Characterization of two subsurface H-2-utilizing bacteria, Desulfomicrobium hypogeium sp nov and Acetobacterium psammolithicum sp nov., and their ecological roles

We examined the relative roles of acetogenic and sulfate-reducing bacteria in H-2 consumption in a previously characterized subsurface sandstone ecosy stem, Enrichment cultures originally inoculated with ground sandstone mater ial obtained from a Cretaceous formation in central New Mexico were grown w ith hydrogen in a mineral medium supplemented with 0.02% yeast extract. Sul fate reduction and acetogenesis occurred in these cultures, and the two mos t abundant, organisms carrying out the reactions were isolated. Based on 16 S rRNA analysis data and on substrate utilization patterns, these organisms were named Desulfomicrobium hypogeium sp, nov. and Acetobacterium psammoli thicum sp, nov. The steady-state H-2 concentrations measured in sandstone-s ediment slurries: (threshold concentration, 5 nM), in pure cultures of sulf ate reducers (threshold concentration, 2 nM), and in pure cultures of aceto gens (threshold concentrations 195 to 414 nM) suggest that sulfate reductio n is the dominant terminal electron-accepting process in the ecosystem exam ined. In an experiment in which direct competition for H-2 between D. hypog eium and A. psammolithicum was examined, sulfate reduction was the dominant process.