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Appl. Environ. Microbiol., 11 1997, 4413-4420, Vol 63, No. 11
S Poncet, C Bernard, E Dervyn, J Cayley, A Klier and G Rapoport
Integrative plasmids were constructed to enable integration of foreign DNA
into the chromosome of Bacillus sphaericus 2297 by in vivo recombination.
Integration of the aphA3 kanamycin resistance gene by a two-step procedure
demonstrated that this strategy was applicable with antibiotic resistance
selection. Hybridization experiments evidenced two copies of the operon
encoding the binary toxin from B. sphaericus in the recipient strain. The
Bacillus thuringiensis subsp. israelensis cry11Aal gene (referred to as
cry11A), encoding a delta-endotoxin with toxicity against Culex, Aedes, and
Anopheles larvae, was integrated either by a single crossover event [strain
2297 (::pHT5601), harboring the entire recombinant plasmid] or by two
successive crossover events [strain 2297 (::cry11A)]. The level of the
Cry11A production in B. sphaericus was high; two crystalline inclusions
were produced in strain 2297 (::pHT5601). Synthesis of the Cry11A toxin
conferred toxicity to the recombinant strains against Aedes aegypti larvae,
for which the parental strain was not toxic. Interestingly, the level of
larvicidal activity of strain 2297 (::pHT5601) against Anopheles stephensi
was as high as that of B. thuringiensis subsp. israelensis and suggested
synergy between the B. thuringiensis and B. sphaericus toxins. The
toxicities of parental and recombinant B. sphaericus strains against Culex
quinquefasciatus were similar, but the recombinant strains killed the
larvae more rapidly. The production of the Cry11A toxin in B. sphaericus
also partially restored toxicity for C. quinquefasciatus larvae from a
population resistant to B. sphaericus 1593. In vivo recombination therefore
appears to be a promising approach to the creation of new B. sphaericus
strains for vector control.
Copyright © 1997, American Society for Microbiology
Improvement of Bacillus sphaericus toxicity against dipteran larvae by integration, via homologous recombination, of the Cry11A toxin gene from Bacillus thuringiensis subsp. israelensis
Unite de Biochimie Microbienne, URA 1300 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France. sponcet@biotec.jouy.inra.fr
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