Metabolomics analysis reveals diverse nematicidal metabolites from spore-forming bacteria

Plant-parasitic nematodes are very important plant pathogens that can damage almost all crops worldwide. There has been a progressive decline in the use of chemical compounds because of their high toxicity to humans, livestock, and the environment. Spore-forming Bacilli as excellent biological agents are an effective and eco-friendly solution to control nematodes. However, our previous study showed that genomes of some highly nematicidal strains contain less virulent factor genes. Metabolomics studies based on mass spectrometry (MS) have shown that spore-forming strains can produce five classes of nematicidal secondary metabolites, including macrolide compounds (MCs; selamectin), triazines (Ts; prometon), piprazine derivatives (PDs; diethylcarbamazine), benzene and six-membered heterocyclic compounds (BSMHCs; crotamiton, amodiaquine and diethyltoluamide), and simple aromatic compounds (SACs; phenylacetic acid, benzyl benzoate, and benzyl alcohol). Among the spore-forming species with high nematicidal activity, Cytobacillus firmus synthesizes all five classes of nematicidal metabolites, with a ratio over 30% of PDs, BSMHCs, and SACs. Moreover, B. wiedmannii ZZQ-15, B. mycoides ZZQ-1576, and B. thuringiensis ZZQ-1522, ZZQ-1524, ZZQ-1551, ZZQ-1552, and ZZQ-1553 synthesize novel cyclopeptides with potential nematicidal activity. This study provides a useful method to identify nematicidal metabolites of bacteria.