Bacillus amyloliquefaciens PP19 regulation of microbial communities and suppression of Peronophythora litchii.

BACKGROUND: Litchi downy blight (LDB) is a major disease affecting litchi (Litchi chinensis), damaging fruits, inflorescences, and leaves, and significantly hindering the development of the litchi industry in China and globally. Bacillus amyloliquefaciens PP19 has demonstrated significant biocontrol efficacy against LDB, but its mechanism of action remains unclear. RESULTS: This study used microbiome analysis and bacterial interaction studies to investigate the biocontrol mechanism by which PP19 regulates core microbial communities on litchi exocarps to suppress LDB. First, 16S rRNA diversity analysis revealed that PP19 pretreatment effectively prevented bacterial diversity imbalances caused by Peronophythora litchii infection, maintaining microbial stability by regulating the abundance of specific genera (Actinomycetospora, Paenibacillus, and Spirosoma). Microbial interaction networks and functional prediction revealed that PP19 might modulate bacterial motility pathways, resulting in changes to the abundance of specific microbial communities on litchi exocarps. These changes facilitated the formation of a core microbiome negatively correlated with the abundance of P. litchii. By isolating and genetically identifying 83 cultivable bacterial strains from litchi exocarps and using correlation analysis, 16 candidate strains with potentially significant interactions with PP19 and P. litchii SC18 were identified. Plate antagonism, liquid co-culture, and leaf biocontrol efficacy analyses ultimately identified four representative strains (Sphingomonas sp. F14, Rhizobium sp. F26, Pseudomonas sp. F32, and Enterobacter cloacae F63) with significant interactions with either PP19 or P. litchii. Interaction, motility, and biofilm production analyses showed that PP19 interacted with the four litchi exocarp bacteria to prevent disease through various mechanisms, and enhanced their motility and biofilm production to varying degrees. CONCLUSIONS: PP19 regulates core microbial communities on litchi exocarps, maintaining community stability and enriching interacting strains which together inhibit the growth of P. litchii, thereby achieving biocontrol efficacy. Video Abstract.