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., comb nov., with emended description of Thiothrix.

Thiothrix is the type genus of the Thiotrichaceae in the Thiotrichales of the 21 Gammaproteobacteria, comprising nine species of sulfur-oxidising filamentous Bacteria, 22 which are variously autotrophic, heterotrophic or have mixed metabolic modes. Within the 23 genus, 4 species show 16S rRNA gene identities lower the Yarza threshold for the rank of 24 genus (94.5 %) – Thiothrix disciformis, Thiothrix flexilis, Thiothrix defluvii and Thiothrix 25 eikelboomii – as they show no affiliation to extant genera, a polyphasic study was undertaken 26 including biochemical, physiological and genomic properties and phylogeny based on the 27 16S rRNA gene (rrs), recombination protein A (RecA), polynucleotide nucleotidyltransferase 28 (Pnp), translation initiation factor IF-2 (InfB), glyceraldehyde-3-phosphate dehydrogenase 29 (GapA), glutaminyl-tRNA synthetase (GlnS), elongation factor EF-G (FusA) and 30 concatamers of 53 ribosomal proteins encoded by rps, rpl and rpm operons, all of which 31 support the reclassification of these species. We thus propose Thiolinea gen. nov. and 32 Thiofilum gen. nov. for which the type species are Thiolinea disciformis gen. nov., comb. 33 nov. and Thiofilum flexile gen. nov., comb. nov. We also propose that these genera are each 34 circumscribed into novel families Thiolinaceae fam. nov. and Thiofilaceae fam. nov., and 35 that Leucothrix and Cocleimonas are circumscribed into Leucotrichaceae fam. nov. and 36 provide emended descriptions of Thiothrix and Thiotrichaceae.