| Summary: | The Philippine archipelago is geographically positioned in the tropics with rich areas of marine biodiversity. Its marine sediments harbor actinomycetes that exhibit antibacterial activity. Screening of actinomycetes isolated from marine sediments collected near the coast of Islas de Gigantes, Iloilo showed one isolate that exhibited high activity against the multidrug-resistant <i>Staphylococcus aureus</i> (MRSA) strain carrying the Staphylococcal Cassette Chromosome <i>mec</i> (SCC<i>mec</i>) type 1 gene, a biomarker for drug resistance. The isolate was identified as <i>Streptomyces sp</i>. strain DSD011 based on its 16s rRNA and protein-coding genes (<i>atpD, recA, rpoB</i>, and <i>trpB</i>) sequences, and was found to be a new species of salt-tolerant marine <i>Streptomyces</i>. Further, the strain harbors both non-ribosomal peptide synthetase (NRPS) and type II polyketide synthase (PKS) in its genome. The targeted chromatographic isolation and chemical investigations by Liquid Chromatography Mass Spectrometry-Time of Flight (LCMS-TOF), tandem mass spectrometry (MS/MS), and Global Natural Product Social molecular networking (GNPS) of the antibiotics produced by the strain, afforded the two polycyclic aromatic polyketide angucycline glycosides, fridamycin A (<b>1)</b> and fridamycin D (<b>2</b>), which are products of type II PKS biosynthesis. Compounds <b>1</b> and <b>2</b> displayed antibacterial activity against MRSA with minimum inhibitory concentration(MIC) of 500 μg/mL and 62.5 μg/mL, respectively. These results suggest that the underexplored marine sediments near the coast of Islas de Gigantes, Iloilo offer access to undiscovered <i>Streptomyces</i> species that are invaluable sources of antibiotic leads.
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