Construction of a single component producer from the wild type avermectin producer Streptomyces avermitilis.

Most microbial secondary metabolites are producec as complexes of closely related compoundsby theii producing organisms. The avermectins1*, milbemycins2 and nemadectins3~5) are typical examples produced ii such a manner. The milbemyciif complex is known t( consist of more than twenty components6 ~ 8), however only a few are commercial products. A rationale for thii phenomenon may be related to the complexity of thei biosyntheses and/or lower degrees of substrate speci ficities of the biosynthetic enzymes. The avermectin