Ralstonia solanacearum Secretions Induce Shifts in Macrolactin Composition and Reduction in Antimicrobial Activity of Bacillus amyloliquefaciens BNC5.

Ralstonia solanacearum, a pathogen causing bacterial wilt, threatens global crop production, necessitating sustainable biocontrol solutions. Bacillus amyloliquefaciens is a promising biocontrol agent, but the mechanisms of its interaction with R. solanacearum are not well understood. This study investigates the effects of R. solanacearum secretions on the growth, metabolite production, and antimicrobial properties of B. amyloliquefaciens BNC5. Untargeted metabolomics revealed increases in two known macrolactins (A and M), six novel macrolactins (BA1-6), and one novel polyketide (BAP1), along with decreases in 7-O-malonyl macrolactin A and a new macrolactin, BA7, following exposure to the secretions. Real-time polymerase chain reaction showed a downregulation of the tailoring enzyme gene bmmGT3. The reduced antimicrobial activity in the exposed extracts (78 vs 39-78 μg mL-1 in unexposed extracts) is likely due to diminished macrolactin efficacy in macrolactin fractions from the exposed (512-1024 μg mL-1) compared to those from the unexposed samples (4 μg mL-1). Supported by tomato pot experiments, these results suggest that applying B. amyloliquefaciens extracts prior to introducing live bacteria may enhance the management of R. solanacearum in severely affected fields, providing a sustainable alternative to chemical pesticides.