Antimicrobial Activities of Ophiobolins from Bipolaris maydis against Foodborne Pathogenic Bacteria via Biofilm Formation Inhibition

Bipolarizens A-O (1-15), 15 previously undescribed ophiobolin derivatives, and one known analog, 3-anhydroophiobolin A (16), were discovered from the fungus Bipolaris maydis. All of the compounds were elucidated by extensive spectroscopic data, DP4+ analyses, electronic circular dichroism (ECD) calculations, and X-ray crystallography studies. Compound 1 had a 15-oxatetracyclo[9.3.2.0²,¹².0⁴,⁸]hexadecane-bridged system. Compound 2 featured a 5/8/5/7-tetracyclic sesterterpenoid framework, constituting only the second reported example of this structural class. Bioactivity research revealed that compound 16 exhibited moderate antimicrobial activity against Bacillus cereus, with a MIC of 50 μg/mL. Further crystal-violet assay, fluorescent staining, and scanning electron microscopy significantly demonstrated that compound 16 could inhibit biofilm formation and cellular morphological integrity of B. cereus. These findings not only enrich the structural diversity of ophiobolins but also offer a promising molecular scaffold to control foodborne contamination associated with B. cereus and its biofilm.