Expression of mosquito active toxin genes by a Colombian native strain of the gram-negative bacterium Asticcacaulis excentricus

Mosquito control with biological insecticides, such as Bacillus sp. toxins, has been used widely in many countries. However, rapid sedimentation away from the mosquito larvae feeding zone causes a low residual effect. In orde r to overcome this problem, it has been proposed to clone the Bacillus toxi n genes in aquatic bacteria which are able to live in the upper part of the water column. Two strains of Asticcacaulis excentricus were chosen to intr oduce the B. sphaericus binary toxin gene and B. thuringiensis subsp. medel lin cry11Bb gene cloned in suitable vectors. In feeding experiments with th ese aquatic bacteria, it was shown that Culex quinquefasciatus, Aedes aegyp ti, and Anopheles albimanus larvae were able to survive on a diet based on this wild bacterium. A. excentricus recombinant strains were able to expres s both genes, but the recombinant strain expressing the B. sphaericus binar y toxin was toxic to mosquito larvae. Crude protease A. excentricus extract s did not degrade the Cry11Bb toxin. The flotability studies indicated that the recombinant A. excentricus strains remained in the upper part of the w ater column longer than the wild type Bacillus strains.