Genomics and the ancient origins of the daptomycin biosynthetic gene cluster.

Daptomycin is a clinically useful lipopeptide antibiotic produced by Streptomyces roseosporus. The antibiotic is assembled by a nonribosomal peptide synthetase (NRPS) mechanism, and the cyclized tridecapeptide contains three non-proteinogenic-amino acids: ornithine (Orn), 3-methyl-glutamic acid (3mGlu) and kynurinine (Kyn). Daptomycin also has three D-amino acids. The two genes that encode proteins involved in the formation of 3mGlu and Kyn have no known orthologs, and hence they are good probes to search for daptomycin-like gene clusters among newly sequenced actinomycete genomes. A recent search with these genes revealed a daptomycin-like gene cluster in Saccharomonospora viridis, a causative agent for farmer's lung disease. S. viridis has a genome of 4.3 Mb, which is about one half the size of Streptomyces genomes. Searches for other NRPS and polyketide synthase (PKS) genes revealed only one other NRPS gene and no PKS genes in S. viridis. The orthologous lipopeptide biosynthetic genes and gene products in S. viridis and S. roseosporus have diverged extensively from a last common ancestor dating back to a pathway that had evolved over 1 billion years ago.