Syntrophic relationship between sulfate reducers and methanogens isolated from paddy field soil
1999
Kubota, A. (Hirosaki Univ., Aomori (Japan)) | Takeda, K.
The number of sulfate reducers and methanogens in paddy field soils was enumerated by the role tube and most probable number methods, respectively, and then sulfate reducers and methanogens were isolated from the enrichment cultures. The syntrophic relationship between the sulfate reducers and methanogens was examined. 1) Both bacterial numbers were 10(5) g(-1) dry soil in paddy field soil. No significant difference in the number of both bacteria was detected between fertilizer treatment conditions. 2) A sulfate reducer, strain SK3-4, was motile, Gram-negative and had vibrio-shaped cells. Acetate and sulfide were the only end products detected during growth with lactate in the presence of sulfate. 3) A H2-utilizing methanogen, strain MK3-6, had rod-shaped cells. H2 and formate were the only electron donors utilized for methanogenesis. An acetate-utilizing methanogen, strain MSK3-1, had coccoid cells. Most of the cells grew as aggregates. The strain was able to use acetate, H2+CO2, methanol and methylamines as substrates for methanogenesis. 4) Strain SK3-4 was able to grow in a sulfate-free medium when it was cultured in association with strain MK3-6 and strain MSK3-1. Sulfate reducers seem to be involved in methanogenesis as hydrogen-producing acetogenic bacteria in syntrophic association with hydrogen-utilizing methanogens under sulfate-free conditions. 5) When paddy field soils were incubated anaerobically with the addition of lactate, the lactate was completely degraded to CH4 and CO2. The bacterial number of sulfate reducers stayed at the 10(5) level. The sulfate reducers seem to oxidize lactate to acetate in syntrophic association with methanogens. When sulfate and lactate were added to the soils, lactate was oxidized to acetate and methanogenesis was inhibited
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