<i>Bacillus aerophilus</i> A5 suppresses tobacco root rot and gene expressions involved in fungal chitin metabolism

To investigate the fungal response to A5, <i>F. solani</i> was exposed to 10% sterile A5 fermentation supernatant and analyzed using transcriptomic sequencing. GO and KEGG enrichment analyses showed differentially expressed genes (DEGs) involved in UDP-<i>N</i>-acetylglucosamine biosynthesis and associated cell wall precursor metabolic processes. Because <i>F. oxysporum</i> has a more established genetic manipulation system in tobacco root rot research, this species was used for downstream functional validation.

RT-qPCR confirmed the significant expression responses of FOXG_19023, FOXG_10443, and FOXG_12345 after the treatment with A5 supernatant. Subsequent construction of knockout mutants demonstrated that deletion of FOXG_19023 significantly restricted colony growth, suggesting that FOXG_19023 may contribute to vegetative growth of <i>F. oxysporum</i>, although its specific role in UDP-<i>N</i>-acetylglucosamine-related cell wall metabolism remains to be explored.

Overall, A5 was identified as a tobacco root rot biocontrol bacterium with activity against <i>Fusarium</i> pathogens. These results further suggest that A5 may affect expression of genes involved in pathogen UDP-<i>N</i>-acetylglucosamine-related metabolism, and this response may be associated with impaired <i>Fusarium</i> hyphal growth. This study provides a potential biocontrol resource for sustainable tobacco root rot management and offers candidate pathogen-side targets for future studies on the molecular mechanisms underlying <i>Bacillus</i>-mediated suppression of <i>Fusarium</i>.</p>