Imobilização de esporos de Bacillus subtilis em esferas de quitosana obtida de quitina de camarão para uso na biodegradação de hidrocarbonetos

Abstract

The use of microorganisms or their meta bolic products for cleaning polluted areas represents one of the most important challenges of bioremediation. However, in spite of very promising, this technology shows as main limitation the use of free microorganisms in the environment, which could fault the effectiveness from biodegradation. In those circumstances, the microorganisms are exposed to environmental conditions and can be easily dispersed from the application site, and find resistance of the indigenous microorganisms. The cells immobilization in polymers minimizes those problems providing environmental protection, maintaining the microbial population concentrated in the action site and preventing the natural competition. Several polymers have been tested in the attempt of developing supports for cells immobilization. The chitosan, a chitin derived found predominantly in the shell of crustaceans, has been studied due to its intrinsic characteristics such as high positive charges density that can interact with the cellular surfaces of many microorganisms. Besides, the chitin is the second most abundant polymer in the world after cellulose. As the main by-product of the industry of the shrimp, the choice of chitosan as immobilization matrix also represents a form of recycling these residue s from shrimp culture. In spite of those advantages, the antimicrobial effects of the chitosan have limited its utilization. To be immobilized in chitosan the microorganism has to be not only resistant to harmful effects of chitosan, but preferentially, it is necessary that it doesn't produce enzymes to degrade the polymer, such as chitosanases. Few microorganisms are known to meet that get to fill out these requirements, what explains the shortage of works dealing on immobilization of cells in chitosan. So, the aim of this work was investigat e the immobilization of bacterial spores of a Bacillus strain in chitosan spheres and evaluating, after the ge rmination of the spores, the efficiency of the cells free or immobilized to degrade n-hexadecane and produce surfactants. The results showed that the immobilization of the spores was quite viable because they resisted to the toxic effect of chitosan and to the drastic treatment of spheres production, although it was necessary supplemented the medium growth with 1% glucose in addition to 1% n-hexadecane for the germination to occur. The results of biodegradation assays showed that, in both cases, with free or immobilized cells, the n-hexadecane was consumed after 48 h of cultivation, with 98.74% and 99.51%, respectively. In spite of the biodegradation percentages be statistically similar the use of B. subtilis LAMI007 immobilized was more advantageous since the culture degraded th e same n-hexadecane concentration with the biomass ten times smaller. The immobilized cells produced the same amount of surfactants as the free cells (around 50%), but the immobilized cells did not use the surfactants produced as source of carbon. Thus could facilitate the isolation of thos e substances from the supernatant of the cultures. In conclusion, it was proven to be viable the use of the chitosan in the immobilization of B. subtilis LAMI007 spores, as well as the potential of those cells to degrade hydrocarbons and produce su rfactant, both results can be applied for decontamination of polluted areas.