Evaluation of the Genus Thiothrix Winogradsky 1888 (Approved Lists 1980) Emend. Aruga Et Al. 2002: Reclassification of Thiothrix Disciformis to Thiolinea Disciformis Gen. Nov., Comb. Nov., and of Thiothrix Flexilis to Thiofilum Flexile Gen. Nov.,...

Thiothrix is the type genus of the Thiotrichaceae in the Thiotrichales of the Gammaproteobacteria, comprising nine species of sulfur-oxidising filamentous bacteria, which are variously autotrophic, heterotrophic or have mixed metabolic modes. Within the genus, four species show 16S rRNA gene identities lower the Yarza threshold for the rank of genus (94.5 %) - Thiothrix disciformis, Thiothrix flexilis, Thiothrix defluvii and Thiothrix eikelboomii - as they show no affiliation to extant genera, a polyphasic study was undertaken including biochemical, physiological and genomic properties and phylogeny based on the 16S rRNA gene (rrs), recombination protein A (RecA), polynucleotide nucleotidyltransferase (Pnp), translation initiation factor IF-2 (InfB), glyceraldehyde-3-phosphate dehydrogenase (GapA), glutaminyl-tRNA synthetase (GlnS), elongation factor EF-G (FusA) and concatamers of 53 ribosomal proteins encoded by rps, rpl and rpm operons, all of which support the reclassification of these species. We thus propose Thiolinea gen. nov. and Thiofilum gen. nov. for which the type species are Thiolinea disciformis gen. nov., comb. nov. and Thiofilum flexile gen. nov., comb. nov. We also propose that these genera are each circumscribed into novel families Thiolinaceae fam. nov. and Thiofilaceae fam. nov., and that Leucothrix and Cocleimonas are circumscribed into Leucotrichaceaefam. nov. and provide emended descriptions of Thiothrix and Thiotrichaceae.