Methanol Promotes Atmospheric Methane Oxidation by Methanotrophic Cultures and Soils

Two methanotrophic bacteria, Methylobacter albus BG8 and Methylosinus trichosporium OB3b, oxidized atmospheric methane during batch growth on methanol. Methane consumption was rapidly and substantially diminished (95% over 9 days) when washed cell suspensions were incubated without methanol in the presence of atmospheric methane (1.7 ppm). Methanotrophic activity was stimulated after methanol (10 mM) but not methane (1,000 ppm) addition. M. albus BG8 grown in continuous culture for 80 days with methanol retained the ability to oxidize atmospheric methane and oxidized methane in a chemostat air supply. Methane oxidation during growth on methanol was not affected by methane deprivation. Differences in the kinetics of methane uptake (apparent K_m and V_max) were observed between batch- and chemostat-grown cultures. The V_max and apparent K_m values (means ± standard errors) for methanol-limited chemostat cultures were 133 ± 46 nmol of methane 10⁸ cells⁻¹ h⁻¹ and 916 ± 235 ppm of methane (1.2 μM), respectively. These values were significantly lower than those determined with batch-grown cultures (V_max of 648 ± 195 nmol of methane 10⁸ cells⁻¹ h⁻¹ and apparent K_m of 5,025 ± 1,234 ppm of methane [6.3 μM]). Methane consumption by soils was stimulated by the addition of methanol. These results suggest that methanol or other nonmethane substrates may promote atmospheric methane oxidation in situ.