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.