Reclassification of Thiobacillus aquaesulis (Wood & Kelly, 1995) as Annwoodia aquaesulis gen. nov., comb. nov., transfer of Thiobacillus (Beijerinck, 1904) from the Hydrogenophilales to the Nitrosomonadales, proposal of Hydrogenophilalia class. nov. within the ‘Proteobacteria’, and four new families within the orders Nitrosomonadales and Rhodocyclales

The genus Thiobacillus comprises 4 species with validly published names, of which T. 17 aquaesulis DSM 4255T (= ATCC 43788T) is the only species that can grow heterotrophically 18 or mixotrophically – the rest being obligate autotrophs - and has a significant metabolic 19 difference in not producing tetrathionate during the oxidation of thiosulfate during 20 autotrophic growth. On the basis of this and differential chemotaxonomic properties and a 21 16S rRNA gene identity of 93.4% to the type species Thiobacillus thioparus DSM 505T, we 22 propose that it is moved to a novel genus Annwoodia gen. nov., for which the type species is 23 Annwoodia aquaesulis gen. nov., comb. nov. We confirm the position of the genus 24 Thiobacillus in the Betaproteobacteria falls within the Nitrosomonadales rather than the 25 Hydrogenophilales as previously proposed. Within the Nitrosomonadales we propose the 26 circumscription of genera to form the Thiobacilliaceae fam. nov. and the Sterolibacteriaceae 27 fam. nov. We propose the merging of the family Methylophilaceae into the 28 Nitrosomonadales, and that the Sulfuricellaceae be merged into the Gallionellaceae, leaving 29 the orders Methylophilales and Sulfuricellales defunct. In the Rhodocyclales we propose the 30 Azonexaceae fam. nov. and the Zoogloeaceae fam. nov. We also reject the 31 Hydrogenophilales from the Betaproteobacteria on the basis of a very low16S rRNA gene 32 identity with the class-proper as well as physiological properties, forming the 33 Hydrogenophilalia class. nov. in the ‘Proteobacteria’. We provide emended descriptions of 34 Thiobacillus, Hydrogenophilales, Hydrogenophilaceae, Nitrosomonadales, Gallionellaceae, 35 Rhodocyclaceae and the Betaproteobacteria.