Volatile organic compounds produced by Bacillus aryabhattai AYG1023 against Penicillium expansum causing blue mold on the Huangguan pear

Previous research on Bacillus aryabhattai has mainly focused on bioremediation, biosynthesis, and promotion of plant growth, whereas the function of B. aryabhattai on antifungal activity remains to be explored. In this study, we isolated a biocontrol bacterium with antagonistic activity against post-harvest pathogenic fungi by releasing volatile organic compounds (VOCs). We aimed to assess the effectiveness of VOCs produced by B. aryabhattai in prevention of the development of blue mold caused by Penicillium expansum in the Huangguan pear, and reveal the inhibitory mechanism against the pathogenic fungi. Using molecular methods, the biocontrol bacterium was identified as Bacillus aryabhattai AYG1023. 2-Nonanol was identified as the main VOC by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC/MS). It showed strong inhibition of mycelial growth and conidial germination when treated at the minimum inhibitory concentration (MIC). Scanning and transmission electron microscopy showed that 2-nonanol caused abnormal changes in mycelial and conidial ultrastructure. 2-Nonanol also damaged the integrity of fungal cell membranes and reduced the ergosterol content to 44.77% of P. expansum. In addition, the production of secondary metabolites in P. expansum including patulin and citrinin was significantly reduced by 2-nonanol. Transcriptome analysis revealed that 2-nonanol modulated the expression of genes involved in development, and conidiation pathways, as well as secondary metabolite biosynthesis including steroid biosynthesis, citrinin production and patulin production. Furthermore, blue mold was completely inhibited by treatment with 0.04 mu L mL-1 2-nonanol for 48 h on the Huangguan pear. In conclusion, Bacillus aryabhattai AYG1023 was identified as a promising and efficient agent for controlling postharvest diseases via the release of VOCs, and the outcome of this study lays a theoretical foundation for future applications.