An indigenous strain HD-550 of Bacillus thuringiensis subsp. kenyae was found to be toxic
to lepidopteran as well as dipteran insects. The cry2Aa gene (classified as
cry2Aa14) from this isolate was cloned and expressed in Escherichia coli. Only a little amount of the
expressed Cry2Aa14 protein was observed in soluble fraction under normal induction
condition. The inclusions were non-toxic to test insects, whereas solubilized Cry2Aa14 was
highly toxic to lepidopteran and dipteran insects. Cry2Aa14 protein was expressed as
thioredoxin (trx) fusion protein for improving the yield of active protein. An enhancement
of nearly 15% was observed in the yield of active Cry2Aa14. The TrxA–Cry2Aa14 protein
purified from the solubilized fraction also showed toxicity profile similar to the wild-type
protein. The LC50 values of Cry2Aa14 and TrxA–Cry2Aa14 protein against
Spodoptera litura was 694 and 696 ng/cm2, respectively, while for
Culex quinquefasciatus the LC50 values were 894 and 902 ng/ml, respectively. The broad spectrum toxicity of the Cry2Aa14 thus
indicates that this protein could be an important component in integrated pest management.
Further, the trx tag clearly led to higher yield, which facilitates protein purification
for biophysical and biochemical characterization.
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