Molecular Insights into Ammonium Sulfate-Induced Secretome Reprogramming of Bacillus subtilis Czk1 for Enhanced Biocontrol Against Rubber Tree Root Rot

Root rot diseases caused by <i>Ganoderma pseudoferreum</i> and <i>Pyrrhoderma noxium</i> inflict substantial economic losses in rubber tree (<i>Hevea brasiliensis</i>) cultivation, while conventional control methods face environmental and resistance challenges. This study aimed to specifically investigate the molecular mechanisms by which ammonium sulfate enhances the biocontrol efficacy of <i>Bacillus subtilis</i> Czk1. Using label-free quantitative proteomics (LC-MS/MS), we characterized ammonium sulfate-induced alterations in the secretory proteome of Czk1. A total of 351 differentially expressed proteins (DEPs) were identified, with 329 significantly up-regulated and 22 down-regulated. GO functional enrichment analysis indicated that up-regulated DEPs were associated with metabolic pathways (glyoxylate/dicarboxylate, arginine/proline, cofactor biosynthesis) and extracellular localization (13 proteins), while down-regulated DEPs were linked to small molecule catabolism. KEGG pathway annotation identified DEP involvement in 124 pathways, including secondary metabolite biosynthesis and membrane transport. These findings demonstrate that ammonium sulfate remodels the Czk1 secretome to enhance the expression of key antagonistic proteins, thereby providing crucial molecular targets and a scientific foundation for developing effective biofungicides against rubber root rot, with clear practical implications for sustainable disease management.