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Sulfate/sulfite-reducing microorganisms (SRM) are ubiquitous in nature, driving the global sulfur cycle. A hallmark of SRM is the dissimilatory sulfite reductase encoded by the genes dsrAB. Based on analysis of 950 mainly metagenome-derived dsrAB -carrying genomes, we redefine the global diversity of microorganisms with the potential for dissimilatory sulfate/sulfite reduction and uncover genetic repertoires that challenge earlier generalizations regarding their mode of energy metabolism. We show: (i) 19 out of 23 bacterial and 2 out of 4 archaeal phyla harbor uncharacterized SRM, (ii) four phyla including the Desulfobacterota harbor microorganisms with the genetic potential to switch between sulfate/sulfite reduction and sulfur oxidation, and (iii) the combination as well as presence/absence of different dsrAB- types , dsrL -types and dsrD provides guidance on the inferred direction of dissimilatory sulfur metabolism. We further provide an updated dsrAB database including > 60% taxonomically resolved, uncultured family-level lineages and recommendations on existing dsrAB -targeted primers for environmental surveys. Our work summarizes insights into the inferred ecophysiology of newly discovered SRM, puts SRM diversity into context of the major recent changes in bacterial and archaeal taxonomy, and provides an up-to-date framework to study SRM in a global context. [ABSTRACT FROM AUTHOR]

A 3-year survey on sulfate-reducing bacteria ( SRB) was conducted in the waters of the arsenic-rich acid mine drainage ( AMD) located at Carnoulès ( France) to determine the influence of environmental parameters on their community structure. The source ( S5 station) exhibited most extreme conditions with p H lowering to ~1.2; iron, sulfate, and arsenic concentrations reaching 6843, 29 593, and 638 mg L−1, respectively. The conditions were less extreme at the downstream stations S1 (p H ~3.7; iron, sulfate, and arsenic concentrations of 1114, 4207, and 167 mg L−1, respectively) and COWG (p H ~3.4; iron, sulfate, and arsenic concentrations of 854, 3134, and 110 mg L−1, respectively). SRB community structures were characterized by terminal restriction fragment length polymorphism and library analyses based on dsrAB genes. The predominant dsrAB sequences detected were most similar to the family Desulfobulbaceae. Additionally, certain phylotypes could be related to spatio-temporal fluctuations of p H, iron, and arsenic species. For example, Desulfohalobiaceae-related sequences were detected at the most acidic sample (p H 1.4) with high iron and arsenic concentrations (6379 and 524 mg L−1, respectively). New dsrAB sequences, with no isolated representatives, were found exclusively in COWG. This study gives new insights on SRB community dynamics in AMD systems. [ABSTRACT FROM AUTHOR]

This study intended to unravel the physiological interplay in an anaerobic microbial community that degrades toluene under sulfate-reducing conditions combining proteomic and genetic techniques. An enriched toluene-degrading community (Zz5-7) growing in batch cultures was investigated by DNA- and protein-based analyses. The affiliation and diversity of the community were analysed using 16S ribosomal RNA (rRNA) genes as a phylogenetic marker as well as bssA and dsrAB genes as functional markers. Metaproteome analysis was carried out by a global protein extraction and a subsequent protein separation by two-dimensional gel electrophoresis (2-DE). About 85% of the proteins in the spots were identified by nano-liquid chromatography coupled with electrospray mass spectrometry (nano-LC-ESI-MS/MS) analysis. DNA sequencing of bssA and the most abundant dsrAB amplicons revealed high similarities to a member of the Desulfobulbaceae, which was also predominant according to 16S rRNA gene amplicons. Metaproteome analysis provided 202 unambiguous protein identifications derived from 236 unique protein spots. The proteins involved in anaerobic toluene activation, dissimilatory sulfate reduction, hydrogen production/consumption and autotrophic carbon fixation were mainly affiliated to members of the Desulfobulbaceae and several other Deltaproteobacteria. Phylogenetic and metaproteomic analyses revealed a member of the Desulfobulbaceae as the key player of anaerobic toluene degradation in a sulfate-reducing consortium. This is the first study that combines genetic and proteomic analyses to indicate the interactions in an anaerobic toluene-degrading microbial consortium. [ABSTRACT FROM AUTHOR]

The impact of legacy nuclear waste on the compositional diversity and distribution of sulfate-reducing bacteria in a heavily contaminated subsurface aquifer was examined. dsrAB clone libraries were constructed and restriction fragment length polymorphism (RFLP) analysis used to evaluate genetic variation between sampling wells. Principal component analysis identified nickel, nitrate, technetium, and organic carbon as the primary variables contributing to well-to-well geochemical variability, although comparative sequence analysis showed the sulfate-reducing bacteria community structure to be consistent throughout contaminated and uncontaminated regions of the aquifer. Only 3% of recovered dsrAB gene sequences showed apparent membership to the Deltaproteobacteria. The remainder of recovered sequences may represent novel, deep-branching lineages that, to our knowledge, do not presently contain any cultivated members; although corresponding phylotypes have recently been reported from several different marine ecosystems. These findings imply resiliency and adaptability of sulfate-reducing bacteria to extremes in environmental conditions, although the possibility for horizontal transfer of dsrAB is also discussed. [ABSTRACT FROM AUTHOR]