Organic-inorganic materials to immobilize biological complexes
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Organic-inorganic materials to immobilize biological complexes L. Valdez-Castro1, L. Méndez-Amaro1, R. Mendoza-Serna2, M. L. Ramírez-Castillo1 and Jorge E Ibarra3. 1
Departamento de Ingeniería en Biotecnología, Universidad Politécnica de Puebla, Tercer Carril del Ejido Serrano S/N, San Mateo Cuanalá, Juan C. Bonilla, Puebla, México. 2 Carrera de Ingeniería Química, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México, Batalla 5 de Mayo S/N, Colonia Ejército de Oriente, Iztapalapa, México. 3 Departamento Biotecnología y Bioquímica, CINVESTAV-IPN, Irapuato, Gto., México. ABSTRACT In this paper the spore-crystal complex of Bacillus thuringiensis var. israelensis (Bti) was immobilized by the sol-gel process in a hybrid polymer using as precursors the inorganic tetraethyl orthosilicate (TEOS) and the organic Polydimethylsiloxane (PDMS); in order to combine the advantages of both materials in a hybrid matrix to improve aspects such as the thermal stability, the hydrophobic properties and the porosity. Bti produces different crystals during sporulation phase; these are of protein nature and are used as bio-insecticides. It is important to mention that the insecticide attack is specific to the mosquito larva that causes dengue and black flies. The samples were characterized to ensure viability by performing growth kinetics with fermentations immersed in a flask, this microbial growth was monitored by dry weight, glucose consumption and characterized by Fourier Transform Infrared Spectroscopy (FTIR) to observe the interaction of materials with spore-crystal complex. INTRODUCTION The increasing use of biological materials in biotechnology and environmental protection has strengthened the need for microbial cultures so that the properties that make them important remain stable. Preservation of microbial strains is not easy and should ensure the viability, purity and crop genetic stability; features that match the goal of a good preservation method. Sporeproducing microorganisms can be preserved for a long time using desiccation methods, sand, silica, sterile ground, lyophilized complex or frozen at 203 K, etc. [1, 2]. The microorganism used for this study was Bacillus thuringiensis subsp. israelensis (serotype H14) which is a Gram-positive bacterium. In its growth cycle it has two phases, the vegetative growth phase where the bacterium is duplicated by bipartition and the sporulation phase during which, protein crystals known as parasporal bodies or crystals are produced. Bti has 4 protein crystals Cry 4A, Cry 4B, Cry Cyt1A and Cry 11A which are toxic for Diptera, specifically for species such as Culex, Aedes and Anhopeles, which are vectors of diseases like malaria, yellow fever and dengue. On the other hand, the advantage of this biocide is that the risk of developing mosquito resistance to Bti is very low due to its multi-toxin complex [3, 4]. The sol-gel method has proved to be a friendly process, due to the low temperature required in the process, a beneficial characteristic to immobilize bio
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