Characterization and biological activity of Bacillus thuringiensis isolates that are potentially useful in insect pest control

Abstract

The current study shows a screening of 490 samples from 40 different agricultural environments in Argentina for B. thuringiensis strains that exhibited toxicity against Lepidoptera. Fourteen strains of B. thuringiensis isolated from both larvae showing disease symptoms and soil samples were phenotypically, genetically and biologically characterized. Analysis of larvicidal activity indicated that three isolates exhibited high toxicity against lepidopteran larvae; this toxicity was in most, higher than that of the reference strain B. thuringiensis 4D1. This strong biological effect was represented by both a higher mortality which reached 100% -in B. thuringiensis RT- and a shorter LT50. In addition, molecular characterization showed that this isolate carried a cry gene content different to the others native B. thuringiensis and B. thuringiensis 4D1. Protein profile analysis of whole-cell proteins not only allowed the differentiation of B. thuringiensis but also revealed the possibility of applying protein profile analysis in classification of toxicity patterns. Cluster analysis showed that there were two main groups. Interestingly, one of them only contained the most pathogenic native strains. In addition, phenotypic characterization allowed differentiation among the strains by means of their extracellular esterase profiles. Lytic activity that would contribute to B. thuringiensis effectiveness was also determined. Analyses like those presented in the current study are essential to identify the most toxic strains and to allow the exploitation of local biodiversity for its application in biological control programmes.