Antimicrobial Activities of Ophiobolins from <i>Bipolaris maydis</i> against Foodborne Pathogenic Bacteria via Biofilm Formation Inhibition

Bipolarizens A-O (<b>1</b>-<b>15</b>), 15 previously undescribed ophiobolin derivatives, and one known analog, 3-anhydroophiobolin A (<b>16</b>), were discovered from the fungus <i>Bipolaris maydis</i>. All of the compounds were elucidated by extensive spectroscopic data, DP4+ analyses, electronic circular dichroism (ECD) calculations, and X-ray crystallography studies. Compound <b>1</b> had a 15-oxatetracyclo[9.3.2.0^2,12.0^4,8]hexadecane-bridged system. Compound <b>2</b> featured a 5/8/5/7-tetracyclic sesterterpenoid framework, constituting only the second reported example of this structural class. Bioactivity research revealed that compound <b>16</b> exhibited moderate antimicrobial activity against <i>Bacillus cereus</i>, with a MIC of 50 μg/mL. Further crystal-violet assay, fluorescent staining, and scanning electron microscopy significantly demonstrated that compound <b>16</b> could inhibit biofilm formation and cellular morphological integrity of <i>B. cereus</i>. These findings not only enrich the structural diversity of ophiobolins but also offer a promising molecular scaffold to control foodborne contamination associated with <i>B. cereus</i> and its biofilm.