Potenciais aplicações biotecnológicas de substâncias poliméricas extracelulares produzidas por bactérias isoladas de uma mina de cobre na região amazônica

Abstract

Extracellular polymeric substances are microbial products, which can be composed of proteins, lipids and, usually prevailing, polysaccharides, and that perform many roles in the microbial lifecycle. They can still be involved in the response to environmental stress factors and act protecting the cells, avoiding the activity of compounds as heavy metals through adsorbing them into functional groups in the molecule structure and so preventing the damages caused due to the penetration in the cytoplasm. Because of their roles in the surfaces colonization, some exopolymers can also be amphiphilics and act as emulsifiers. With all these properties, these compounds have a potential to be used in processes involving the heavy metal removal from the environment and the emulsification of hydrophobic substances and therefore this study aimed to identify molecules owning these features. Thereunto, the enrichment technique using lead, arsenic and cadmium (3 mmol L-1) and copper and zinc (15 mmol L-1) was used to isolate bacteria from samples gathered in a copper mine in the Amazon region and the densities varied from 2,42.103 to 1,34.108 NMP mL-1. From the 77 isolates, 45 showed exopolysaccharides production, suggesting a probable production of other extracellular polymers. The genera Bacillus and Alcaligenes prevailed, but the relative frequency from each one varied according to the sample and the metal used. The surface activity of the 45 isolates culture supernatants was analyzed for selecting three of them, identified as Actinomyces viscosus E3.Pb 5, Bacillus sp. E3.Cd 2 and Bacillus sp. E4.Cu 2. Their precipitated molecules, lipids prevailing, showed toluene emulsifying indexes higher than 50% that kept the stability after thermal treatments, in spite of a negative influence of pH and salinity. Other substrates, especially organochlorides, could be also emulsified. In the removal essays of copper and mercury from solution, the dialysis equilibrium technique showed a higher efficiency. Other experiments performed using the biomolecule produced by Bacillus sp. E4.Cu 2 verified a more intense affinity for Hg2+ ions. Furthermore, an increase in the metal concentration led to a higher amount of ions adsorbed for gram of the molecule, in spite of a decrease in the removal percentage rates. The results presented a potential use of the extracellular polymeric substances analyzed in industrial or bioremediation processes in which the evaluated properties could be exploited along with the biological nature of the compounds that suggest a higher environmental compatibility.