Stereospecificity and physiology of co-oxidative production of chemicals by methanotrophic bacteria. [Methane monooxygenase:a2]

摘要

Methanotrophic bacteria can use methane as a sole source of carbon and energy. The enzyme responsible for the oxidation of methane in these organisms, methane monooxygenase, is also able to biotransform a number of substrates into industrially important chemicals. One such example is the oxidation of propylene to propylene oxide. Several strains of mesophilic and thermophilic methanotrophs have been tested for their ability to produce propylene oxide with formate, methanol, and methane as the co-oxidative substrates. Cultures in the late stationary phase were found to be more productive than exponentially growing cultures. Methane did not inhibit propylene epoxidation on low-density cultures; in fact, the yields of propylene oxide were greater when both methane and propylene were present than when only propylene was present. In higher-density cultures, however, methane did appear to inhibit oxidation of propylene. The effects of several culture parameters such as pH, temperature, and concentration of micronutrients on propylene oxide production ad steroespecificity were determined. Propylene oxide production was proportional to the amount of cell loading up to 14 g/L. Unwashed cells produced more propylene oxide than washed cells. The long- and short-term inhibitory effects of propylene oxide on the methanotrophic strains were also investigated. A tolerance of up to 1 M propylene oxide was observed, and the maximum inhibitory effect was seen within 30 minute. The steroespecificity for propylene oxide production and oxidation of 3-methylcyclohexene was determined for several strains. Methylosinus trichosporium (OB3b), particularly a cell-free extract of this strain, had the greatest steroespecificity. 13 refs., 12 figs., 3 tabs.