Syntrophobacter sulfatireducens sp. nov., a novel syntrophic, propionate-oxidizing bacterium isolated from UASB reactors

Abstract

Two obligate anaerobes, TB8106T and WZH410, which degraded propionate in syntrophic association with methanogens, were isolated from two upflow anaerobic sludge blanket reactors, one treating brewery wastewater and the other bean curd wastewater. The strains were Gram-negative, non-spore-forming and non-motile. Cells were egg-shaped, with a size of 1·0–1·3×1·8–2·2 μm. Growth was observed at 20–48 °C and pH 6·2–8·8. Both strains converted propionate to acetate and methane in co-culture with methanogens, and grew on propionate plus sulfate in pure culture, with a doubling time of 52–55 h at 37 °C. Sulfate and thiosulfate both served as electron acceptors for propionate degradation. The DNA G+C contents of the two strains were 58·5 and 58·7 mol%, respectively. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the strains were closely related to a propionate-oxidizing syntrophic bacterium, Syntrophobacter fumaroxidans DSM 10017T (94·7 % similarity). However, the novel strains could not ferment fumarate, and grew at a more alkaline pH range than Syntrophobacter fumaroxidans. Moreover, the novel isolates had obviously higher growth rates on propionate plus sulfate (0·12 day−1) than Syntrophobacter fumaroxidans DSM 10017T (0·024 day−1). Therefore, a novel species, Syntrophobacter sulfatireducens sp. nov., is proposed, with strain TB8106T (=AS 1.5016T=DSM 16706T) as the type strain.