Synthetic community producing bacterial inhibitory proteins to control postharvest black spot disease of winter jujube.

Postharvest fungal decay, particularly black spot disease caused by Alternaria alternata, poses a significant challenge to the storage and economic value of winter jujube (Ziziphus jujuba Mill. cv. Dongzao). While synthetic communities have emerged as a promising sustainable alternative to chemical fungicides, the specific metabolites driving their biocontrol efficacy remain poorly understood. This study aimed to identify and characterize the primary antifungal components produced by a specialized synthetic community. After systematically excluding the interference of organic acids and hydrogen peroxide, proteinaceous substances in the cell-free supernatant were identified as the dominant inhibitory agents. In vitro assays demonstrated that crude protein extracts from the cell-free supernatant from the synthetic community achieved 100% inhibition against A. alternata mycelial growth. Furthermore, in vivo experiments revealed that these proteins effectively suppressed black spot development by inducing systemic resistance in winter jujube fruits. Using LC-MS/MS analysis, we identified several key functional proteins, including subtilisin (EC 3.4.21.62), lytic enzyme L27, alkaline protease P6, and bacillopeptidase F (EC 3.4.21.-). These findings elucidate the biochemical basis of synthetic community-mediated pathogen suppression and provide a robust molecular foundation for developing novel protein-based bio-preservatives for post-harvest fruit protection.