THE INTRODUCTION INTO BACILLUS-SPHAERICUS OF THE BACILLUS-THURINGIENSIS SUBSP MEDELLIN CYT1AB1 GENE RESULTS IN HIGHER SUSCEPTIBILITY OF RESISTANT MOSQUITO LARVA POPULATIONS TO BACILLUS-SPHAERICUS

The fragment containing the gene encoding the cytolytic Cyt1Ab1 protei n from Bacillus thuringiensis subsp, medellin and its flanking sequenc es (I, Thiery, A. Delecluse, M. C, Tamayo, and S. Orduz, Appl, Environ , Microbiol. 63:468-473, 1997) was introduced into Bacillus sphaericus toxic strains 2362, 2297, and Iab872 by electroporation with the shut tle vector pMK3. Only small amounts of the protein were produced in re combinant strains 2362 and Iab872, The protein was detected in these s trains only by Western blotting and immunodetection with antibody rais ed against Cyt1Ab1 protein. Large amounts of Cyt1Ab1 protein were prod uced in B. sphaericus recombinant strain 2297, and there was an additi onal crystal, other than that of the binary toxin, within the exospori um, The production of the Cyt1Ab1 protein in addition to the binary to xin did not increase the larvicidal activity of the B. sphaericus reco mbinant strain against susceptible mosquito populations of Culex pipie ns or Aedes aegypti. However, it partially restored (10 to 20 times) s usceptibility of the resistant mosquito populations of C, pipiens (SPH AE) and Culex quinquefasciatus (GeoR) to the binary toxin, The Cyt1Ab1 protein produced in recombinant B. thuringiensis SPL407(pcyt1Ab1) was synthesized in two types of crystal-one round and with various dense areas, surrounded by an envelope, and the other a regular cuboid cryst al, very similar to that found in the B. sphaericus recombinant strain .