Insecticidal activity of microencapsulated Vip3Ag4 protein in Bacillus megaterium.

Bacillus thuringiensis (Bt) produces during its vegetative growth some insecticidal proteins that are secreted and diluted into the culture medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) including binary Vpb/Vpa proteins (formerly known as Vip1/Vip2) with coleopteran activity, Vip with activity against lepidopterans and Vpb4 proteins (formerly Vip4) also with coleopteran activity. The Vip proteins are highly toxic to different species of lepidopteran pests; however, their difficulty to be produced in a concentrated form has not allowed their development as formulated biopesticides, being relegated only to be produced in transgenic crops. In this work, we demonstrated that the gene encoding Vip3Ag4 protein could be successfully expressed in an asporogenic strain of Bacillus megaterium using (D)-xylose as a low-cost inductor of protein expression. Under certain conditions (37 °C and induction with 0.5% w/v xylose), active Vip3Ag4 protein is primarily produced in soluble form remaining encapsulated within the cell wall of B. megaterium. After treatment with lugol (1% for 4 hours), induced cells were completely killed (fixed) but maintaining functional Vip3Ag4 protein, which produced above 95% mortality against first instar larvae of Chrysodeixis chalcites, Helicoverpa armigera, Spodoptera frugiperda, S. exigua, S. littoralis and Trichoplusia ni. The fact that the recombinant Vip3Ag4 protein was successfully produced in a soluble and an active form in this bacterium (with a low-cost inductor), suggest that B. megaterium is one of the hosts of choice for the production of sprayable formulations in “killed-microbial pesticides”, based on vegetative insecticidal proteins from Bt.