Contribution of Lysinibacillus sphaericus hemolysin and chitin-binding protein in entomopathogenic activity against insecticide resistant Aedes aegypti

Given its toxicity against culicid larvae, Lysinibacillus sphaericus is used for the biological control of mosquitoes such as Culex sp. and Anopheles sp. The toxicity factors currently reported for L. sphaericus include the Binary toxin, Mtx toxins, and the S-layer. However, Aedes aegypti is refractory to the Binary toxin, the most toxic larvicidal protein of L. sphaericus. Until now, there are no evidences of the hemolytic and chitinolytic capacity of L. sphaericus. Herein, the expression of the hemolysin D (hlyD) and the chitin-binding protein genes of L. sphaericus III(3)7, OT4b.25, and 2362 was quantified. Gene expression was assessed 24 and 48 h after field-collected and Rockefeller A. aegypti larvae were fed with the bacteria. The hlyD gene showed the highest expression at 24 h whilst the expression of the chitin-binding protein gene increases at 48 h. The highest hlyD expression was seen in the III(3)7 strain and the highest chitin-binding protein gene expression was in the 2362 strain. The consortium of L. sphaericus III(3)7 and 2362 showed the highest expression of both genes being with field-collected and Rockefeller larvae. The results suggest that hemolysin D and the chitin-binding protein can be two novel toxic elements involved in the entomopathogenic activity of L. sphaericus. These proteins, along with the other L. sphaericus toxins, make this bacterium a suitable alternative to replace the chemical insecticides used for the control of A. aegypti populations.