Identification of a promoter for the vegetative insecticidal protein-encoding gene vip3LB from Bacillus thuringiensis

Bacterial Vegetative Insecticidal Proteins (Vip) from Entomopathogenic Bacteria

Entomopathogenic bacteria produce insecticidal proteins that accumulate in inclusion bodies or parasporal crystals (such as the Cry and Cyt proteins) as well as insecticidal proteins that are secreted into the culture medium. Among the latter are the Vip proteins, which are divided into four families according to their amino acid identity. The Vip1 and Vip2 proteins act as binary toxins and are toxic to some members of the Coleoptera and Hemiptera. The Vip1 component is thought to bind to receptors in the membrane of the insect midgut, and the Vip2 component enters the cell, where it displays its ADP-ribosyltransferase activity against actin, preventing microfilament formation. Vip3 has no sequence similarity to Vip1 or Vip2 and is toxic to a wide variety of members of the Lepidoptera. Its mode of action has been shown to resemble that of the Cry proteins in terms of proteolytic activation, binding to the midgut epithelial membrane, and pore formation, although Vip3A proteins do not share binding sites with Cry proteins. The latter property makes them good candidates to be combined with Cry proteins in transgenic plants (Bacillus thuringiensis-treated crops [Bt crops]) to prevent or delay insect resistance and to broaden the insecticidal spectrum. There are commercially grown varieties of Bt cotton and Bt maize that express the Vip3Aa protein in combination with Cry proteins. For the most recently reported Vip4 family, no target insects have been found yet.

Bacterial Vegetative Insecticidal Proteins (Vip) from Entomopathogenic Bacteria

Entomopathogenic bacteria produce insecticidal proteins that accumulate in inclusion bodies or parasporal crystals (such as the Cry and Cyt proteins) as well as insecticidal proteins that are secreted into the culture medium. Among the latter are the Vip proteins, which are divided into four families according to their amino acid identity. The Vip1 and Vip2 proteins act as binary toxins and are toxic to some members of the Coleoptera and Hemiptera. The Vip1 component is thought to bind to receptors in the membrane of the insect midgut, and the Vip2 component enters the cell, where it displays its ADP-ribosyltransferase activity against actin, preventing microfilament formation. Vip3 has no sequence similarity to Vip1 or Vip2 and is toxic to a wide variety of members of the Lepidoptera. Its mode of action has been shown to resemble that of the Cry proteins in terms of proteolytic activation, binding to the midgut epithelial membrane, and pore formation, although Vip3A proteins do not share binding sites with Cry proteins. The latter property makes them good candidates to be combined with Cry proteins in transgenic plants (Bacillus thuringiensis-treated crops [Bt crops]) to prevent or delay insect resistance and to broaden the insecticidal spectrum. There are commercially grown varieties of Bt cotton and Bt maize that express the Vip3Aa protein in combination with Cry proteins. For the most recently reported Vip4 family, no target insects have been found yet.

Characterisation of novel Bacillus thuringiensis isolates against Aedes aegypti (Diptera: Culicidae) and Ceratitis capitata (Diptera: Tephridae)

Bacillus thuringiensis is successfully used in pest management strategies as an eco-friendly bioinsecticide. Isolation and identification of new strains with a wide variety of target pests is an ever growing field. In this paper, new B. thuringiensis isolates were investigated to search for original strains active against diptera and able to produce novel toxins that could be used as an alternative for the commercial H14 strain. Biochemical and molecular characterization revealed a remarkable diversity among the studied strains. Using the PCR method, cry4C/Da1, cry30Ea, cry39A, cry40 and cry54 genes were detected in four isolates. Three strains, BLB355, BLB196 and BUPM109, showed feeble activities against Aedes aegypti larvae. Interestingly, spore-crystal mixtures of BLB361, BLB30 and BLB237 were found to be active against Ceratitis capitata with an LC50 value of about 65.375, 51.735 and 42.972 μg cm(-2), respectively. All the studied strains exhibited important mortality levels using culture supernatants against C. capitata larvae. This suggests that these strains produce a wide range of soluble factors active against C. capitata larvae.

Spore stage expression of a vegetative insecticidal gene increase toxicity of Bacillus thuringiensis subsp. aizawai SP41 against Spodoptera exigua

To enhance the toxicity of the Bacillus thuringiensis subsp. aizawai strain SP41 (SP41), the vegetative insecticidal protein (Vip) gene vip3A from SP41 was redirected to the sporulation stage by replacing its native promoter with the strong promoter P19 of the cry11Aa operon. Compared to the wild type, SP41 with PVIP (vip3A with its native promoter and ter) had the relative expression ratios of 457, 548, and 290 at 8, 14, and 20 h of cultivation, respectively, as measured by quantitative reverse transcription polymerase chain reaction (PCR). SP41 transformed by P19VIP (vip3A controlled by P19 promoter with vip3A ter) showed higher expressions (23, 2055, 1831) at the same time points. SP41 with P19VIP20 (vip3A controlled by P19 promoter and containing P20 and operon ter) had the lowest expression levels (3, 11, 9) at any time point. SDS-PAGE analysis of proteins in the culture supernatant of the P19VIP at 8, 14, and 20 h demonstrated a significant increase in Vip3A at the sporulation stage. Using the surface contamination bioassay, the 50% lethal concentration (LC(50)) of whole culture of PVIP, P19VIP, and P19VIP20 at 20 and 48 h of cultivation against Spodoptera exigua larvae were (68.3, 21.2, and 60.2 microg cm(-2)) and (69.8, 41.8, and 74.6 microg cm(-2)), respectively, compared with 86.6 and 104.4 microg cm(-2) for SP41. The results showed that Vip from P19VIP, expressed at spore stage at 20 and 48 h, can increase the toxicity of SP41 for 4.1- and 2.5-fold, respectively.