ANTIFUNGAL ACTION AND METABOLIC PROFILING OF SEED ENDOPHYTIC BACILLUS CEREUS STRAIN JCM 2152 AGAINST TOXIGENIC ASPERGILLUS SPECIES FROM MAIZE

Abstract

Contamination of maize grains with aflatoxigenic genus Aspergillus negatively impacts public health, food security, and postharvest storage. Biological control (BC) of molds is becoming more popular. Regardless, invitro validation of BC agents’ efficiency is crucial to successful postharvest deployment.  This study investigated antifungal action of an endophytic Bacillus cereus against four Aspergillus strains, and its metabolic profiling. Decontaminated apple seeds and maize grains were blended, and plated on mannitol egg yolk polymyxin B agar, and potato dextrose agar for Bacillus and Aspergillus strains isolation respectively. Molecular identification of isolates was done. A 72 h Bacillus cell-free extract dilutions (undiluted, 1:10, and 1:1000), were used in agar well antifungal susceptibility test against three Aspergillus species, and aflatoxigenic A. flavus ATCC 22546. Nystatin was positive control, and incubation done at 28 °C. AST was repeated at pH 6, 8 and 9, and zones of inhibition were measured (mm). Minimum inhiibitiory concentration and minimum fungicidal concentration was done. Enzyme assay and GCMS scan of CFE, and ZOI agar blocks were done for A. flavus ATCC 22546 and an A. flavus.  B. cereus strain JCM 2152, and A. flavus isolate K₁, A. flavus isolate W₅ and A. fumigatus strain 3162953 were confirmed. The 1:10 dilution produced widest ZOI, and A. flavus isolate W₅ susceptibility was significant at 30.00 ± 2.50 mm. Also, pH and ZOI correlated.  MIC ranged 1:8 – 1:256, and was fungistatic. Hexadecanoic acid, 4-methyl-3-pent-2-one, and extracellular enzymes were detected. A. flavus isolate W₅ was significantly susceptible to enzymes. Possible synergistic inhibition was the mechanism of inhibition, and preliminary features required of a BC for postharvest trial were affirmed for B. cereus strain JCM 2152.