Avaliação de métodos de manutenção de Bacillus thuringiensis var. israelensis

Abstract

Due to the rising environment pollution and growth in the cases of health problems through the indiscriminate use of chemical pesticides, Bacillus thuringiensis based insecticides have been widely used as na alternative method to combat pests and vectors. Bacillus thuringiensis (also know as Bt ) is a bacterium that produces crystalline protein inclusions which are very toxic to many insect vectors and pests, and harmless to humans and animals. The proper maintenance of this microorganism is fundamental for the formulation success, therefore, the method must guarantee the highest yield of biomass and must also preserve the proteins produced by it.The most commonly used maintenance methods are with the Bt kept on the surface of paper disks, in frozen pellet, continuous filings with the lyophilized culture, and with the culture kept submerged in mineral oil. This work had as objective to determine the method that provides greater yield of bacterial biomass. Thus, three methods of maintaining Bacillus thuringiensis var. israelensis (cepa H-14/ IPA-CAV-Bti-0008): in paper disks, by freezing the pellet at -20 ºC and under mineral oil. Cultures were carried out in a bioreactor operating in batch discontinuous for each of the evaluated methods. Samples were taken every two hours to determine the growth curve of the microorganism by optical density (O.D). The analyzed parameters of pH, dissolved oxygen were automatically monitored by means of electrodes coupled to the equipment and inserted in the culture. The total yield of the bacteriaa biomass was determined by means of the flocculation / sedimentation process, with subsequent drying and determination of the dry mass. At the end of the cultures a polyacrylamide gel electrophoresis was performed to verify the profile of the proteins produced by the bacillus in each of the three methods. It was obtained that the method of preservation in mineral oil was the most efficient with regard to the higher yield of biomass, although the methods of maintenance in paper disc and the frozen pellet have the advantage of needing less storage space, risk contamination and cost.