Antimicrobial Activities of Sponge-Derived Microorganisms from Coastal Waters of Central Vietnam

Bacteria associated with invertebrates are considered as good sources for biologically active compounds. Sponge-derived bacteria were screened for antimicrobial activities, the presence of the cluster genes of polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs), and through a colony picking method. Crude extracts of broth cultures were tested for microbial inhibition. Eleven out of 25 isolated strains showed inhibition of at least one of eight tested indicator microorganisms. Antimicrobial activities were observed in the strains coded HM5, HM6, and HM9 with the presence of NRPS and PKSII genes, whereas the isolate HM21 held both NRPS and PKSII and inhibited only the growth of Bacillus subtilis by the well diffusion method and only inhibited Serratia marcescens by the colony picking method. Two isolates, HM5 and HM6, belonged to the species of Bacillus. Interestingly, the isolate HM9 was nearest to Streptomyces mexicanusT NBRC100915 (GenBank accession number AB249966) with 94% sequence similarity. This potent strain HM9 could possibly be considered as a new species and a good source for bioactive compound discovery. Some isolates showed NRPS/PKS genes but did not exhibit antimicrobial activity. Thus, we suggested that both molecular and traditional methods should be conducted for the screening of antimicrobial producers.