Bacillus species are extensively studied, utilized, and commercialized biocontrol agents, demonstrating significant effectiveness in managing a variety of plant diseases. Bacillus possesses a robust intrinsic biosynthetic ability, capable of producing a diverse array of antimicrobial metabolites, including dipicolinic acid (DPA; 2,6-pyridinedicarboxylic acid), which exhibits antifungal properties and serves as a principal structural component of Bacillus spores. This study revealed that DPA exhibits significant antibacterial activity against the hazardous soybean pathogen Xanthomonas citri pv. glycines (Xcg), with an EC50 value of 53.2 μg/mL. DPA inhibited Xcg swimming motility, extracellular protease activity, and biofilm formation, while inducing significant membrane irregularities in Xcg cells. DPA treatment downregulated the expression of several Xcg membrane integrity-related genes, including cirA, czcA, czcB, emrE, and tolC. The preventive and curative application of 500 μg/mL DPA reduced Xcg symptoms by 82.7% and 83.8%, respectively, and induced the accumulation of the isoflavone genistin in soybean leaves. DPA exhibited only weak toxicity in the zebrafish model, suggesting its potential suitability for agricultural commercialization. Overall, this study provides the first detailed characterization of the antibacterial mechanism of DPA against a phytopathogenic bacterium, Xcg, and identifies DPA as a previously underexplored antibacterial metabolite from Bacillus and Paecilomyces with potential for disease management.
Chen et al. (Sun,) studied this question.