Shakila Nargis Khan

Abundance and diversity of Bacillus thuringiensis in Bangladesh and their cry genes profile

Bacillus thuringiensis (Bt) biopesticides, a recognized eco-friendly pest control agent, can be used to reduce many problems associated with indiscriminate use of chemical pesticides such as environmental pollutions, public health problems, emergence of resistance among pests in many developing countries etc. Bt strains were, therefore, isolated from different ecosystems of Bangladesh and characterized based on biochemical typing, 16S rRNA gene analysis, plasmid and cry genes profiles. Bt index was calculated 0.86 in this study and variations in abundance and distribution pattern of 16 different biotypes were demonstrated within 316 indigenous Bt strains which was compared to the other parts of the world. Bt indiana (17.8%), Bt kurstaki (16.7%) and Bt thuringiensis (12.7%) were found to be the most prevalent in Bangladesh among other biotypes. Hemolytic activity was variable among the biotypes and it was maximum for Bt biotype 10 (100%). Plasmids in the biotypes indiana, kurstaki, thuringiensis and israelensis were observed to occupy a wider range than other biotypes. The screening for insecticidal genes viz. cry1, cry2, cry3, cry4A, cry8, cry9, cry10 and cry11 in the native Bt strains revealed their presence in varied proportion rendering cry1, cry2 and cry3 the most abundant. The abundance of Bt strains, their diversities and the cry genes profile were thus analyzed in this study which will be the basis for further research development with Bt biopesticide in Bangladesh.

Novel Toxicity of Bacillus thuringiensis Strains against the Melon Fruit Fly, Bactrocera cucurbitae (Diptera: Tephritidae)

Bactrocera cucurbitae (melon fruit fly) is one of the most detrimental vegetable-damaging pests in Bangladesh. The toxicity of Bacillus thuringiensis (Bt) has been reported against a few genera of Bactrocera in addition to numerous other insect species. Bt strains, harbouring cry1A-type genes were, therefore, assayed in vivo against the 3(rd) instar larvae of B. cucurbitae in this study. The biotype-based prevalence of cry1 and cry1A genes was calculated to be 30.8% and 11.16%, respectively, of the test strains (n=224) while their prevalence was greatest in biotype kurstaki. Though three indigenous Bt strains from biotype kurstaki with close genetic relationship exhibited higher toxicity, maximum mortalities were recorded for Btk HD-73 (96%) and the indigenous Bt JSc1 (93%). LC50 and LC99 values were determined to be 6.81 and 8.32 for Bt JSc1, 7.30 and 7.92 for Bt SSc2, and 6.99 and 7.67 for Btk HD-73, respectively. The cause of toxicity and its variation among the strains was found to be correlated with the synergistic toxic effects of cry1, cry2, cry3 and cry9 gene products, i.e. relevant Cry proteins. The novel toxicity of the B. thuringiensis strains against B. cucurbitae revealed in the present study thus will help in developing efficient and eco-friendly control measures such as Bt biopesticides and transgenic Bt cucurbits.