DEGRADATION OF METHYL-BROMIDE BY METHANOTROPHIC BACTERIA IN CELL-SUSPENSIONS AND SOILS

Cell suspensions of Methylococcus capsulatus mineralized methyl bromid e (MeBr), as evidenced by its removal from the gas phase, the quantita tive recovery bf Br- in the spent medium, and the production of (CO2)- C-14, from [C-14]MeBr. Methyl fluoride (MeF) inhibited oxidation of me thane as well as that of [C-14]MeBr. The rate of MeBr consumption by c ells varied inversely with the supply of methane, which suggested a co mpetitive relationship between these two substrates. However, MeBr did not support growth of the methanotroph. In soils exposed to high leve ls (10,000 ppm) of MeBr, methane oxidation,vas completely inhibited. A t this concentration, MeBr removal rates were equivalent in killed and live controls, which indicated a chemical rather than biological remo val reaction. At lower concentrations (1,000 ppm) of MeBr, methanotrop hs were active and MeBr consumption rates were 10-fold higher in live controls than in killed controls. Soils exposed to trace levels (10 pp m) of MeBr demonstrated complete consumption within 5 h of incubation, while controls inhibited with MeF or incubated without O-2 had 50% lo wer removal rates. Aerobic soils oxidized [C-14]MeBr to (CO2)-C-14, an d MeF inhibited oxidation by 72%. Field experiments demonstrated sligh tly lower MeBr removal rates in chambers containing MeF than in chambe rs lacking MeF. Collectively, these results show that soil methanotrop hic bacteria, as well as other microbes, can degrade MeBr present in t he environment.