Bacillus sphaericus Mtx1 and Mtx2 toxins co-expressed in Escherichia coli are synergistic against Aedes aegypti larvae

Abstract

Mtx1 and Mtx2 are mosquitocidal toxins produced by some strains of Bacillus sphaericus during vegetative phase of growth. Mtx1 from B. sphaericus 2297 shows higher toxicity against Culex quinquefasciatus larvae than to Aedes aegypti larvae whereas Mtx2 from B. sphaericus 2297 shows lower toxicity against C. quinquefasciatus than to A. aegypti larvae. To test synergism of these toxins against A. aegypti larvae, mtx1 and mtx2 genes were cloned into a single plasmid and expressed in Escherichia coli. Cells producing both Mtx1 and Mtx2 toxins exhibited high synergistic activity against A. aegypti larvae approximately 10 times compared to cells expressing only a single toxin. Co-expression of both toxins offers an alternative to improve efficacy of recombinant bacterial insecticides. There is a high possibility to develop these toxins to be used as an environmentally friendly mosquito control agent.

Efficacy of the vegetative cells of Lysinibacillus sphaericus for biological control of insecticide-resistant Aedes aegypti

“…Although S-layer and Mtx toxins have shown entomopathogenic activity [16, 18], these do not have the properties of a biological controller. Meanwhile, the vegetative cells of L. sphaericus can persist and recycle in the environment.…”

“…Recombinant Mtx toxins and S-layer protein have been assessed against Ae. aegypti larvae [16, 18], but there are no reports regarding the whole vegetative cell. Recent genomic studies have revealed that some L. sphaericus strains have hemolysins and chitinases genes, which could play an important role in the entomopathogenic activity of these strains [19–21].…”

The bacterium, Lysinibacillus sphaericus, as an insect pathogen

“…Both the vegetative toxins Mtx1 and Mtx2 are able to act in synergism against Aedes aegypti (Rungrod et al, 2009) and each acts synergistically with the Bin toxin (Wirth et al, 2007) and may be valuable in enhancing the effectiveness of L. sphaericus spore preparations. Although the Mtx proteins are produced during vegetative growth and Bin proteins are associated with the spores, it has been shown that, in intoxicated insects, most L. sphaericus have entered vegetative growth by the time that the larvae die (Charles, 1987).…”

Potential of bacterial derived biopesticides in pest management

“…These are (1) the binary toxin (Bin) composed of two proteins of 42 kDa (BinA) and 51 kDa (BinB), which are synthesized during sporulation and co-crystallize, (2) the soluble mosquitocidal toxins (Mtx1, Mtx2 and Mtx3) produced during vegetative growth and (3) the two-component crystal toxin (Cry48Aa1/Cry49Aa1). Rungrod et al (2009) reported the synergistic activity of Mtx1 and Mtx2 toxins against A. aegypti (Diptera: Culicidae) larvae. Jones et al (2008) reported the highly restricted target specificity of the Cry48Aa-Cry49Aa binary toxin from B. sphaericus towards C. quinquefasciatus mosquito larvae (Diptera: Culicidae) with non-toxicity to Coleopteran, Lepidopteran and other Dipteran insects including closely related Aedes and Anopheles mosquitoes.…”