Geomesophilobacter sediminis gen. nov., sp. nov., Geomonas propionica sp. nov. and Geomonas anaerohicana sp. nov., three novel members in the family Geobacterecace isolated from river sediment and paddy soil

Bacteria in the family Geobacteraceae have been proven to fill important niches in a diversity of anaerobic environments and global biogeochemical processes. Here, three bacterial strains in this family, designated Red875ᵀ, Red259ᵀ, and Red421ᵀ were isolated from river sediment and paddy soils in Japan. All of them are Gram-staining-negative, strictly anaerobic, motile, flagellum-harboring cells that form red colonies on agar plates and are capable of utilizing Fe(III)-NTA, Fe(III) citrate, ferrihydrite, MnO₂, fumarate, and nitrate as electron acceptors with acetate, propionate, pyruvate, and glucose as electron donors. Phylogenetic analysis based on the 16S rRNA gene and 92 concatenated core proteins sequences revealed that strains Red259ᵀ and Red421ᵀ clustered with the type strains of Geomonas species, whereas strain Red875ᵀ formed an independent lineage within the family Geobacteraceae. Genome comparison based on  average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values clearly distinguished these three strains from other Geobacteraceae members, with lower values than the thresholds for species delineation. Moreover, strain Red875ᵀ also shared low average amino acid identity (AAI) and percentage of conserved proteins (POCP) values with the type species of the family Geobacteraceae. Based on these physiological, chemotaxonomic, and phylogenetic distinctions, we propose that strain Red875ᵀ (=NBRC 114290ᵀ = MCCC 1K04407ᵀ) represents a novel genus in the family Geobacteraceae, namely, Geomesophilobacter sediminis gen. nov., sp. nov., and strains Red259ᵀ (=NBRC 114288ᵀ = MCCC 1K05016ᵀ) and Red421ᵀ (=NBRC 114289ᵀ = MCCC 1K06216ᵀ) represent two novel independent species in the genus Geomonas, namely, Geomonas propionica sp. nov. and Geomonas anaerohicana sp. nov., respectively.