Investigation of biotechnological potential of sponge‐associated bacteria collected in Brazilian coast

Marine bacteria are a rich source of structurally unique natural compounds, several of which have shown a wide variety of biological activities. In this study, the metabolites present in the culture supernatants of the eight sponge-associated bacteria were extracted using ethyl acetate, and all extracts showed activity against Staphylococcus aureus. Subsequently, the extracts of the Pseudomonas fluorescens H40 and H41, and Pseudomonas aeruginosa H51 were subjected to solvent partitioning, and the active fractions were submitted to chromatographic separation. Three different active fractions were obtained, one of which was identified as diketopiperazine cyclo-(L-Leu-L-Pro). This substance was bactericidal for Staph. aureus and Ps. aeruginosa and showed cytotoxic activity against HEp-2 tumour cells. Putative gene fragments coding for the type I polyketide synthase (PKS-I) and nonribosomal peptide synthetase (NRPS) domains were PCR-amplified from five and three strains, respectively. The results suggest that sponge-associated bacteria analysed in this study may represent a potential source for production of antimicrobial substances against bacterial pathogens of medical importance. Significance and Impact of the Study This study presents the first report of the isolation of diketopiperazine cyclo-(L-Leu-L-Pro) produced by Pseudomonas fluorescens strains associated with marine sponges and describes the detection of the PKS and NRPS genes in strains of Ps. fluorescens, Pseudomonas aeruginosa and Pseudovibrio denitrificans associated with sponges. The combination of PKS/NRPS gene-based molecular approaches and culture-dependent methods demonstrated that sponge-associated bacteria can contribute to the search for new sources of antimicrobial substances. This is an important strategy for developing alternative therapies to treat infections caused by pathogenic bacteria.