Genetic diversity and functional characterization of endophytic Bacillus thuringiensis isolates from the North Western Indian Himalayas

Abstract

A total of 15 endophytic Bacillus thuringiensis isolates were obtained from root nodules of six legumes (soybean, ricebean, gahat, frenchbean, lentil and pea). All of these isolates were characterized by the presence of one of two different types of crystalline inclusions (spherical and bipyramidal) and tolerance to a wide pH range (4–10; optimum 7.0) and NaCl concentrations up to 8%. Genetic diversity among the B. thuringiensis isolates was determined by repetitive extragenic palindromic PCR assays (rep-PCR) using the Bacillus cereus-repetitive extragenic palindromic, BOX, enterobacterial repetitive intergenic consensus sequence and (GTG)5 primers. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis proteogram of the B. thuringiensis isolates revealed the presence of two major polypeptides (24.4 and 131.0 kDa). Maximum crystal protein profile was observed in the B. thuringiensis isolates producing the spherical crystal, while those isolates producing the bipyramidal crystal protein showed four major polypeptides (24.4, 33.8, 81.2 and 131.0 kDa). The purified crystal protein profile of the B. thuringiensis isolates revealed the presence of only one major protein of 130 kDa mass. Isolates VRB1 and VLG15 possessing the cry1 and cry2 family genes demonstrated 100% mortality against first-instar larvae of the Bihar hairy caterpillar (lepidopteran pest). Our study of the ecological and molecular diversity among newly identified B. thuringiensis isolates suggests that these could be useful in planning new strategies for integrated pest management in sustainable agricultural systems.