Antimicrobial effect of Bacillus licheniformis HN-5 bacitracin A on rice pathogen Pantoea ananatis

Pantoea ananatis is a plant pathogenic bacterium that severely impacts rice. In spite of its worldwide prevalence, limited studies have been conducted so far on the control of P. ananatis . Bacitracin A is a non-ribosomal peptide antibiotic with strong antibacterial activity produced by Bacillus licheniformis strain HN-5. We investigated the mechanisms of action underlying the biocontrol and bactericidal efficacy of bacitracin A against P. ananatis . Fluorescence microscopy and bacterial cell viability analyses revealed that the median effective concentration of bacitracin A against P. ananatis was 9.10 μg ml −1 . Scanning and transmission electron microscopy showed that bacitracin A damaged the cell wall and membrane of P. ananatis . Quantitative real-time PCR indicated that the transcriptional expression of ftsZ , glmS , and gumD , which are involved in cell division, cell-wall biosynthesis, and extracellular polymeric substance biosynthesis, respectively, was upregulated at 12 h and significantly downregulated at 24 h after bacitracin A treatment in P. ananatis . Bacitracin A caused cell leakage and changes to membrane permeability in P. ananatis , supporting its use as a natural biocontrol agent for P. ananatis .