The Influence of Pesticides on the Spore Viability, Toxin Stability and Larvicidal Activity of Bacillus Sphaericus 2362 Strain

Abstract

In this study, 12 different commercial pesticides, including 5 fungicides, 5 herbicides, 1 aphicide and 1 acaricide, were investigated for their effects on spore viability, toxin stability and larvicidal activity of a mosquito pathogenic B. sphaericus 2362 strain. Minimal inhibitory concentrations (MICs) of each pesticide were determined after 48 h incubation of B. sphaericus 2362 strain. According to MIC results, all pesticides showed various inhibitory effects on the growth of the test bacterium. Particularly, the pesticides which contain TCA, hymexazol, copper sulphate, hexythiazox, 2,4-D Amine, copper inhibited spore germination significantly and bacterial growth even at the lowest tested concentrations. Our results indicated that various commercial pesticides in different concentrations reduced the spore viability significantly and heat-resistant spore numbers of B. sphaericus 2362 strain. In general, the pesticides decreased the spore numbers 10(4)-10(5)-fold compared to initial ones. Furthermore, it was observed that the larvicidal activity was completely lost when it was grown at the concentration of MIC values or higher. Indeed, SDS-PAGE analysis confirmed that the binary toxin proteins, 41.9 kDa and 51.4 kDa, were lost at the MIC values and higher concentrations although parasporal crystals did not disappear in the much lower pesticide concentration.