ABSTRACT
A total of 268 Bacillus thuringiensis strains obtained from different sources of Argentina were analyzed to determine the diversity and distribution of the cryl, cry2, cry8, cry9 and vip3A genes encoding for lepidopteran-specific insecticidal proteins. Twin strains were excluded. Ten different profiles were detected among the 80 selected B. thuringiensis strains. Two of these profiles (cry1Aa, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa (35/80), and cry1Aa, cry1Ab, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa (25/80)) pooled 75% of the strains. The existence of this low diversity is rare, since in most of the studied collections a great diversity of insecticidal toxin gene profiles has been described. In addition, the most frequently detected profile was also most frequently derived from soil (70%), stored product dust (59%) and spider webs (50%). In contrast, the cry1Aa, cry1Ab, cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa profiles were mainly detected in strains isolated from leaves (40%) and dead insect larvae (50%). Six of the identified insecticidal toxin gene profiles were discovered in strains isolated from stored product dust and leaves indicating higher diversity of profiles in these kinds of sources than in others. Some strains with high insecticidal activity against Epinotia aporema (Lepidoptera) larvae were identified, which is important to explore future microbial strategies for the control of this crop pest in the region.
Se analizaron 268 cepas de Bacillus thuringiensis obtenidas de diferentes fuentes de Argentina con el objeto de determinar la diversidad y distribución de genes cryl, cry2, cry8, cry9 y vip3A, que codifican proteínas insecticidas lepidóptero-específicas. Se excluyeron las cepas gemelas. Se detectaron solo diez perfiles diferentes entre los 80 B. thuringiensis seleccionados. Dos de estos perfiles, el cry1Aa, cry1Ac, crylIa, cry2Aa, cry2Ab y vip3Aa (35/80) y el cry1Aa, cry1Ab, cry1Ac, crylIa, cry2Aa, cry2Ab y vip3Aa (25/80), comprendieron el 75% de las cepas seleccionadas. La existencia de esta baja diversidad es una rareza, ya que en la mayor parte de las colecciones estudiadas se ha descrito una gran diversidad de perfiles de genes de toxinas insecticidas. El perfil detectado con mayor frecuencia se obtuvo principalmente de cepas procedentes de suelo (el 70% de los de esa fuente lo tenían), también fue mayoritario entre los procedentes de polvo de producto almacenado (59%) y en los que procedían de telas de arana (50%). En cambio, el perfil cry1Aa, cry1Ab, cry1Ac, crylIa, cry2Aa, cry2Ab y vip3Aa se detectó principalmente en las cepas aisladas de hojas (40%) y de larvas de insectos muertos (50%). Seis de los perfiles identificados fueron encontrados en cepas aisladas de polvo de producto almacenado y de hojas, lo que indica una mayor diversidad de perfiles en estas fuentes que en otras. Se identificaron algunas cepas con alta actividad insecticida contra larvas de Epinotia aporema (Lepidoptera), hallazgo importante para explorar en el futuro estrategias microbianas para el control de esta plaga en la región.
Subject(s)
Animals , Bacillus thuringiensis , Bacterial Toxins , Genes, Bacterial , Hemolysin Proteins , Argentina , Bacillus thuringiensis/genetics , Bacillus thuringiensis/pathogenicity , Bacterial Proteins , Bacterial Toxins/genetics , Pest Control, Biological , Endotoxins , Hemolysin Proteins/physiology , Hemolysin Proteins/genetics , Larva , LepidopteraABSTRACT
We report the characterization of an Argentine isolate of Bacillus thuringiensis (INTA TA24-6) similar to the HD-1 strain, which harbors a cryptic cry2Ab gene that apparently is transcribed but not translated into a protein. INTA TA24-6 showed a Rep-PCR pattern identical to the HD-1 strain, a plasmid pattern that resembled that of this strain and cry1 and cry2 genes as HD-1. Screening of cry1 and cry2 genes showed that INTA TA24-6 harbors only cry1Ac and cry2Ab genes. Furthermore, crystalline inclusions of INTA TA24-6 exhibit a bipyramidal shape, typical of Lepidoptera-active B. thuringiensis strains, containing a major protein of ca. 130 kDa toxic to Epinotia aporema Wals. (Lepidoptera: Tortricidae) larvae. Neither the flat-square to cuboidal crystal nor a ca. 65 kDa protein typical of strains expressing Cry2 proteins were detected in INTA TA24-6. In agreement with this information, parasporal crystals of INTA TA24-6 did not show toxicity to Aedes aegypti L. (Diptera:Culicidae) larvae. Gene transcription analyses suggested that the cry2A gene might be cryptic in INTA TA24-6 despite its transcription at different sporulation stages.