Evolution of Secondary Metabolite Genes in Three Closely Related Marine Actinomycete Species
ABSTRACTThe marine actinomycete genusSalinisporais composed of three closely related species. These bacteria are a rich source of secondary metabolites, which are produced in species-specific patterns. This study examines the distribution and phylogenetic relationships of genes involved in the biosynthesis of secondary metabolites in the salinosporamide and staurosporine classes, which have been reported forS. tropicaandS. arenicola, respectively. The focus is on “Salinispora pacifica,” the most recently discovered and phylogenetically diverse member of the genus. Of 61S. pacificastrains examined, 15 tested positive for a ketosynthase (KS) domain linked to the biosynthesis of salinosporamide K, a new compound in the salinosporamide series. Compound production was confirmed in two strains, and the domain phylogeny supports vertical inheritance from a common ancestor shared withS. tropica, which produces related compounds in the salinosporamide series. There was no evidence for interspecies recombination amongsalAKS sequences, providing further support for the geographic isolation of these two salinosporamide-producing lineages. In addition, staurosporine production is reported for the first time forS. pacifica, with 24 of 61 strains testing positive forstaD, a key gene involved in the biosynthesis of this compound. High levels of recombination were observed betweenstaDalleles inS. pacificaand the cooccurring yet more distantly relatedS. arenicola, which produces a similar series of staurosporines. The distributions and phylogenies of the biosynthetic genes examined provide insight into the complex processes driving the evolution of secondary metabolism among closely related bacterial species.