Bioefficacy of Chromobacterium piscinae against the corn leafhopper Dalbulus maidis and genomic insights into virulence factors
摘要
Chromobacterium subtsugae is the only species in this genus exploited for biological pest control. In this study, we demonstrated the insecticidal properties of Chromobacterium piscinae ESALQ6200 against Dalbulus maidis, even at low concentrations, using treatments with only bacterial cells and cell-free filtered supernatant containing secreted metabolites. Notably, we did not observe increased mortality with higher concentrations of C. piscinae ESALQ6200 cells (3.5 × 104 to 6.7 × 109 cells/mL) or cell-free filtered supernatant (1%, 25%, 100%). Mortality rates observed in the cell treatments were 76.9% (6.7 × 109 cells/mL), 75.2% (6.81 × 107 cells/mL), 78.7% (5.14 × 106 cells/mL), 77% (5.03 × 105 cells/mL), and 74.5% (3.55 × 104 cells/mL), while in the cell-free filtered supernatant treatments mortality rates were 72.9% (100%), 65.8% (25%), and 67% (1%). We believe these results may relate to effects on pest behavior, feeding inhibition, or quorum sensing in regulating virulence factors. Genomic analysis revealed several potential virulence factors, including chitinases, biosynthetic gene clusters associated with hydrogen cyanide and violacein production, and two pore-forming toxins. The digital DNA–DNA hybridization analysis indicated a high sequence identity of 96.7% between ESALQ6200 and C. piscinae (ASM2108337), well above the 70% threshold commonly applied for prokaryotic species delineation. In contrast, ESALQ6200 showed significant divergence from other Chromobacterium reference genomes, with only 51.8% sequence identity to C. subtsugae (ASM3632055). Additionally, we identified type three and six secretion systems commonly associated with virulence in various bacterial species. Our findings support the application of C. piscinae ESALQ6200 in the biological control of corn leafhoppers. Furthermore, the identification of novel Chromobacterium toxins and metabolites may facilitate the development of innovative transgenic approaches to address pest resistance to B. thuringiensis.