Identification of Obscurolide-Type Metabolites and Antifungal Metabolites from the Termite-Associated <i>Streptomyces neopeptinius</i> BYF101

Abstract

<i>Streptomyces</i> spp. are well-known symbiotic microorganisms that produce antimicrobial metabolites against various pathogens. We isolated actinomycetes from the body surface of the termite <i>Odontotermes formosanus</i> and identified it as <i>Streptomyces neopeptinius</i> BYF101 based on 16S rRNA phylogenetic analysis. Chemical analysis of the cultures of termite-associated <i>S. neopeptinius</i> BYF101 via HR-MS² and GNPS analyses enabled the isolation and identification of 20 metabolites, including the unreported obscurolide-type metabolites (<b>1</b>-<b>3</b>). The chemical structures of unreported compounds (<b>1</b>-<b>3</b>) were elucidated using HR-ESI-MS and 1D and 2D NMR analysis, and their absolute configurations were determined via chemical reactions followed by the application of competing enantioselective acylation (CEA) and computational methods for ECD and DP4+ probability calculation. The isolated compounds (<b>1</b>-<b>20</b>) were tested to determine their antifungal activity against two human fungal pathogens, <i>Candida albicans</i> and <i>Cryptococcus neoformans.</i> Among the compounds tested, indole-3-carboxylic acid (<b>9</b>) displayed antifungal activity against <i>C. neoformans</i>, with an MIC value of 12 μg/mL.