Bacillus sp. Z26 suppresses Alternaria alternata and its mycotoxins by targeting AaPex13-mediated peroxisome biogenesis.

Alternaria alternata is a destructive postharvest pathogen that causes fruit decay and produces multiple mycotoxins, including alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TeA), posing a serious threat to crop quality and food safety. Biocontrol stands out as a promising strategy to mitigate both fungal infection and mycotoxin production. This study investigated that Bacillus sp. Z26 effectively inhibits the mycelial growth and mycotoxin accumulation of A. alternata. Comparative transcriptomic analysis revealed that strain Z26 did not directly repress canonical mycotoxin biosynthetic gene clusters; instead, it caused extensive transcriptional reprogramming in amino acid and lipid metabolism, with peroxisome-associated pathways being prominently affected. Among the downregulated genes, AaPex13 was identified as a key peroxisome biogenesis factor potentially involved in the biocontrol process. Targeted deletion of AaPex13 significantly impaired vegetative growth, conidiation, stress tolerance, and pathogenicity of A. alternata. Notably, loss of AaPex13 almost abolished TeA biosynthesis, while only partially reducing AOH and AME accumulation, indicating distinct metabolic dependencies among these toxins. In parallel, Bacillus sp. Z26 directly and selectively degraded AOH and AME, but not TeA. In grape berry assays, strain Z26 reduced disease severity, lowered mycotoxin contamination, and induced host defense responses, as evidenced by enhanced PPO and PAL activities and increased trans-resveratrol accumulation. Collectively, these findings suggest that Bacillus sp. Z26 suppresses A. alternata through a multifaceted mechanism involving disruption of AaPex13-mediated peroxisome biogenesis, selective detoxification of AOH and AME, and activation of host resistance. This study highlights peroxisome biogenesis as a previously underappreciated vulnerability in A. alternata and provides a potential target for precision biocontrol of Alternaria-associated postharvest diseases and mycotoxin contamination.