Toxicity of a Brevibacillus laterosporus strain lacking parasporal crystals against Musca domestica and Aedes aegypti

The pathogenicity potential of Brevibacillus laterosporus against insects of various orders has been demonstrated and the results of recent research raise the possibility that novel strains and toxins against new insect targets may be isolated. This study investigates the toxicity of different fractions of an acrystalliferous B. laterosporus strain already known to be toxic to the housefly, against both Musca domestica and Aedes aegypti.Bacterial cultures become toxic in the stationary phase and toxicity increases and is maintained after sporulation. In our strain the spore and the canoe-shaped parasporal body (CSPB) structure seems to be the main location of toxins active against M. domestica and A. aegypti. The loss of most of the spore toxicity by heat treatment, suggests that the toxic factors are likely to be proteins. Major proteins, with a molecular weight of about 14 kDa, contained in these fractions, are probably responsible for the observed toxicity. LC50 values were 63.77 and 12.81 μg/g of diet for housefly larvae and adults, respectively, and 3.14 μg/ml for A. aegypti larvae. Based on our results, we suggest that the pathogenic activity of this B. laterosporus strain for M. domestica and A. aegypti is a toxin-mediated process reminiscent of the mechanism of action of B. thuringiensis δ-endotoxins. However, more work is needed to identify genes encoding for these proteins and to verify if toxicity is maintained when these genes are expressed by a different microrganism.