Isolation and characterization of Bacillus thuringiensis strains native to Assam soil of North East India.

We have identified both crystalliferous and acrystalliferous Bt isolates from the Assam soil of North East India for the first time. A total of 301 Bacillus type colonies were selected based on their appearance and colony morphology. Out of these colonies, 42 isolates had characteristics similar to Bt isolates on MYP (Mannitol Egg Yolk Polymyxin) agar base medium. The ERIC-PCR and 16S rDNA analyses confirmed that 42 isolates are Bacillus thuringiensis. Phase contrast microscopy showed that 37 isolates produced crystal endospore during the sporulation phase and 5 acrystalliferous isolates were also found. Amplification of cry gene was carried out using general Cry primers along with one cry2 gene specific primer. Out of 42 isolates, 50% of the isolates showed presence of cry2 gene followed by cry9 (40.47) and cry1 (40.47). Moreover, 21.42% of isolates showed the presence of more than one cry genes. We also screened these isolates for the possibility of having new Bt genes using universal primer and found two strains having a new type of Cry1I gene with 82 and 85% similarities with the available Cry1I gene sequences. Thus, these new types of Bt gene could be useful for Bt-based bioformulations and generation of transgenic plants.