TITLE:
Cloning of a New Truncated cry1Ac Gene from an Indian Isolate of Bacillus thuringiensis
AUTHORS:
A. Ramalakshmi, R. Manikandan, V. Balasubramani, V. Udayasuriyan
KEYWORDS:
Bacillus thuringiensis; cry1Ac; Cloning
JOURNAL NAME:
Advances in Microbiology,
Vol.4 No.1,
January
22,
2014
ABSTRACT: Transgenic Bt crops
producing insecticidal crystal proteins from Bacillus thuringiensis (Bt), so-called Cry toxins, have
proved useful in controlling insect pests. Among the cry toxins, Cry1A toxins are important because of high toxicity to lepidopteran pests and their
widespread distribution among Bt strains. In Cry1A proteins, toxin fragment is comprised of about
620 amino acids of N-terminal region and C-terminal half is not required for toxicity.
Four indigenous isolates of Bt viz., T15, T16, T20 and T31 were screened
by PCR-RFLP for 3’-truncated cry1A gene(s) corresponding to toxin fragment. RFLP analysis of cry1A amplicons obtained from the four isolates
of Bt showed presence of cry1Ac-type gene alone in three isolates. One of
the cry1Ac-postive isolates, T15 which showed
100 percent mortality in Helicoverpa armigera, was selected for cloning of DNA fragment of
about 2.1 kb containing 3’-truncated cry1Ac gene. Nucleotide sequence data generated for 3’-truncated cry1Ac gene of T15 showed 98 to 99
percent homology with 1958 bp of already reported sequences of all cry1Ac genes (cry1Ac1 to cry1Ac24). Deduced amino acid sequence of cry1Ac of Bt strain,
T15 showed one to four percent variation in comparison to all reported Cry1Ac holotypes (Cry1Ac1 to Cry1Ac24) by differing at 5 to 19 positions.
This suggests that the cry1Ac toxin of Bt isolate, T15 is a new kind of its group.