Stimulation of Methanogenesis by Slurries of Saltmarsh Sediment after the Addition of Molybdate to Inhibit Sulphate-reducing Bacteria

The addition of 20 mm-molybdate to sediment slurry in order to inhibit sulphate-reducing bacteria increased the amount of methane formed. Only a small proportion (7.8%) of the total methane came from the H2 + CO2 pathway, while methanogenesis from acetate was negligible. Conversion of-14C-labelled formaldehyde, methanol and methionine to 14CH4 by sediment slurry in the presence of molybdate showed that these were potential precursors of the additional methane, although lack of adequate analytical techniques precluded establishment of the quantitative significance of this turnover; [14C]formate was not converted to 14CH4. It is suggested that inhibition of sulphate-reducing bacteria by molybdate immediately increased methanogenesis from formaldehyde, methanol and methionine, and to some extent from H2 + CO2. There was also evidence for longer term development of an increased methanogenic bacterial population when there was no competition from the sulphate-reducing bacteria for available nutrients.