TRANSFORMABLE MUTANTS OF A BIOPESTICIDE STRAIN STREPTOMYCES-GRISEOVIRIDIS K61

The aim of this work was to isolate transformable mutants of Streptomy ces griseoviridis K61 without affecting the secondary metabolism of th is strain. S. griseoviridis K61 produces an antifungal aromatic heptae ne polyene antibiotic, and is used as a biological control agent. In p rotoplast transformation experiments using plasmid pIJ702 DNA, the few spontaneous transformants were phenotypically bald and their secondar y metabolism was pleiotropically affected. By mutagenizing K61 with N- methyl-N'-nitro-N-nitrosoguanidine (MNNG) a highly transformable varia nt K61-42 was obtained. Protoplasts of S. griseoviridis K61-42 could b e transformed by several model plasmids producing 10(4)-10(5) transfor mants/mug plasmid DNA. The polyene synthesis of K61-42 was normal, mak ing this strain a useful tool in genetic studies on the mechanism of b iopesticide action.