Biocontrol of Aspergillus flavus on peanut kernels by use of a strain of marine Bacillus megaterium

A strain of marine Bacillus megaterium isolated from the Yellow Sea of East China was evaluated for its activity in reducing postharvest decay of peanut kernels caused by Aspergillus flavus in in vitro and in vivo tests. The results showed that the concentrations of antagonist had a significant effect on biocontrol effectiveness in vivo: when the concentration of the washed bacteria cell suspension was used at 1 × 109 CFU/ml, the percentage rate of rot of peanut kernels was 31.67% ± 2.89%, which was markedly lower than that treated with water (the control) after 7 days of incubation at 28 °C. The results also showed that unwashed cell culture of B. megaterium was as effective as the washed cell suspension, and better biocontrol was obtained when longer incubation time of B. megaterium was applied. When the incubation time of B. megaterium was 60-h, the rate of decay declined to 41.67% ± 2.89%. Furthermore, relative to the expression of 18S rRNA, the mRNA abundances of aflR gene and aflS gene in the experiment group were 0.28 ± 0.03 and 0.024 ± 0.005 respectively, indicating that this strain of B. megaterium could significantly reduce the biosynthesis of aflatoxins and expression of aflR gene and aflS gene (p < 0.01). To the best of our knowledge, this is a first report demonstrating that the marine bacterium B. megaterium could be used as a biocontrol agent against postharvest fungal disease caused by A. flavus.