Strain improvement of Arthrobacter simplex by protoplast fusion

An L-tryptophan auxotroph and milky mutants were derived from an inducible cholesterol oxidase-producing bacterium, Arthrobacter simplex USA18, via UV-mutagenesis. Protoplasts of these mutants and a constitutive cholesterol oxidase producer, strain US3011, were prepared by growing cells in the presence of ampicillin (20 mu g ml(-1)) followed by digestion with lysozyme, Protoplast fusion between tested strains with complementary characteristics was achieved in the presence of 20-40% polyethylene glycol 6000, The fusion frequency was about 1.5-1.7 x 10(-3). The cholesterol oxidase activity of four fusants in a cholesterol-containing medium was 20-60% higher than that of parental strains. This study demonstrated that protoplast fusion is applicable to strain improvement of Arthrobacter strains for enzyme production.