Screening and Characterization of Bacillus tequilensis L117: A Multifunctional Biocontrol Agent with Growth-Promoting, Antifungal, and Nematicidal Properties

Plants are highly susceptible to pathogen and pest infections, leading to severe biotic stress. Current control measures mainly rely on the excessive use of chemical pesticides, which pose significant environmental concerns. Therefore, exploring sustainable biocontrol strategies is of great importance. In this study, we screened and identified a biocontrol strain, Bacillus tequilensis L117, and systematically evaluated its antifungal, plant growth-promoting, and nematicidal properties. L117 exhibited inhibition rates ranging from 38.60% to 71.25% against eight phytopathogenic fungi. It was capable of secreting extracellular hydrolytic enzymes (cellulase, amylase, protease, and phytase) and producing siderophores and indole-3-acetic acid (IAA). Pot experiments demonstrated that L117 significantly enhanced tomato growth, leading to increased root length, fresh shoot weight, plant height, stem diameter, and flower number. Additionally, the fermentation broth, sterile filtrate, and volatile organic compounds (VOCs) of L117 exhibited nematicidal activity against Meloidogyne enterolobii, with corrected mortality rates of 85.71%, 71.43%, and 58.33%, respectively. In dual-plate assays, VOCs produced by L117 strongly inhibited Fusarium pseudograminearum (100%) and Fusarium oxysporum (63.64%). GC-MS analysis identified 20 VOCs produced by L117, including 2,4-di-tert-butylphenol, 3,5-di-tert-butylphenol, 2-methylheptanoic acid, and 3-aminopyridine, some of which have been reported to exhibit antifungal and nematicidal activity. In conclusion, L117 demonstrates multifunctional biocontrol potential, exhibiting antifungal, plant growth-promoting, and nematicidal activities. These findings highlight the potential of L117 as an eco-friendly microbial agent and provide scientific insights for plant disease management and sustainable agriculture.