Genome-Driven Discovery of Anti-MDR Bacterial Heptapeptides from a Cold-Seep-Derived Bacillus Strain

With the increasing emergence of multidrug-resistant (MDR) bacteria, there is an urgent need to discover new antibiotics. In this study, genome mining coupled with anti-bacterial assay guided the targeted isolation of two new heptapeptides nobilamide Q3 (<b>1</b>) and R3 (<b>2</b>). These compounds were identified as new stereoisomers of the known scaffold A-3302-B (<b>3</b>). The structures of these compounds were elucidated through a combination of MS, NMR spectroscopy and Marfey's analysis. Anti-MDR bacterial assays showed that compounds <b>2</b> and <b>3</b> exhibited effective growth inhibition against the Gram-positive MDR bacterial strain <i>Staphylococcus aureus</i> CCARM 3090 with MIC values of 3.25-6.5 μg/mL. Notably, our study reveals stereochemistry-dependent differences in their antibacterial activities, providing new insights into the structure-activity relationship of this class of peptides. Finally, an analysis of the biosynthetic gene cluster responsible for their production was conducted. This study underscores the significance of exploring cold-seep environments as a reservoir for discovering new antibiotics and provides a structural starting point for the future optimization of antimicrobial peptides.