A new kind of fertility variant in Streptomyces coelicolor.

class of fertility variants, called “ultra-fertile” (UF) , has been identified A in the actinomycete Streptomyces coelicolor A3 ( 2 ) (HOPWOOD, HAROLD, VIVIAN and FERGUSON 1968); these variants differ strikingly in their sexual capabilities from the strains that had previously been encountered in S. coielicolor genetics (HOPWOOD 1967). It seems likely that UF variants will contribute to an understanding of the normal process of genetic transfer in this organism, about which litde is yet known, just as the well-known fertility variants (Hfr and F-) of the original Ff strain of Escherichia coli K-12 led to the elucidation of the sexual process in that bacterium. The present paper describes the isolation of UF strains and some of the characteristics of genetic recombination in crosses involving them.