Heterozygous clones in Streptomyces coelicolor

Abstract

SUMMARY: Certain of the colonies that arise when spores from a mixed culture of two complementary auxotrophic strains of Streptomyces coelicolor A3(2) are plated on a selective medium give rise to a mixture of spores with parental and recombinant genotypes. These heterogeneous colonies (heteroclones) probably develop from spores containing heterozygous nuclei which segregate during the development of the colonies. The heterozygous nuclei probably undergo a number of equational divisions before segregating. The markers in two linkage groups segregate independently. Large imbalances in the allele ratios and in the frequencies of complementary genotypes have been attributed to terminal chromosome deletions which affect both chromosome pairs. Absence (or homozygosity of the markers) of one whole chromosome is observed very often in heteroclones selected on media which make one chromosome dispensable. The heteroclones provide an efficient system for studying the genetics of the organism without recourse to selective methods.