Q-311. Toxicity Assessment of Bacillus thuringiensis Strain 4L1 Subjected at Exposure to Ultraviolet Radiation

O. M. Rutiaga_Quiñones1, M. A. Rodríguez_Pérez2, C. Lizarazo_Ortega2, J. M. Gonzalez_Prieto2, G. C. Rodriguez_Castillejos2, E. J. De Luna_Santillana2;
1Inst. Tecnologico de Durango, Durango, MEXICO, 2Ctr. de Biotecnologia Genomica, Inst. Politécnico Nacional, Reynosa Tamaulipas, MEXICO.

The biological strategy has been used for pest control. About 2000 microorganisms are considered insect pathogens, including 750 fungi, 700 viruses and about 100 bacteria. Bacillus thuringiensis is an entomopathogenic bacterium that has been applied as an agent of microbial pest control due to the presence of a crystal, containing delta-endotoxin proteins, which are synthesized during the sporulation process. The spore-crystal complex of B. thuringiensis was applied to control the maize pest Spodoptera frugiperda in the field in Mexico. Some experiments showed that violet light strongly reduced the toxic activity of crystal. Here we wonder to know if the violet light could affect the toxicity of spores, because Mexico is a plateau country with stronger sunlight. We used B. thuringiensis strain 4L1 for test. The spores derived from one colony were exposed to violet light at different duration of times. The spores developed were grown in nutritive agar plates to obtain colonies sporulated. The colonies were propagated a specific liquid media for producing a spore-crystal mixture, which can be precipitated together. Spore-crystal complex were then incorporated in the artificial diet for insects at doses of 50μg/ ml. The UV-exposed strains reduced the mortality in comparison with the native strain. The strain at intervals of 10, 20, 30, 40, 50 and 60 minute exposure resulted in a mortality of 60, 63, 50, 35, 65 and 38% respectively of insect population while the native strain caused 85% mortality. This study shows that the spore exposure to an ultraviolet source evidently affects the capability of spore to produce toxic products.