Selection of mutant methanotrophic bacteria capable of efficiently degrading halogenated hydrocarbons typically found in numerous wastewater sources is described. The mutants are distinguishable from parental strains in having a unique resistance to the presence of copper while exhibiting unusually high degradation rates toward trichlorethylene. Methylosinus trichosporium A.T.C.C. 55314 strains are particularly good sources of the described mutants which may be obtained using a new method of selection and screening. The disclosed microorganisms may be immobilized on various matrices and are particularly adaptable for use in bioreactors. Further, the methanotrophic bacteria have antibiotic resistance to streptomycin or rifampicin B.