Reclassification of Thiomicrospira hydrogeniphila (Watsuji et al. 2016) to Thiomicrorhabdus hydrogenophila comb. nov., with emended description of Thiomicrorhabdus (Boden et al., 2017)

The genus Thiomicrorhabdus (Tmr) in the Piskirickettsiaceae in the Thiotrichales of the Gammaproteobacteria contains four species of sulfur-oxidising obligate chemolithoautotroph with validly published names, all previously classified as Thiomicrospira (Tms) species. Here we demonstrate that Thiomicrospira hydrogeniphila, a recently published hydrogen-utilising chemolithoautotroph closely related to Thiomicrorhabdus frisia (type species of Thiomicrorhabdus) should be classified as a member of the genus Thiomicrorhabdus and not Thiomicrospira, as Thiomicrorhabdus hydrogeniphila comb. nov., on the basis of comparative physiology and morphology as well as 16S rRNA (rrs) gene identity of Tms. hydrogeniphila MAS2^T being closer to that of Tmr. frisia JB-A2^T (99.1 %) than to Tms. pelophila DSM 1534^T (90.5 %) or Hydrogenovibrio marinus MH-110^T (94.1 %), and on the basis of the topology of 16S rRNA gene maximum likelihood trees, which clearly place Tms. hydrogeniphila within the genus Thiomicrorhabdus. It was also noted that thiosulfate-grown Thiomicrorhabdus spp. can be distinguished from Thiomicrospira spp. or Hydrogenovibrio spp. on the basis of the 3 dominant fatty acids (C_{16: 1}, C_{18: 1} and C_{16: 0}), and from other Thiomicrorhabdus spp. on the basis of the fourth dominant fatty acid, which varies between the species of this genus – which could provide a useful diagnostic method. We provide an emended description of Thiomicrorhabdus (Boden R, Scott KM, Williams J, Russel S, Antonen K et al. Int J Syst Evol Microbiol 2017;67:1140–1151) to take into account the properties of Thiomicrorhabdus hydrogeniphila comb. nov.