon

Nat Microbiol 2017 08 24;2:17122. Epub 2017 Aug 24.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, D-26111 Oldenburg, Germany.

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http://dx.doi.org/10.1038/nmicrobiol.2017.122DOI Listing
August 2017

Phaeobacter porticola sp. nov., an antibiotic-producing bacterium isolated from a sea harbour.

Int J Syst Evol Microbiol 2017 Jul 12;67(7):2153-2159. Epub 2017 Jul 12.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany.

Three heterotrophic, aerobic, brown-pigmented strains, designated P97T, P100 and P104, were isolated from a harbour in the southern North Sea. Phylogenetic analysis of 16S rRNA gene sequences revealed that the isolates are affiliated to the genus Phaeobacter. In silico DNA-DNA hybridization of the genome of strain P97T against those of existing type species indicated that P97T represents a novel species within the genus Phaeobacter, with Phaeobacter inhibens T5T as the closest described organism (29.6 % DNA-DNA relatedness) followed by P. gallaeciensis CIP 105210T (26.4 %). DNA-DNA hybridization demonstrated that the three new strains belong to the same species. The new isolates inhibited Pseudoalteromonas tunicata DSM 14096T, and were Gram-stain-negative, catalase- and oxidase-positive, chemo-organoheterotrophic and motile. Growth occurred at pH 6.5-9.5 (optimum 7.0-8.0) and at 4-30 °C (optimum 20-28 °C). The strains required NaCl for growth. The salinity range was 0.5-6.0 % (w/v) NaCl for P97T and P100, and 0.5-5.0 % for P104, lower than values described for Phaeobacter gallaeciensis and Phaeobacter inhibens. The optimum NaCl concentration for strains P97T and P104 was 2.0-4.0 %, and for P100 was 2.0-3.0 %. Fatty acids (>1 %) comprised 18 : 1ω7c, 16 : 0, 18 : 1 ω7c 11-methyl, 18 : 0, 12 :1, 18 : 2ω7c,12, 10 : 0 3-OH and 12 : 0 3-OH. Polar lipids were phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an aminolipid, one unknown lipid and one additional unknown lipid in strain P97T. The major respiratory quinone was Q10. Based on phylogenetic and phenotypic differences, the strains represent a novel species in the genus Phaeobacter, for which the name Phaeobacter porticola sp. nov. is proposed. The type strain is P97T (=DSM 103148T=LMG 29594T).
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http://dx.doi.org/10.1099/ijsem.0.001879DOI Listing
July 2017

Rhodobacteraceae on the marine brown alga Fucus spiralis are abundant and show physiological adaptation to an epiphytic lifestyle.

Syst Appl Microbiol 2017 Sep 15;40(6):370-382. Epub 2017 Jun 15.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg, Germany. Electronic address:

Macroalgae harbour specific microbial communities on their surface that have functions related to host health and defence. In this study, the bacterial biofilm of the marine brown alga Fucus spiralis was investigated using 16S rRNA gene amplicon-based analysis and isolation of bacteria. Rhodobacteraceae (Alphaproteobacteria) were the predominant family constituting 23% of the epibacterial community. At the genus level, Sulfitobacter, Loktanella, Octadecabacter and a previously undescribed cluster were most abundant, and together they comprised 89% of the Rhodobacteraceae. Supported by a specific PCR approach, 23 different Rhodobacteraceae-affiliated strains were isolated from the surface of F. spiralis, which belonged to 12 established and three new genera. For seven strains, closely related sequences were detected in the 16S rRNA gene dataset. Growth experiments with substrates known to be produced by Fucus spp. showed that all of them were consumed by at least three strains, and vitamin B was produced by 70% of the isolates. Since growth of F. spiralis depends on B supplementation, bacteria may provide the alga with this vitamin. Most strains produced siderophores, which can enhance algal growth under iron-deficient conditions. Inhibiting properties against other bacteria were only observed when F. spiralis material was present in the medium. Thus, the physiological properties of the isolates indicated adaption to an epiphytic lifestyle.
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http://dx.doi.org/10.1016/j.syapm.2017.05.006DOI Listing
September 2017

Dual function of tropodithietic acid as antibiotic and signaling molecule in global gene regulation of the probiotic bacterium Phaeobacter inhibens.

Sci Rep 2017 04 7;7(1):730. Epub 2017 Apr 7.

Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, 26129, Oldenburg, Germany.

Antibiotics are typically regarded as microbial weapons, but whereas their function at concentrations lethal for bacteria is often well characterized, the role of antibiotics at much lower concentrations as possibly found under natural conditions remains poorly understood. By using whole-transcriptome analyses and phenotypic screenings of the marine bacterium Phaeobacter inhibens we found that the broad-spectrum antibiotic tropodithietic acid (TDA) causes the same regulatory effects in quorum sensing (QS) as the common signaling molecule N-acyl-homoserine lactone (AHL) at concentrations 100-fold lower than the minimal inhibitory concentration against bacteria. Our results show that TDA has a significant impact on the expression of ~10% of the total genes of P. inhibens, in the same manner as the AHL. Furthermore, TDA needs the AHL associated LuxR-type transcriptional regulator, just as the AHL molecule. Low concentrations of antibiotics can obviously have a strong influence on the global gene expression of the bacterium that produces it and drastically change the metabolism and behaviour of the bacterium. For P. inhibens this includes motility, biofilm formation and antibiotic production, all important for settlement on new host-associated surfaces. Our results demonstrate that bacteria can produce antibiotics not only to antagonise other bacteria, but also to mediate QS like endogenous AHL molecules.
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http://dx.doi.org/10.1038/s41598-017-00784-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5429656PMC
April 2017

Phylogenomics of Rhodobacteraceae reveals evolutionary adaptation to marine and non-marine habitats.

ISME J 2017 06 20;11(6):1483-1499. Epub 2017 Jan 20.

Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany.

Marine Rhodobacteraceae (Alphaproteobacteria) are key players of biogeochemical cycling, comprise up to 30% of bacterial communities in pelagic environments and are often mutualists of eukaryotes. As 'Roseobacter clade', these 'roseobacters' are assumed to be monophyletic, but non-marine Rhodobacteraceae have not yet been included in phylogenomic analyses. Therefore, we analysed 106 genome sequences, particularly emphasizing gene sampling and its effect on phylogenetic stability, and investigated relationships between marine versus non-marine habitat, evolutionary origin and genomic adaptations. Our analyses, providing no unequivocal evidence for the monophyly of roseobacters, indicate several shifts between marine and non-marine habitats that occurred independently and were accompanied by characteristic changes in genomic content of orthologs, enzymes and metabolic pathways. Non-marine Rhodobacteraceae gained high-affinity transporters to cope with much lower sulphate concentrations and lost genes related to the reduced sodium chloride and organohalogen concentrations in their habitats. Marine Rhodobacteraceae gained genes required for fucoidan desulphonation and synthesis of the plant hormone indole 3-acetic acid and the compatible solutes ectoin and carnitin. However, neither plasmid composition, even though typical for the family, nor the degree of oligotrophy shows a systematic difference between marine and non-marine Rhodobacteraceae. We suggest the operational term 'Roseobacter group' for the marine Rhodobacteraceae strains.
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http://dx.doi.org/10.1038/ismej.2016.198DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437341PMC
June 2017

Biogeography and environmental genomics of the Roseobacter-affiliated pelagic CHAB-I-5 lineage.

Nat Microbiol 2016 05 16;1(7):16063. Epub 2016 May 16.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Oldenburg D-26111, Germany.

The identification and functional characterization of microbial communities remains a prevailing topic in microbial oceanography as information on environmentally relevant pelagic prokaryotes is still limited. The Roseobacter group, an abundant lineage of marine Alphaproteobacteria, can constitute large proportions of the bacterioplankton. Roseobacters also occur associated with eukaryotic organisms and possess streamlined as well as larger genomes from 2.2 to >5 Mpb. Here, we show that one pelagic cluster of this group, CHAB-I-5, occurs globally from tropical to polar regions and accounts for up to 22% of the active North Sea bacterioplankton in the summer. The first sequenced genome of a CHAB-I-5 organism comprises 3.6 Mbp and exhibits features of an oligotrophic lifestyle. In a metatranscriptome of North Sea surface waters, 98% of the encoded genes were present, and genes encoding various ABC transporters, glutamate synthase and CO oxidation were particularly upregulated. Phylogenetic gene content analyses of 41 genomes of the Roseobacter group revealed a unique cluster of pelagic organisms distinct from other lineages of this group, highlighting the adaptation to life in nutrient-depleted environments.
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http://dx.doi.org/10.1038/nmicrobiol.2016.63DOI Listing
May 2016

A novel roseobacter phage possesses features of podoviruses, siphoviruses, prophages and gene transfer agents.

Sci Rep 2016 07 27;6:30372. Epub 2016 Jul 27.

Institution of Marine and Environmental Technology, University of Maryland Center for Environmental Science, USA.

Bacteria in the Roseobacter lineage have been studied extensively due to their significant biogeochemical roles in the marine ecosystem. However, our knowledge on bacteriophage which infects the Roseobacter clade is still very limited. Here, we report a new bacteriophage, phage DSS3Φ8, which infects marine roseobacter Ruegeria pomeroyi DSS-3. DSS3Φ8 is a lytic siphovirus. Genomic analysis showed that DSS3Φ8 is most closely related to a group of siphoviruses, CbK-like phages, which infect freshwater bacterium Caulobacter crescentus. DSS3Φ8 contains a smaller capsid and has a reduced genome size (146 kb) compared to the CbK-like phages (205-279 kb). DSS3Φ8 contains the DNA polymerase gene which is closely related to T7-like podoviruses. DSS3Φ8 also contains the integrase and repressor genes, indicating its potential to involve in lysogenic cycle. In addition, four GTA (gene transfer agent) genes were identified in the DSS3Φ8 genome. Genomic analysis suggests that DSS3Φ8 is a highly mosaic phage that inherits the genetic features from siphoviruses, podoviruses, prophages and GTAs. This is the first report of CbK-like phages infecting marine bacteria. We believe phage isolation is still a powerful tool that can lead to discovery of new phages and help interpret the overwhelming unknown sequences in the viral metagenomics.
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http://dx.doi.org/10.1038/srep30372DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4961962PMC
July 2016

Co-occurrence Analysis of Microbial Taxa in the Atlantic Ocean Reveals High Connectivity in the Free-Living Bacterioplankton.

Front Microbiol 2016 6;7:649. Epub 2016 May 6.

Group Microbial Communication, Helmholtz-Center for Infection Research Braunschweig, Germany.

We determined the taxonomic composition of the bacterioplankton of the epipelagic zone of the Atlantic Ocean along a latitudinal transect (51°S-47°N) using Illumina sequencing of the V5-V6 region of the 16S rRNA gene and inferred co-occurrence networks. Bacterioplankon community composition was distinct for Longhurstian provinces and water depth. Free-living microbial communities (between 0.22 and 3 μm) were dominated by highly abundant and ubiquitous taxa with streamlined genomes (e.g., SAR11, SAR86, OM1, Prochlorococcus) and could clearly be separated from particle-associated communities which were dominated by Bacteroidetes, Planktomycetes, Verrucomicrobia, and Roseobacters. From a total of 369 different communities we then inferred co-occurrence networks for each size fraction and depth layer of the plankton between bacteria and between bacteria and phototrophic micro-eukaryotes. The inferred networks showed a reduction of edges in the deepest layer of the photic zone. Networks comprised of free-living bacteria had a larger amount of connections per OTU when compared to the particle associated communities throughout the water column. Negative correlations accounted for roughly one third of the total edges in the free-living communities at all depths, while they decreased with depth in the particle associated communities where they amounted for roughly 10% of the total in the last part of the epipelagic zone. Co-occurrence networks of bacteria with phototrophic micro-eukaryotes were not taxon-specific, and dominated by mutual exclusion (~60%). The data show a high degree of specialization to micro-environments in the water column and highlight the importance of interdependencies particularly between free-living bacteria in the upper layers of the epipelagic zone.
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http://dx.doi.org/10.3389/fmicb.2016.00649DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4858663PMC
May 2016

Bacterioplankton Biogeography of the Atlantic Ocean: A Case Study of the Distance-Decay Relationship.

Front Microbiol 2016 26;7:590. Epub 2016 Apr 26.

Group Microbial Communication, Helmholtz-Center for Infection Research Braunschweig, Germany.

In order to determine the influence of geographical distance, depth, and Longhurstian province on bacterial community composition and compare it with the composition of photosynthetic micro-eukaryote communities, 382 samples from a depth-resolved latitudinal transect (51°S-47°N) from the epipelagic zone of the Atlantic ocean were analyzed by Illumina amplicon sequencing. In the upper 100 m of the ocean, community similarity decreased toward the equator for 6000 km, but subsequently increased again, reaching similarity values of 40-60% for samples that were separated by ~12,000 km, resulting in a U-shaped distance-decay curve. We conclude that adaptation to local conditions can override the linear distance-decay relationship in the upper epipelagial of the Atlantic Ocean which is apparently not restrained by barriers to dispersal, since the same taxa were shared between the most distant communities. The six Longhurstian provinces covered by the transect were comprised of distinct microbial communities; ~30% of variation in community composition could be explained by province. Bacterial communities belonging to the deeper layer of the epipelagic zone (140-200 m) lacked a distance-decay relationship altogether and showed little provincialism. Interestingly, those biogeographical patterns were consistently found for bacteria from three different size fractions of the plankton with different taxonomic composition, indicating conserved underlying mechanisms. Analysis of the chloroplast 16S rRNA gene sequences revealed that phytoplankton composition was strongly correlated with both free-living and particle associated bacterial community composition (R between 0.51 and 0.62, p < 0.002). The data show that biogeographical patterns commonly found in macroecology do not hold for marine bacterioplankton, most likely because dispersal and evolution occur at drastically different rates in bacteria.
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http://dx.doi.org/10.3389/fmicb.2016.00590DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4845060PMC
May 2016

Dimethylsulfoniopropionate Promotes Process Outgrowth in Neural Cells and Exerts Protective Effects against Tropodithietic Acid.

Mar Drugs 2016 May 6;14(5). Epub 2016 May 6.

Molecular Neurobiology, Department of Neurosciences, University of Oldenburg, Oldenburg 26111, Germany.

The marine environment harbors a plethora of bioactive substances, including drug candidates of potential value in the field of neuroscience. The present study was undertaken to investigate the effects of dimethylsulfoniopropionate (DMSP), produced by several algae, corals and higher plants, on cells of the mammalian nervous system, i.e., neuronal N2a and OLN-93 cells as model system for nerve cells and glia, respectively. Additionally, the protective capabilities of DMSP were assessed in cells treated with tropodithietic acid (TDA), a marine metabolite produced by several Roseobacter clade bacteria. Both cell lines, N2a and OLN-93, have previously been shown to be a sensitive target for the action of TDA, and cytotoxic effects of TDA have been connected to the induction of oxidative stress. Our data shows that DMSP promotes process outgrowth and microtubule reorganization and bundling, accompanied by an increase in alpha-tubulin acetylation. Furthermore, DMSP was able to prevent the cytotoxic effects exerted by TDA, including the breakdown of the mitochondrial membrane potential, upregulation of heat shock protein Hsp32 and activation of the extracellular signal-regulated kinases 1/2 (ERK1/2). Our study points to the conclusion that DMSP provides an antioxidant defense, not only in algae but also in mammalian neural cells.
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http://dx.doi.org/10.3390/md14050089DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4882563PMC
May 2016

Response of bacterial communities from California coastal waters to alginate particles and an alginolytic Alteromonas macleodii strain.

Environ Microbiol 2016 12 30;18(12):4369-4377. Epub 2016 May 30.

Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26129 Oldenburg, Germany.

Alginate is a major cell wall polysaccharide from marine macroalgae and nutrient source for heterotrophic bacteria. Alginate can form gel particles in contact with divalent cations as found in seawater. Here, we tested the hypothesis that alginate gel particles serve as carbon source and microhabitat for marine bacteria by adding sterile alginate particles to microcosms with seawater from coastal California, a habitat rich in alginate-containing macroalgae. Alginate particles were rapidly colonized and degraded, with three- to eightfold higher bacterial abundances and production among alginate particle-associated (PA) bacteria. 16S rRNA gene amplicon sequencing showed that alginate PA bacteria were enriched in OTUs related to Cryomorphaceae, Saprospiraceae (Bacteroidetes) and Phaeobacter (Alphaproteobacteria) towards the end of the experiment. In microcosms amended with alginate particles and the proficient alginolytic bacterium Alteromonas macleodii strain 83-1, this strain dominated the community and outcompeted Cryomorphaceae, Saprospiraceae and Phaeobacter, and PA hydrolytic activities were over 50% higher. Thus, alginolytic activity by strain 83-1 did not benefit non-alginolytic strains by cross-feeding on alginate hydrolysis or other metabolic products. Considering the global distribution and extensive biomass of alginate-containing macroalgae, the observed bacterial dynamics associated with the utilization and remineralization of alginate microhabitats promote the understanding of carbon cycling in macroalgae-rich waters worldwide.
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http://dx.doi.org/10.1111/1462-2920.13314DOI Listing
December 2016