Screening, production, and characterization of biologically active secondary metabolite(s) from marine Streptomyces sp. PA9 for antimicrobial, antioxidant, and mosquito larvicidal activity

1319-1326Bioprospecting of actinobacteria from understudied ecosystems is a promising source for extracting novel bioactive metabolites. A study was undertaken to characterize and analyze the bio-efficacy of actinobacterial extract for antimicrobial, larvicidal, and antioxidant activities. Seven morphologically different actinobacterial cultures isolated from mangrove rhizosphere sediment near Parangipettai, South India, were tested for antimicrobial activity. Bioactive metabolites from one potential strain PA9 were produced by submerged fermentation. The selected Streptomyces sp. PA9 was subjected to the production of crude extract for antimicrobial, larvicidal, and antioxidant activity. The actinobacterial compound was characterized by Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography–mass spectrometry (GC–MS). The PA9 actinobacterial crude extract showed best antimicrobial activity against clinical bacteria, Salmonella typhi (21.6 ± 0.88 mm) and fungi, Candida albicans (26.6 ± 0.88 mm). The PA9 extract showed significant larvicidal activity against Culex quinquefasciatus with LC50=173.21 µg/ml and r2=0.841. The PA9 extract also exhibited antioxidant activity from DPPH (72%) and nitric oxide free radicals (85%). The characterization of the PA9 extract by FTIR analysis showed the presence of possible functional groups. Active compounds were isolated by HPLC and GC–MS with major and minor peaks observed on the basis of retention time. The bio-efficacy of PA9 has warranted further studies to develop a baseline for the drug development