Caldifarcimen microaerophilum gen. nov., sp. nov., a facultatively anaerobic, thermophilic bacterium of a novel bacterial phylum, Caldifarciminota phyl. nov., formerly called candidate phylum WOR-3, description of Caldifarciminaceae fam. nov., Caldifarciminales ord. nov. and Caldifarciminia classis nov.

A facultatively anaerobic, thermophilic, Gram-negative bacterium, strain sy37 T , isolated from a deep-sea hydrothermal field and belonging to the candidate phylum WOR-3, was characterized in detail. The cells were non-motile long rods with pili and grew via respiration with 2–10% (v/v) oxygen and elemental sulphur as electron acceptors. Optimum growth was observed at 75 °C, pH 6.0 and 3.5% (w/v) NaCl with a doubling time of 10 h. iso-C 17 : 0 was found to be the major fatty acid and menaquinone-8 was identified as the major respiratory quinone. The G+C content of the genomic DNA was 60.6 mol%. Based on the results of phylogenetic analyses of the 16S rRNA gene and genome sequences, together with the phenotypic characterization of strain sy37 T , we propose the name Caldifarcimen microaerophilum gen. nov., sp. nov. for strain sy37 T (=NBRC 116057 T =BCRC 81450 T ). In addition, we propose the associated family, order, class and phylum as Caldifarciminaceae fam. nov., Caldifarciminales ord. nov., Caldifarciminia classis nov. and Caldifarciminota phyl. nov., respectively, in the bacterial kingdom Pseudomonadati .