BACILLUS THURINGIENSIS: GENETIC DIVERSITY OF LEPIDOPTERA-SPECIFIC ISOLATES

ABSTRACT

The aim of this work was to genetically characterize 1,073 isolates of B. thuringiensis, from three Brazilian collections – UNESP/Jaboticabal, ESALQ/Piracicaba and EMBRAPA/Sete Lagoas– with the main emphasis on the analysis of the cry1 gene types presented by these isolates. To achieve this purpose, oligonucleotide primers were designed based on 16 conserved and 4 unconserved regions of the corresponding sequences from each one of the 16 subclasses of the cry1 set of genes and used in PCR amplification assays. These sequences were amplified and the presence of amplicons for each subclass was evaluated in terms of percentage of gene type per bacterial collection. As a result, 55.7% of the isolates reacted to the primer Gral cry1, and the subclasses cry1Aa, cry1Ab, cry1Ac, cry1Ad, cry1Ae, cry1Af, cry1Ag, cry1Bf, cry1Ca and cry1Fa were detected in high percentages among the isolates ranging from 43.4 to 54.9%. A subclass distribution was observed among the set of isolates from these collections, with the greater percentage of isolates harboring the cry1Ab (42.12%) and the lowest percentage for thecry1Db subclass (0.6%). The genetic variability of the analyzed bacterial collections seems to indicate the ESALQ/Piracicaba and the UNESP/Jaboticabal subsets as sources of promising isolates for the control of Lepidoptera pest insects. For the EMBRAPA/Sete Lagoas subset of isolates, in which the evaluated subclasses frequencies were considered low (below 20%), the cry1B was the most frequently observed gene type present in 38.5% of the isolates.

KEY WORDS
Genetic variability; cry gene; Bacillus thuringiensis