Diversity of lepidopteran specific Bacillus thuringiensis strains from Argentina

M.E. VIDAL DOMÍNGUEZ; L.M. DÍAZ; G.L. SALERNO; C.M. BERÓN

San Miguel de Tucumán

Congreso; VII Congreso Argentino de Microbiología General; 2011

Sociedad Argentina de Microbiología General

Several lepidopteran species cause significant damage to many agricultural important crops in Argentina. Among them Anticarsia gemmatalis and Spodoptera frugiperda are important insect pests of soybean, corn, wheat, and forage grasses. Currently, the use of entomopathogenic bacteria Bacillus thuringiensis as biolarvicide offers a viable alternative for insect control. This bacterium produces proteinaceous inclusions during sporulation that are toxic towards insect larvae upon ingestion. The parasporal body of B. thuringiensis consists of one or more insecticidal crystal proteins (ICP). Most ICP-coding genes are located in megaplasmids. Typically, B. thuringiensis harbours a set of native plasmids, which vary in number from 1 to 17 and in size from 2 kb to 600 kb. Plasmid patterns and different PCR approaches have frequently been used to characterize B. thuringiensis strains around the world. In this work, we described the characterization of nine B. thuringiensis strains isolated from soil samples of Argentina. In preliminary tests, we performed mortality assays to determine the toxicity spectrum of these strains. They were highly toxic against A. gemmatalis and moderately toxic against S. frugiperda. Also, protein patterns of spore-crystal complexes analyzed by SDS-PAGE showed similar patterns with major polypeptides of about 70 and 130 kDa. Molecular characterization of these strains was made by determining plasmid patterns, nested-PCR and, denaturing gradient gel electrophoresis (DGGE). According their plasmidic pattern, the isolates were classified in three groups containing four, eight or no plasmids. On the other hand, characterization of cry gene content in these strains was performed by a nested-PCR and DGGE approaches both with degenerate primers. Using DGGE methodology we got identical profiles in eight strains except in strain FCC25. Additionally, these methods allowed us to identify partial cry sequences that are currently under analysis and will be further used to recognize and characterize new cry sequences.