CLONING AND EXPRESSION OF THE BACILLUS-SPHAERICUS-2362 MOSQUITOCIDAL GENES IN A NONTOXIC UNICELLULAR CYANOBACTERIUM, SYNECHOCOCCUS PCC6301

Genes encoding the mosquitocidal binary toxin of Bacillus sphaericus 2 362 were introduced into Synechococcus PCC6301, a cyanobacterium that can tolerate a number of potential variations in the mosquito breeding environment, and can serve as a food source for mosquito larvae. The toxin genes, preceded by a Synechococcus rbcL promoter, were located o n a mobilizable Escherichia coli Synechococcus shuttle vector, which w as introduced into Synechococcus PCC6301 at frequencies of 10(-5)-10(- 7) exconjugants/recipient, depending on the selective conditions used. Recombinant Synechococcus exhibited significant toxicity against 2-da y-old and 6-day-old Culex quinquefasciatus larvae, the concentration r equired to kill 50% of larvae (LC50) being 2.1 x 10(5) and 1.3 x 10(5) cells/ml respectively. Mosquitocidal activity decreased tenfold after 20 generations of non-selective growth.