Inhibition of methanogenesis by methyl fluoride: Studies of pure and defined mixed cultures of anaerobic bacteria and archaea

Abstract

Methyl fluoride (fluoromethane [CH3F]) has been used as a selective inhibitor of CH4 oxidation by aerobic methanotrophic bacteria in studies of CH4 emission from natural systems. In such studies, CH3F also diffuses into the anaerobic zones where CH4 is produced. The effects of CH3F an pure and defined mixed cultures of anaerobic microorganisms were investigated. About 1 kPa of CH3F, similar to the amounts used in inhibition experiments, inhibited growth of and CH4 production by pure cultures of aceticlastic methanogens (Methanosaeta spp. and Methanosarcina spp.) and by a methanogenic mixed culture of anaerobic microorganisms in which acetate was produced as an intermediate. With greater quantities of CH3F, hydrogenotrophic methanogens were also inhibited. At a partial pressure of CH3F of 1 kPa, homoacetogenic, sulfate-reducing, and fermentative bacteria and a methanogenic mixed culture of anaerobic microorganisms based on hydrogen syntrophy were not inhibited. The inhibition by CH3F of the growth and CH4 production of Methanosarcina mazei growing on acetate was reversible. CH3F inhibited only acetate utilization by Methanosarcina barkeri, which is able to use acetate and hydrogen simultaneously, when both acetate and hydrogen were present. These findings suggest that the use of CH3F as a selective inhibitor of aerobic CH4 oxidation in undefined systems must be interpreted with groat care. However, by a careful choice of concentrations, CH3F may be useful for the rapid determination of the role of acetate as a CH4 precursor.