Biocontrol activities and mechanisms of endophytic Bacillus licheniformis SY41 against Atractylodes chinensis root rot

• Bacillus licheniformis SY41 was an endophytic bacteria isolated from the root tissues of atractylodes chinensis . • Strain SY41 exhibited a potent inhibitory effect on diverse phytopathogenic fungi. • VOCs from strain SY41 inhibited the growth of pathogenic fungi through multiple mechanisms. • Some DEGs involved in cell wall and cell membrane formation, ABC transporter proteins, and virulence in F. oxysporum were significantly down-regulated. • Strain SY41 can be used as a biocontrol agent to control A. chinensis root rot. Atractylodes chinensis is a important perennial medicinal plant in East Asia. Root rot, a devastating disease, severely reduces its yield and quality. Plant endophytes may be an effective biological control agent without detrimental effects on the environment or non-target organisms. In this study, 32 endophytic bacterial strains were isolated from healthy A. chinensis root tissues. Among them, strain SY41 exhibited the most potent inhibitory effects against F. oxysporum, F. solani , and F. redolens. Strain SY41 was identified as Bacillus licheniformis , demonstrating broad-spectrum antimicrobial activity against various phytopathogenic fungi. Additionally, strain SY41 significantly reduced the germination of pathogenic spores. Transmission electron microscopy revealed that cell-free supernatants (CFS) of strain SY41 severely damaged the cell wall structures of mycelium. VOCs produced by strain SY41 disrupted the integrity of the cell membrane of pathogenic fungi, leading to the leakage of intracellular contents. Meanwhile, they induced elevated intracellular MDA levels and the accumulation of ROS in pathogenic fungi. Transcriptome analysis indicated that the genes related to cell wall and cell membrane formation, ABC (ATP-binding cassette) transporter proteins, and virulence were significantly downregulated in F. oxysporum following VOC treatment. In summary, strain SY41 inhibited pathogenic fungi through various mechanisms of action, making it a potential candidate for controlling A. chinensis root rot.