Role of Enzymes and Metabolites Produced by Bacillus spp. in the Suppression of Meloidogyne incognita in Tomato

The management of Meloidogyne incognita often depends on chemical nematicides, which pose environmental and health risks. This study investigated the potential of bacterial strains isolated from uncultivated native soil as biocontrol agents and plant growth-promoting rhizobacteria (PGPR) in tomato plants artificially infected with this nematode. Fifteen strains were screened in vitro for nematicidal and ovicidal activity, and four promising strains (307, GB16, GB24, and GB29) were selected for greenhouse trials. All strains reduced the nematode reproduction factor and the number of nematodes/g of root. Strains 307 and GB24 showed the highest reductions, 61.39 and 57.24%, respectively. Despite some positive physiological trends, Bacillus spp. did not promote a significant increase in plant growth. Metabolomic analysis revealed that the strains produced a wide range of primary metabolites with potential nematicidal activity. All strains also secreted proteases and chitinases, enzymes linked to nematode cuticle degradation. Preliminary identification based on the 16S rRNA gene and phylogenetic analysis grouped the four strains into the Bacillus subtilis group (strains GB16, GB29 and 307) or Bacillus cereus group (strain GB24); however, genome sequencing will be required in future studies. Overall, strains 307 and GB24 demonstrated strong biocontrol potential, supporting their use as sustainable and complementary alternatives to chemical nematicides.