Selective inhibition of reactions involved in methanogenesis and fatty acid production on rice roots

Abstract

Washed excised roots of rice (Oryza sativa) produced H2, CH4 and fatty acids (millimolar concentrations of acetate, propionate, butyrate; micromolar concentrations of isovalerate, valerate) when incubated under anoxic conditions. Surface sterilization of the root material resulted in the inactivation of the production of CH4, a strong reduction of the production of fatty acids and a transient (75 h) but complete inhibition of the production of H2. Radioactive bicarbonate was incorporated into CH4, acetate, propionate and butyrate. About 20-40% of the fatty acid carbon originated from CO2 reduction. In the presence of phosphate, CH4 was exclusively produced from H2/CO2, since phosphate selectively inhibited acetoclastic methanogenesis. Acetoclastic methanogenesis was also selectively inhibited by methyl fluoride, while chloroform or 2-bromoethane sulfonate inhibited CH4 production completely. Production of CH4, acetate, propionate and butyrate from H2/CO2 was always exergonic with Gibbs free energies