Hydrogenobacter thermophilus (strain TK-6) is an obligately chemolithoautotrophic, extremely (and strictly) thermophilic hydrogen-oxidizing bacterium whose optimal growth temperature is around 70 to 75°C and was isolated from hot springs. Phylogenetic analysis based on the 16S ribosomal DNA sequence showed that the strain has the deepest branching point among the Bacteria.

In February 2010, Hydrogenobacter thermophilus strain TK-6 had its genome sequenced and was found to have 1,743,135 base pairs containing 1,963 genes.