Harnessing <i>OmpR</i> for Enhanced Biocontrol: Characterization of a Novel Engineered Strain of <i>Lysobacter gummosus</i> with Increased Nematicidal Properties

The development of green alternatives to chemical nematicides is an urgent need in sustainable agriculture. This study constructed an engineered strain, LG209, by overexpressing the transcriptional regulator OmpR, which significantly enhanced nematicidal activity against Meloidogyne incognita J2s and increased secondary metabolite production. From its fermentation broth, 20 compounds were isolated, including a new naphthoquinone derivative. Notably, phenylacetic acid ( 3 ), 2-(4-methoxyphenyl)acetic acid ( 5 ), and 9 H -carbazole ( 18 ) exhibited strong nematicidal activity, with LC 50 values of 52.34, 88.52, and 15.18 μg/mL at 96 h, respectively. These compounds induced ROS burst and lipid peroxidation, leading to necrotic cell death in nematodes. Additionally, certain indole derivatives modulated nematode chemotaxis. In soil trials, LG209 fermentation broth achieved 68.9% control efficacy against root-knot nematode in tomato, surpassing the wild-type strain. This work provides a promising engineered strain and lead compounds for developing novel microbial nematicides.