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.