Hydrogen as a substrate for methanogenesis and sulphate reduction in anaerobic saltmarsh sediment

Hydrogen gas stimulated sulphate reduction in a saltmarsh sediment and the importance of H2 transferred from organotrophic bacteria to the sulphate-reducers is discussed. beta-fluorolactate inhibited sulphate reduction whether lactate, ethanol or hydrogen was being used as growth substrate. When added to sediment beta-fluorolactate inhibited sulphate reduction with a consequent increase in methane production. Addition of H2 stimulated methanogenesis in sediment and this stimulation was greater if CO2 was also present. Hydrogen availability was the primary limitation of methanogenesis but the low concentration of dissolved CO2 in seawater may limit methane production even if H2 is available. The removal of inhibition of methanogenesis by the use of fluorolactate to suppress sulphate reduction or by the provision of hydrogen indicates competitive inhibition of methanogens by sulphate reducers utilizing transferred hydrogen.