Syntrophomonas erecta subsp. sporosyntropha subsp. nov., a spore-forming bacterium that degrades short chain fatty acids in co-culture with methanogens

Two obligate anaerobic bacterial strains (5-3-ZT and Y4-1) were isolated from river sediment and rice field mud, respectively. They degraded straight-chain fatty acids with 4–8 carbon atoms in syntrophic association with methanogens, however, neither tested branch-chain fatty acids nor could benzoate be degraded. The strains formed spores when cocultured with methanogens on butyrate, or when grew on butyrate plus dimethyl sulfoxide (DMSO) in pure culture. The cells were slightly curved rods with Gram-negative cell wall structure, and contained small amount of poly β-hydroxyalkanoate. The strains could not degrade butyrate alone, nor could use fumarate, sulfate, thiosulfate, sulfur or nitrate as electron acceptors except DMSO for butyrate degradation. The generation time of strain 5-3-ZT was about 12 h when growing on crotonate at 37 °C. The growth of the new strains occurred in the range of pH 5.5–8.4, and of temperature 20–48 °C, and at NaCl concentration of 0–700 mM. The G+C content of the genomic DNA of strain 5-3-ZT was 40.6 mol%. Phylogenetic analysis based on 16S rRNA gene similarity showed the two strains to be a member of species Syntrophomonas erecta (98.4–98.9% sequence similarity), however they differed from the existing strains in both phenotypic and genetic characteristics. Therefore, a new subspecies of S. erecta, S. erecta subsp. sporosyntropha was proposed. The type strain was 5-3-ZT (=CGMCC1.5032T=JCM13344T).