Effective utilization of dichloromethane by a newly isolated strain Methylobacterium rhodesianum H13.

An effective dichloromethane (DCM) utilizer Methylobacterium rhodesianum H13 was isolated from activated sludge. A response surface methodology was conducted, and the optimal conditions were found to be 4.5 g/L Na2HPO4·12H2O, 0.5 g/L (NH4)2SO4, an initial pH of 7.55, and a temperature of 33.7 °C. The specific growth rate of 0.25 h(-1) on 10 mM DCM was achieved, demonstrating that M. rhodesianum H13 was superior to the other microorganisms in previous investigations of DCM utilization. DCM mineralization paralleled the production of cells, CO2, and water-soluble metabolites, as well as the release of Cl(-), whereas the carbon distribution and Cl(-) yield varied with DCM concentrations. The facts that complete degradation only occurred with DCM concentrations below 15 mM and repetitive degradation of 5 mM DCM could proceed for only three cycles were ascribed to pH decrease (from 7.55 to 3.02) though a buffer system was employed.

[Isolation and degradation characteristics of dichloromethane-degradation bacterial strain by Methylobacterium rhodesianum H13].

A dichloromethane-degrading bacterium Methylobacterium rhodesianum H13 which utilized the DCM as the sole carbon and energy source was isolated. According to the research, M. rhodesianum H13 could completely degrade 5 mmol x L(-1) DCM in 23 h with the initial cell concentration of 0.82 mg x L(-1), pH 7.0, 30 degrees C, and the cell yield rate was about 0.136 g x g(-1) DCM. With the degradation of DCM, Cl- concentration gradually raised (the release of Cl- concentration was about 2 times higher as the DCM), pH value dropped to 6.75, and the solution was weakly acidic. Temperature, pH, DCM concentration, Cl- concentration and other factors were investigated through the shake flask experiments, and the optimal conditions for DCM degradation were: temperature 30 degrees C, pH 7.0. The study also indicated that 5 mmol x L(-1) of DCM was the optimum concentration for M. rhodesianum H13 and high levels of DCM could inhibit the degradation. The research has an important application value for the DCM environmental pollution.