Enhanced Iturin A Synthesis and Antifungal Effect of <i>Bacillus amyloliquefaciens</i> by Genetic Engineering of Protease, ATP Supply and <i>itu</i> Operon

Mold causes significant economic losses and threatens human and animal health. Iturin A is a natural compound with potent antifungal activity, and iturin A-producing bacteria can provide potential biocontrol solution for mold contamination. In this study, the biosynthesis of iturin A was significantly enhanced by deleting nonessential protease genes, enhancing ATP supply, and modifying the <i>itu</i> operon in <i>Bacillus amyloliquefaciens</i>. Accordingly, the efficient iturin A-producing strain <i>B. amyloliquefaciens</i> BAX-bac3 was constructed, and the iturin A yield reached 1.20 g/L, increased by 2.99-fold compared to the wild-type strain HZ-12. <i>In vitro</i> agar plate assays showed that the increased iturin A synthesis significantly enhanced the antifungal activity of BAX-bac3 against <i>Penicillium chrysogenum</i> and <i>Penicillium expansum</i>, two common pathogenic fungi. Additionally, biocontrol experiments conducted on tobacco leaves and apples further confirmed that BAX-bac3 treatment effectively prevented fungal infection. In conclusion, this study presents a novel and effective strategy to enhance iturin A synthesis for development of biocontrol agents.