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Summary: Sulphide‐driven anoxygenic photosynthesis is an ancient microbial metabolism that contributes significantly to inorganic carbon fixation in stratified, sulphidic water bodies. Methods commonly applied to quantify inorganic carbon fixation by anoxygenic phototrophs, however, cannot resolve the contributions of distinct microbial populations to the overall process. We implemented a straightforward workflow, consisting of radioisotope labelling and flow cytometric cell sorting based on the distinct autofluorescence of bacterial photopigments, to discriminate and quantify contributions of co‐occurring anoxygenic phototrophic populations to in situ inorganic carbon fixation in environmental samples. This allowed us to assign 89.3% ± 7.6% of daytime inorganic carbon fixation by anoxygenic phototrophs in Lake Rogoznica (Croatia) to an abundant chemocline‐dwelling population of green sulphur bacteria (dominated by Chlorobium phaeobacteroides), whereas the co‐occurring purple sulphur bacteria (Halochromatium sp.) contributed only 1.8% ± 1.4%. Furthermore, we obtained two metagenome assembled genomes of green sulphur bacteria and one of a purple sulphur bacterium which provides the first genomic insights into the genus Halochromatium, confirming its high metabolic flexibility and physiological potential for mixo‐ and heterotrophic growth. [ABSTRACT FROM AUTHOR]

Summary: Chemoautotrophic bacteria belonging to the genus Sulfurimonas (class Campylobacteria) were previously identified as key players in the turnover of zero‐valence sulfur, a central intermediate in the marine sulfur cycle. S. denitrificans was further shown to be able to oxidize cyclooctasulfur (S8). However, at present the mechanism of activation and metabolism of cyclooctasulfur is not known. Here, we assessed the transcriptome and proteome of S. denitrificans grown with either thiosulfate or S8 as the electron donor. While the overall expression profiles under the two growth conditions were rather similar, distinct differences were observed that could be attributed to the utilization of S8. This included a higher abundance of expressed genes related to surface attachment in the presence of S8, and the differential regulation of the sulfur‐oxidation multienzyme complex (SOX), which in S. denitrificans is encoded in two gene clusters: soxABXY1Z1 and soxCDY2Z2. While the proteins of both clusters were present with thiosulfate, only proteins of the soxCDY2Z2 were detected at significant levels with S8. Based on these findings a model for the oxidation of S8 is proposed. Our results have implications for interpreting metatranscriptomic and ‐proteomic data and for the observed high level of diversification of soxY2Z2 among sulfur‐oxidizing Campylobacteria. [ABSTRACT FROM AUTHOR]

Summary: Molecular hydrogen (H2) is the key intermediate in the anaerobic degradation of organic matter. Its removal by H2‐oxidizing microorganisms is essential to keep anaerobic degradation energetically favourable. Sulfate‐reducing microorganisms (SRM) are known as the main H2 scavengers in anoxic marine sediments. Although the community of marine SRM has been extensively studied, those consuming H2in situ are completely unknown. We combined metagenomics, PCR‐based clone libraries, single‐amplified genomes (SAGs) and metatranscriptomics to identify potentially H2‐consuming SRM in anoxic coastal sediments. The vast majority of SRM‐related H2ase sequences were assigned to group 1b and 1c [NiFe]‐H2ases of the deltaproteobacterial order Desulfobacterales. Surprisingly, the same sequence types were similarly highly expressed in spring and summer, suggesting that these are stable and integral members of the H2‐consuming community. Notably, one sequence cluster from the SRM group 1 consistently accounted for around half of all [NiFe]‐H2ase transcripts. Using SAGs, we could link this cluster with the 16S rRNA genes of the uncultured Sva0081‐group of the family Desulfobacteraceae. Sequencing of 16S rRNA gene amplicons and H2ase gene libraries suggested consistently high in situ abundance of the Sva0081 group also in other marine sediments. Together with other Desulfobacterales these likely are important H2‐scavengers in marine sediments. [ABSTRACT FROM AUTHOR]

Molecular hydrogen (H 2 ) is the key intermediate in the anaerobic degradation of organic matter. Its removal by H 2 -oxidizing microorganisms is essential to keep anaerobic degradation energetically favourable. Sulfate-reducing microorganisms (SRM) are known as the main H 2 scavengers in anoxic marine sediments. Although the community of marine SRM has been extensively studied, those consuming H 2 in situ are completely unknown. We combined metagenomics, PCR-based clone libraries, single-amplified genomes (SAGs) and metatranscriptomics to identify potentially H 2 -consuming SRM in anoxic coastal sediments. The vast majority of SRM-related H 2 ase sequences were assigned to group 1b and 1c [NiFe]-H 2 ases of the deltaproteobacterial order Desulfobacterales. Surprisingly, the same sequence types were similarly highly expressed in spring and summer, suggesting that these are stable and integral members of the H 2 -consuming community. Notably, one sequence cluster from the SRM group 1 consistently accounted for around half of all [NiFe]-H 2 ase transcripts. Using SAGs, we could link this cluster with the 16S rRNA genes of the uncultured Sva0081-group of the family Desulfobacteraceae. Sequencing of 16S rRNA gene amplicons and H 2 ase gene libraries suggested consistently high in situ abundance of the Sva0081 group also in other marine sediments. Together with other Desulfobacterales these likely are important H 2 -scavengers in marine sediments., (© 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.)