Mcroorgarisms composing synlrophic melhanoseric communly in paddy fieidsoil

本研究的目的是通过培养方法和分子生态学技术对稻田土壤中组成合养产甲烷群落的微生物进行特征分析。在接种于稻田土壤中的丙酸和醋酸盐上富集产甲烷培养物，并对培养物中的微生物群落进行了检测。用变性梯度凝胶电泳法从丙酸培养物中扩增出一条与变形杆菌乙酰化基因密切相关的DNA片段。丙酸杆菌单独不降解丙酸也不产生甲烷，但当丙酸氧化合养培养中的细菌共存时，它会刺激丙酸的降解和产甲烷。结果表明，稻田土壤中可能存在类似的合养作用。醋酸盐培养中以产甲烷古生菌和产甲烷细菌为主。产甲烷产氢细菌，甲烷杆菌属。AH1和硫酸盐还原菌Desulfovibrio sp.A1，是从增菌培养中分离的。菌株AH1和A1共培养降解丙酮酸、乳酸和乙醇为甲烷，表明水稻田土壤中产甲烷菌和硫酸盐还原菌共营养联合产甲烷。然而，共培养并不能将乙酸盐降解为甲烷，也不能证明乙酸盐的合养氧化作用。

The objective of the present research project was to characterize microorganisms composing syntrophic methanogenic community in paddy field soil by the cultivation method and molecular ecological techniques. Methanogenic cultures were enriched on propionate and acetate inoculated with paddy field soil and the microbial communities in the cultures were examined. A DNA fragment closely related to Proteiniphilum acetatigenes was obtained from the culture on propionate by the denaturing gradient gel electrophoresis method. P. acetatigenes alone does not degrade propionate nor produce methane, but stimulates degradation of propionate and methanogenesis when the bacterium coexists in the propionate oxidizing syntrophic culture. The results suggested that similar syntrophic interaction may have functioned in the paddy field soil. Methanosarcina- or Methanobacterium-like methanogenic archaea and a bacterium were predominated in the culture on acetate. A hydrogenotrophic methanogenic strain, Methanobacterium sp. AH1, and a sulfate reducer, Desulfovibrio sp. Al, were isolated from the enrichment culture. Co-culture of strains AH1 and A1 degraded pyruvate, lactate and ethanol to methane, indicating syntrophic association of hydrogenotrophic methanogens and sulfate reducers for methanogenesis in paddy field soil. However, the co-culture did not degrade acetate to methane and syntrophic acetate oxidation could not be demonstrated