Degradation of trichloroethene by a linear-plasmid-encoded alkene monooxygenase in Rhodococcus corallinus (Nocardia corallina) B-276

Rhodococcus corallinus (formerly Nocardia corallina) B-276, isolated with p ropene as sale carbon and energy source, is able to oxidize trichloroethene (TCE). Glucose- or propene-grown R. corallinus B-276 cells exhibited no di fference in TCE degradation efficiency. TCE degradation was found to be gro wth-phase-dependent and maximum rates were monitored with stationary-phase cells. K-m and V-max values for TCE degradation of R. corallinus B-276 grow n in nutrient broth medium in the presence of glucose were 187 mu M and 2.4 nmol min(-1) (mg protein)(-1), exhibited the ability to degrade TCE. This result provides clear evidence that the alkene monooxygenase of R. corallin us B-276 catalyses TCE oxidation. R. corallinus B-276 was shown to contain four linear plasmids, pNC10 (70 kb), pNC20 (85 kb), pNC30 (185 kb) and pNC4 0 (235 kb). The observation that pNC30-deficient strains had lost the abili ty to grow on propene suggested that the genes of the propene degradation p athway are encoded by the linear plasmid pNC30. Southern blot analysis with cloned alkene monooxygenase genes from R. corallinus B-276 revealed a posi tive hybridization signal with the linear plasmid pNC30. This result clearl y shows that the alkene monooxygenase is encoded by the linear plasmid pNC3 0. Eleven short-chain-alkene-oxidizing strains were screened for the presen ce of linear plasmids. Among these, four propene-oxidizing Rhodococcus stra ins and one ethene-oxidizing Mycobacterium strain were found to contain lin ear megaplasmids. Southern blot analysis with the alkene monooxygenase reve aled positive signals with linear plasmids of two propene-oxidizing Rhodoco ccus ruber strains. These results indicate that homologous alkene monooxyge nases are encoded by linear plasmids in R. ruber strains.