Diversidade e aplicações biotecnológicas de leveduras e fungos filamentosos presentes em ambientes aquáticos contaminados com arsênio

Abstract

The increase in industrial activities has intensified environmental pollution problems and deterioration of several ecosystems with the accumulation of many pollutants such as heavy metals and metalloids, among them arsenic, a carcinogenic metalloid. The main objective of this study was to study yeast and filamentous fungi diversity in the freshwater environments contaminated with arsenic at the region of Córrego da Mina in Nova Lima, Brazil and use isolated yeasts as biosorbents like free and immobilized cells on macroporous alumina spheres. The water samples were collected from July 2007 to July 2008 at three different points, three water samples of 500 mL were collected at each point. From these samples were identified following genera of yeasts, Hanseniaspora, Candida, Acremonium, Pichia, Rhodotorula, Aureobasidium, Geotrichum, Rhodosporidium, Issatchenkia, Kodamaea, Trichosporon and Cryptococcus. Ascomycetous yeasts were more frequently isolated in this work at all points and all collections. From these samples were identified following genera of filamentous fungi Paraconiothyrium, Curvularia, Fusarium, Cladosporium, Plectosphaerella, Leptosphaeria, Penicillium, Hypocrea, Alternaria, Microsphaeropsis, Epicoccum, Stemphylium, Rhizomucor, Neurospora, Amylomyces, Aspergillus, Pestalotiopsis, Cochliobolus, Mucor, Cylindrocladiella, Bionectria, Phaeosphaeria, Microdochium, Phoma, Discostroma, Daldinia and Bipolaris. In addition, some strains were identified by order as Pleosporales sp. and by class as Dothideomycetes sp. Most yeast isolates tested for tolerance to As (V) in this study showed the tolerance limit of up to 100 mM of As (V), on the other hand most of the isolates of filamentous fungi, about 51% of isolates, grew only on YM agar not supplemented with As (V). Rhodosporidium toruloides L56-1 was the only one that remained viable after the tolerance test in YM broth supplemented with As (V) up to a 300 mM As (V) concentration. It was chosen with other yeasts that had tolerated high As (V) concentrations to perform immobilization experiments on macroporous alumina spheres. In this work was developed a chemical process for agglomerating microparticles of activated alumina, which is based on a sol-gel process. The developed process preserves the porosity of the alumina microparticles and introduces macropores in the resulting sphere. The cells of R. toruloides L56-1 immobilized in gel spheres showed the highest removal efficiency (97.11%) compared with other yeast cells immobilized in dry spheres. This increase in adsorption can be explained by the preservation of hydrphilicity in gel spheres and preservation of nanoparticles of alumina in form of aluminm hydroxide. This enables a hydrofilicity increase the accessibility of arsenic and thus increasing its concentration gradient in the active sites of alumina and immobilized cells. The approach taken in this work, through the study of diversity and tolerance to As (V) of yeast and filamentous fungi, isolated from aquatic environments contaminated with As and allowed selection among the same isolates to develop an innovative compound containing adsorbent yeast cells immobilized on alumina spheres with activated carbon, which was effective in removing As (V) from water.