The Tol-Pal System Promotes Pseudoiodinine Production by Enhancing Bacterial Growth in Pseudomonas mosselii

Pseudoiodinine is an antimicrobial compound produced by Pseudomonas mosselii that exhibits strong inhibitory activity against bacterial and fungal pathogens of rice, highlighting its potential as a green biopesticide. However, the regulatory mechanisms underlying pseudoiodinine production remain poorly understood. In this study, genome-wide random mutagenesis identified two insertion mutants of 277-3 and 277-23 that completely abolished antagonistic activity against Xanthomonas oryzae pv. oryzicola (Xoc) RS105, with transposon insertions mapped to tolB and tolR, respectively. Further analysis showed that mutations in tolB and tolR significantly impaired bacterial growth during the exponential phase, suggesting that the Tol-Pal system is required for the optimal growth of P. mosselii. Consistently, overexpression of the tol-pal operon resulted in a 3.2-fold increase in pseudoiodinine production compared with the original strain. These findings indicate that the Tol-Pal system contributes to pseudoiodinine production primarily by maintaining efficient bacterial growth. Collectively, this study provides the first insight into the Tol-Pal system in promoting pseudoiodinine production and suggests its potential application in engineering P. mosselii strains.