Construction and phenotypes of double sporulation deficient mutants in Streptomyces coelicolor A3(2).

In whiA, B, G and H mutants of Streptomyces coelicolor A3(2), aerial hyphae develop but sporulation speta are not formed. Septa are produced by whiI mutants but are spaced abnormally far apart. Mutants in each locus have a distinctive aerial mycelium morphology, except for whiA and B mutants which are closely similar. Seven strains were made with pairwise combinations of whiA and B mutations with whiG, H and I mutations and with each other. The genotypes of these strains were confirmed by suitable crosses and their aerial mycelium morphology examined. An indirect procedure was used to determine the aerial mycelium morphology of whiGH, GI and HI double mutants. The double mutants always closely resembled one of the single mutant parent strains in morphology and a consistent scheme of epistasis was obtained--whiG being epistatic to whiH, A, B and I; whiH to whiA, B and I; and whiA or B to whiI. These results point to the absence of any complex interactions between gene products, which might have been revealed by the occurrence of novel phenotypes in double mutants or by inconsistencies in the epistasis scheme.