Gram-positive spore-forming sulfate reducers and particularly members of the genus Desulfotomaculum are commonly found in the subsurface biosphere by culture based and molecular approaches. Due to their metabolic versatility and their ability to persist as endospores. Desulfotomaculum spp. are well-adapted for colonizing environments through a slow sedimentation process. Because of their ability to grow autotrophically (H2/CO2) and produce sulfide or acetate, these microorganisms may play key roles in deep lithoautotrophic microbial communities. Available data about Desulfotomaculum spp. and related species from studies carried out from deep freshwater lakes, marine sediments, oligotrophic and organic rich deep geological settings are discussed in this review.

Summary Around the world, several dozen deep sedimentary aquifers are being used for storage of natural gas. Ad hoc studies of the microbial ecology of some of them have suggested that sulfate reducing and methanogenic microorganisms play a key role in how these aquifers' communities function. Here, we investigate the influence of gas storage on these two metabolic groups by using high‐throughput sequencing and show the importance of sulfate‐reducing Desulfotomaculum and a new monophyletic methanogenic group. Aquifer microbial diversity was significantly related to the geological level. The distance to the stored natural gas affects the ratio of sulfate‐reducing Firmicutes to deltaproteobacteria. In only one aquifer, the methanogenic archaea dominate the sulfate‐reducers. This aquifer was used to store town gas (containing at least 50% H2) around 50 years ago. The observed decrease of sulfates in this aquifer could be related to stimulation of subsurface sulfate‐reducers. These results suggest that the composition of the microbial communities is impacted by decades old transient gas storage activity. The tremendous stability of these gas‐impacted deep subsurface microbial ecosystems suggests that in situ biotic methanation projects in geological reservoirs may be sustainable over time.

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