Caproicibacter fermentans gen. nov., sp. nov., a new caproate-producing bacterium and emended description of the genus Caproiciproducens

A strictly anaerobic bacterial strain designated EA1(T) was isolated from an enrichment culture inoculated with biogas reactor content. Cells of strain EA1(T) are spore-forming rods (1-3x0.4-0.8 mu m) and stain Gram-negative, albeit they possess a Gram-positive type of cell-wall ultrastructure. Growth of strain EA1(T) was observed at 30 and 37 degrees C and within a pH range of pH 5-9. The major components recovered in the fatty acid fraction were C-14:0, C-16:0, C-16:0 DMA (dimethyl acetal) and C-16:1 omega 7c. Strain EA1(T) fermented several mono- and disaccharides. Metabolic end products from fructose were acetate, butyrate, caproate and lactate. Furthermore, ethanol, CO2 and H-2 were identified as products. The genome consists of a chromosome (3.9 Mbp) with 3797 predicted protein-encoding genes and a G+C content of 51.25 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain EA1(T) represents a novel taxon within the family Oscillospiraceae. The most closely related type strains of EA1(T), based on 16S rRNA gene sequence identity, are Caproiciproducens galactitolivorans BS-1(T) (94.9 %), [Clostridium] leptum DSM 753(T) (93.8 %), [Clostridium] sporosphaeroides DSM 1294(T) (91.7 %) and Ruminococcus bromii ATCC 27255(T) (91.0 %). Further phenotypic characteristics of strain EA1(T) differentiate it from related, validly described bacterial species. Strain EA1(T) represents a novel genus and novel species within the family Oscillospiraceae. The proposed name is Caproicibacter fermentans gen. nov., sp. nov. The type strain is EA1(T) (DSM 107079(T)=JCM 33110(T)).