Isolation and characterization of a novel Thermodesulfobacterium sp. from laboratory enrichments containing candidate phylum Atribacteria (OP9)

SMSU Event Center BC

Atribacteria (OP9) is candidate phylum with no representatives in pure culture, and is found in various anaerobic environments worldwide. “Caldatribacterium”, a thermophilic lineage within the Atribacteria, is currently being maintained in laboratory enrichment cultures with fucose as a carbon source, where “Caldatribacterium” is present at ~95% relative abundance. Metagenomics and 16S rRNA gene tag sequencing techniques showed that the enrichments growing on fucose appear to be a co-culture of “Caldatribacterium” and an uncultivated member of the genus Thermodesulfobacterium, which consists of sulfate-reducing thermophiles. Due to the failed attempts to isolate “Caldatribacterium” by dilution-to- extinction or plating techniques, it has been hypothesized that there is a syntrophic relationship between the two bacteria. To better understand the potential interaction between these two microbes, several isolates of Thermodesuflobacterium were obtained from the fucose enrichments under sulfate-reducing conditions, and one of these isolates was characterized. Genomic comparison of a metagenome bin corresponding to the dominant Thermodesulfobacterium lineage present in the co-cultures to other sequenced members of the genus Thermodesulfobacterium by in silico DNADNA hybridization showed percentages lower than 70%, suggesting that the Thermodesulfobacterium in the co-cultures represents a distinct species. The isolate’s 16S rRNA gene sequence is 98.7% identical to other related species, also consistent with it representing a novel species. The characterization of Thermodesulfobacterium will help give insight into possible syntrophic interactions between the isolate and “Caldatribacterium”, with Thermodesulfobacterium possibly consuming hydrogen and/or organic acids produced by “Caldatribacterium”, and will also allow for formal proposal for this Thermodesulfobacterium strain as a new species