Predominant Acidilobus-Like Populations from Geothermal Environments in Yellowstone National Park Exhibit Similar Metabolic Potential in Different Hypoxic Microbial Communities
ABSTRACTHigh-temperature (>70°C) ecosystems in Yellowstone National Park (YNP) provide an unparalleled opportunity to study chemotrophic archaea and their role in microbial community structure and function under highly constrained geochemical conditions.Acidilobusspp. (orderDesulfurococcales) comprise one of the dominant phylotypes in hypoxic geothermal sulfur sediment and Fe(III)-oxide environments along with members of theThermoprotealesandSulfolobales. Consequently, the primary goals of the current study were to analyze and compare replicatede novosequence assemblies ofAcidilobus-like populations from four different mildly acidic (pH 3.3 to 6.1) high-temperature (72°C to 82°C) environments and to identify metabolic pathways and/or protein-encoding genes that provide a detailed foundation of the potential functional role of these populationsin situ. De novoassemblies of the highly similarAcidilobus-like populations (>99% 16S rRNA gene identity) represent near-complete consensus genomes based on an inventory of single-copy genes, deduced metabolic potential, and assembly statistics generated across sites. Functional analysis of coding sequences and confirmation of gene transcription byAcidilobus-like populations provide evidence that they are primarily chemoorganoheterotrophs, generating acetyl coenzyme A (acetyl-CoA) via the degradation of carbohydrates, lipids, and proteins, and auxotrophic with respect to several external vitamins, cofactors, and metabolites. No obvious pathways or protein-encoding genes responsible for the dissimilatory reduction of sulfur were identified. The presence of a formate dehydrogenase (Fdh) and other protein-encoding genes involved in mixed-acid fermentation supports the hypothesis thatAcidilobusspp. function as degraders of complex organic constituents in high-temperature, mildly acidic, hypoxic geothermal systems.