Characteristics of an Anaerobic, Syntrophic, Butyrate-degrading Bacterium in Paddy Field Soil

The number of syntrophic butyrate-degrading bacteria in a flooded paddy field soil was 1.7 x 10(3) MPN/g dry soil. Butyrate was degraded to acetate and methane when paddy soils were incubated anaerobically with the addition of butyrate. However, butyrate degradation was completely suppressed by the addition of the specific inhibitor of methanogenesis, 2-bromoethanesulfonate (BES) to the soil. A hydrogen-using methanogen, strain TM-8, was isolated from flooded paddy field soil. Strain TM-8 was identified as Methanobacterium formicicum based on its physiology and phylogeny. Syntrophic butyrate-degrading bacteria were enumerated and isolated using strain TM-8. A syntrophic butyrate-degrading bacterium, strain TB-6, was isolated in coculture with strain TM-8 from paddy soil. The strain was Gram-negative, had curved rods, and grew on crotonate. Sulfate was not used as an electron acceptor. Strain TB-6 was closely related to S. wolfei subsp. wolfei. The relation between strain TB-6 and the members of Syntrophomonas are discussed.