The Streptomyces coelicolor A3(2) bldB region contains at least two genes involved in morphological development

Streptomyces coelicolor A3(2) bldB mutants are blocked in the formation of aerial hyphae. A phage library of wild-type S. coelicolor DNA was used to isolate recombinant phages which restore wild-type morphological development to several bldB mutants. Of several mutations, one, bld-28, previously mapped at bldB was not complemented by the cloned region, indicating that the bldB locus is composed of at least two distinct genes. Partial localization of bldB-complementing activity showed that a 1.5 kb fragment is sufficient for complementation of the bld-15 mutation whereas bld-17 requires the same region as well as additional sequences. Under stringent conditions, genomic DNA hybridizing to the cloned sequences was absent from other Streptomyces species, including the closely related Streptomyces lividans 66. DNA sequences causing marked plasmid structural instability in S. coelicolor, but not in S. lividans, are also located in this region.