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Journal of Biological Sciences
Year: 2013  |  Volume: 13  |  Issue: 6  |  Page No.: 463 - 473

Occurrence of cry Genes in Bacillus thuringiensis (Bt) Isolates Recovered from Phylloplanes of Crops Growing in the New Delhi Region of India and Toxicity Towards Diamond-back Moth (Plutella xylostella)

S. Jayakumar and Sarvjeet Kaur    

Abstract: Bacillus thuringiensis (Bt) has been used as biopesticide sprays due to its insecticidal specificity but precipitation loss is a limitation. Bt isolates, naturally occurring on crop phylloplanes, have better on-plant persistence. Bt isolates have been isolated and characterized from phylloplanes of leguminous crops. Bt isolates, which showed presence of highly conserved 16S-23S rRNA internal transcribed spacer region, were screened by PCR for cry gene families. The cry1 gene family was found to be most abundant, followed by cry2 gene family, while none of isolates showed presence of cry3, 4, 7 and 8 gene families. Bt isolates were further screened for presence of specific genes of cry1 gene family. Four isolates-SK-222, SK-223, SK-229 and SK-232, were found to have cry1Aa, cry1Ab, cry1Ac and cry1D genes. Isolate SK-222 was found to contain maximum types of genes followed by SK-223, SK-229 and SK-232. Protein profiles of isolates by SDS-PAGE showed 130 kDa band corresponding to cry1 protein. Isolate SK-223 was most toxic followed by SK-222, SK-229 and SK-232 towards diamondback moth (Plutella xylostella) by leaf dip bioassay. Isolates SK-222 and SK-223 were significantly more toxic than Bt subsp. kurstaki (HD1). These isolates have potential of development into biopesticides. Full length cry 1Ab gene was amplified by PCR with specially designed primers from isolate SK-222, cloned and sequenced (GenBank accession No. DQ023297). Sequence analysis showed it to be identical to cry1Ab18 gene. (, GenBank accession No. AY319967) isolated previously from a Bt isolate recovered from soil of Ladakh region in this laboratory.

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