[Isolation of actinobacteria with antibiotic associated with soft coral Nephthea sp]

The present study aims to isolate and identify actinobacteria associated with the soft coral Nephthea sp., and to isolate natural products from these actinobacteria under the guidance of PCR screening for polyketides synthase (PKS) genes.

Eleven selective media were used to isolate actinobacteria associated with the soft coral Nephthea sp. collected from Yongxin Island. The isolated actinobacteria were classified on the basis of phylogenetic tree analysis of their 16S rRNA genes. Degenerated primers targeted on conserved KS (ketoacyl-synthase) domain of type I PKS genes were used to screen for potential isolates. The positive isolates were cultured in three different media to check their producing profiles. One bioactive strain that is rich in metabolites was subjected to larger scale fermentation for isolating bioactive natural products.

A total of 20 strains were isolated from Nephthea sp., and were categorized into 3 genera including Streptomyces, Dietzia and Salinospora, among which 18 strains were positive in screening with type I PKS genes. Two bioactive compounds rifamycin S and rifamycin W were isolated and identified from Salinospora arenicola SH04.

This is the first report of isolating indigenous marine actinobacteria Salinospora from the soft coral Nephthea sp. It provides an example of isolating bioactive secondary metabolites from cultivable actinobacteria associated with Nephthea sp. by PCR screening.