Streptomyces strains isolated from soil were found to possess various numbe
rs of genes from the streptomycin biosynthesis cluster. The strains missing
genes from the cluster also lacked the ability to produce streptomycin. Tw
o of the isolates which contain only part of the cluster are apparently rec
ipients of a gene transfer event. The implications for the role of gene tra
nsfer in antibiotic evolution are discussed.