Bacillus thuringiensis (Bt) is the most successful, environmentally-friendly, and intensively studied microbial insecticide. The major characteristic of Bt is the production of proteinaceous crystals containing toxins with specific activity against many pests including dipteran, lepidopteran, and coleopteran insects, as well as nematodes, protozoa, flukes, and mites. These crystals allow large quantities of the protein toxins to remain stable in the environment until ingested by a susceptible host. It has been previously established that 135 kDa Cry proteins have a crystallization domain at their C-terminal end. In the absence of this domain, Cry proteins often need helper proteins or other factors for crystallization. In this review, we classify the Cry proteins based on their requirements for crystallization.
Cry2Ac11, a 65 kDa insecticidal protein produced by Bacillus thuringiensis, shows toxicity against dipteran and lepidopteran larvae. It is encoded by cry2Ac11 gene ( orf3), which is part of an operon comprising orf1, orf2, and orf3. Orf2, a helper protein, helps in proper folding and prevents aberrant aggregation of newly produced molecules. In this study, we have elucidated the effect of different mutations in translation initiation region (TIR), particularly the ribosomal binding site and the start codon (RBS‐ATG) on cry2Ac11 gene expression without helper protein. All recombinant constructs were expressed in acrystalliferous B. thuringiensis subsp israelensis 4Q7 under the control of strong chimeric promoter cyt1AP/STAB. Of all the mutants, mut/RBS2, with two consecutive AUGs after the spacer region in TIR, exhibited 89‐ and 2246‐fold higher transcript levels compared with 4Q7‐operSalI/RBS ( cry2Ac11 operon) and 4Q7‐w‐RBS ( cry2Ac11 gene), respectively. The analysis of mut/RBS2 messenger RNA (mRNA) structure in the RBS‐AUG region showed the presence of RBS in the single‐stranded part of the moderately stable hairpin loop. The high expression efficiency of Cry2Ac11 mutant without helper protein is a cumulative and cooperative result of chimeric promoter cyt1AP/STAB‐SD with the optimal context of RBS‐AUG region provided by multiple AUGs and stabilizer sequence at 3′ ends.
Dengue fever is an arbo-viral infection, widespread all over the world. In 21th Century, there is no safe affordable and effective vaccine accessible yet; vector control is that most effective method for the control of the disease Objective: To determine the susceptibility status of wild and laboratory strains larvae and adults of Aedes aegypti against different group of insecticides in Lahore city. Method: From Lahore sites, larvae were collected where insecticides used for wild strain at high frequency and quantity. The Insectary of National Institute of Malaria Research and Training (NIMRT), Lahore, Pakistan, adults and larvae were collected for laboratory strain.The laboratory strains for larvae bioassays were used. The mosquitoes populations indoor and outdoor collected in 2009, hatched from larvae into adults insectary in Lahore, Pakistan. During this study, four major insecticides groups are used which include Pyrethroids (Deltamethrine 2.5% SC), Neonicotenoids (Imidacloprid 5% SC), Phenyl-pyrazoles (Fipronil 2.5% EC) and Organophosphates dichlorvos (DDVP 50% EC). For data analysis, Minitab statistical software (Version 13.20) used for data expressed as mean ± S.E.M from bioassays. By using EPA Probit, LC was estimated with 95% confidence. The 50 statistically significant p value was <= 0.05. For comparing the concentrations of insecticides, Duncan's multiple range tests was used with significant difference (5% level) using at New Costat. Results: Different location of Lahore samples, Imidacloprid the most toxic to Aedes aegypti's wild strains on the other hand while Fipronil was also active for wild larval samples. Deltamethrine showed least activity against both adults and larval strains. The susceptibility of the eld strains was lower than laboratory strains; resistant ratio varies from insecticide to insecticide. In reporting results, mosquitos' population was resistance because of infrequent and incomplete coverage. Conclusions: This study concluded that Pyrethroids and agriculture pest control play role in indirect growth of insecticides' classes. Based on this study it is suggested that by using new strategies to prevent and delay in growth of insecticides will helpful in Lahore, city, Pakistan.
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