Members of the metabolically diverse order Nitrosomonadales inhabit a wide range of environments. Two strains affiliated with this order were isolated from soils in Germany and characterized by a polyphasic approach. Cells of strains 0125_3T and Swamp67T are Gram-negative rods, non-motile, non-spore-forming, non-capsulated and divide by binary fission. They tested catalase-negative, but positive for cytochrome c-oxidase. Both strains form small white colonies on agar plates and grow aerobically and chemoorganotrophically on SSE/HD 1 : 10 medium, preferably utilizing organic acids and proteinaceous substrates. Strains 0125_3T and Swamp67T are mesophilic and grow optimally without NaCl addition at slightly alkaline conditions. Major fatty acids are C16 : 1 ω7c, C16 : 0 and C14 : 0. The major polar lipids are diphosphatidylglycerol, phosphatidylethanolamine and phosphatidyglycerol. The predominant respiratory quinone is Q-8. The G+C content for 0125_3T and Swamp67T was 67 and 66.1 %, respectively. The 16S rRNA gene analysis indicated that the closest relatives (<91 % sequence similarity) of strain 0125_3T were Nitrosospira multiformis ATCC 25196T, Methyloversatilis universalis FAM5T and Denitratisoma oestradiolicum AcBE2-1T, while Nitrosospira multiformis ATCC 25196T, Nitrosospira tenuis Nv1T and Nitrosospira lacus APG3T were closest to strain Swamp67T. The two novel strains shared 97.4 % 16S rRNA gene sequence similarity with one another and show low average nucleotide identity of their genomes (83.8 %). Based on the phenotypic, chemotaxonomic, genomic and phylogenetic analysis, we propose the two novel species Usitatibacter rugosus sp. nov (type strain 0125_3T=DSM 104443T=LMG 29998T=CECT 9241T) and Usitatibacter palustris sp. nov. (type strain Swamp67T=DSM 104440T=LMG 29997T=CECT 9242T) of the novel genus Usitatibacter gen. nov., within the novel family Usitatibacteraceae fam. nov.
Keywords: Usitatibacter; soil bacteria.