Screening bacterial symbionts of marine invertebrates for ribosomally synthesized natural products
Pharmaceutical research and development strategies rely on the constant discovery of novel natural products as potential drugs. Recent studies have shown that the microorganisms associated with sponges are the true producers of some previously isolated compounds. This study created a large collection of bacterial symbionts associated with the South African marine sponge, Hamacantha esperioides. The bioactivity assays performed, showed that 44 isolates produced compounds with antimicrobial or anti-inflammatory activity. The successful identification of novel species that produce potential natural products highlights the importance of cultivation-dependent methods. To further screen for natural products, a cultivation-independent approach was used. A sequenced-based method, based on the biosynthetic genes of polytheonamide, was developed to screen for proteusins in sponge metagenomic DNA and the genomes of bacterial symbionts. The degenerate primers could amplify the targeted genes from DNA known to contain homologues. Evaluation of the primers' specificity showed non-specific amplification of genes, some containing similar conserved domains as the target genes. This study demonstrated that the use and development of cultivation-dependent and -independent screens are important for the discovery of novel natural products from the symbiotic bacteria of South African sponges.