Genomic and physiological characterization of the Verrucomicrobia isolate Geminisphaera colitermitum gen. nov., sp. nov., reveals microaerophily and nitrogen fixation genes.

Previously we reported the cultivation of novel verrucomicrobia, including strain TAV2 (93% 16S rRNA gene identity to its nearest cultivated representative, Opitutus terreae PB90-1) from the gut of the termite Reticulitermes flavipes. To gain better insight into the Verrucomicrobia as a whole and understand the role of verrucomicrobia within the termite gut ecosystem, we analyzed a draft genome and undertook a physiological characterization of TAV2. Strain TAV2 is an autochthonous member of the R. flavipes gut microbiota and groups phylogenetically among diverse Verrucomicrobia from R. flavipes and other termites that are represented by 16S rRNA gene sequences alone. TAV2 is a microaerophile, possessing a high-affinity cbb(3)-type terminal oxidase-encoding gene and exhibiting an optimum growth rate between 2 and 8% (vol/vol) oxygen. It has the genetic potential to degrade cellulose, an important function within termite guts, but its in vitro substrate utilization spectrum was limited to starch and a few mono- and disaccharides. Growth occurred on nitrogen-free medium, and genomic screening revealed genes for dinitrogenases, heretofore detected in only a few members of the Verrucomicrobia. This represents the first (i) characterization of a verrucomicrobial species from the termite gut, (ii) report of nif and anf genes in a nonacidophilic verrucomicrobial species, and (iii) description of a microaerophilic genotype and phenotype in this phylum of bacteria. The genetic and physiological distinctiveness of TAV2 supports its recognition as the type strain of a new genus and species, for which the name Geminisphaera colitermitum gen. nov., sp. nov., is proposed.