Candidatus Desulfofervidus auxilii, a hydrogenotrophic sulfate‐reducing bacterium involved in the thermophilic anaerobic oxidation of methane

Abstract

SummaryThe anaerobic oxidation of methane (AOM) is mediated by consortia of anaerobic methane-oxidizing archaea (ANME) and their specific partner bacteria. In thermophilic AOM consortia enriched from Guaymas Basin, members of the ANME-1 clade are associated with bacteria of the HotSeep-1 cluster, which likely perform direct electron exchange via nanowires. The partner bacterium was enriched with hydrogen as sole electron donor and sulfate as electron acceptor. Based on phylogenetic, genomic and metabolic characteristics we propose to name this chemolithoautotrophic sulfate reducer Candidatus Desulfofervidus auxilii. Ca. D. auxilii grows on hydrogen at temperatures between 508C and 708C with an activity optimum at 608C and doubling time of 4-6 days. Its genome draft encodes for canonical sulfate reduction, periplasmic and soluble hydrogenases and autotrophic carbon fixation via the reductive tricarboxylic acid cycle. The presence of genes for pili formation and cytochromes, and their similarity to genes of Geobacter spp., indicate a potential for syntrophic growth via direct interspecies electron transfer when the organism grows in consortia with ANME. This first ANME-free enrichment of an AOM partner bacterium and its characterization opens the perspective for a deeper understanding of syntrophy in anaerobic methane oxidation.

Gene expression and ultrastructure of meso‐ and thermophilic methanotrophic consortia

“…Recent studies provided insights into the draft genome of the AOM partner bacteria HotSeep‐1 (Wegener et al ., ; Krukenberg et al ., ) and Seep‐SRB1 (Skennerton et al ., ). Here we analyzed the draft genome and transcriptome of two Seep‐SRB2 types, representing environmentally relevant partner bacteria from a clade described by Kleindienst and colleagues ().…”

“…The draft genomes of the two types of Seep‐SRB2 bacteria associated with the mesophilic ANME‐2c and ‐1a had a size of 3.6 Mb (E20) and 2.6 Mb (G37), and an estimated completeness of 91%–94% and 91%–95%, respectively (see Table ). This is in the range of what has been reported for HotSeep‐1 (2.5 Mb, 97% completeness; Krukenberg et al ., ) and Seep‐SRB1a (∼ 3 Mb; Skennerton et al ., ). Congruent with our observations from the ANME draft genomes, the GC content of the partner bacteria draft genomes did not show temperature‐dependent variations (47% in E20 Seep‐SRB2, 49% in G37 Seep‐SRB2 and 37% in G60 HotSeep‐1).…”

Harnessing a methane‐fueled, sediment‐free mixed microbial community for utilization of distributed sources of natural gas

“…Previous efforts with sediment‐free ANME‐SRB enrichments have focused largely on the physiological relationships between consortia members (Krukenberg et al, ; Laso‐Pérez et al, ). The resulting mixed cultures can take years to establish and have diminished methane‐dependent sulfate reduction rates (Wegener, Krukenberg, Ruff, Kellermann, & Knittel, ).…”

Reverse Methanogenesis and Respiration in Methanotrophic Archaea

“…This implies that ANME-1 use a different mechanism for DIET and could explain the need for less MHCs by ANME-1 (Table 2) and the observed pili-derived nanowires produced by the bacterial partner [116]. The genome of the bacterial partner of ANME-1 (“HotSeep-1”) encoded 24 c -type cytochromes of which 10 were similar to secreted MHCs of Geobacter sulfurreducens [120] which also uses pili for DIET [121]. …”