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Extracellular ligninolytic enzyme activities in yeast isolates from wastewater treatment plants
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Many microorganisms have been found to be capable of degrading dyes; these include bacteria, filamentous fungi, yeasts, actinomycetes and algae. When compared to bacteria and filamentous fungi, yeasts present advantages; they grow rapidly and have the ability to resist unfavourable conditions. However, degradation of synthetic dyes by yeasts has not been extensively reported, namely its relation with extracellular ligninolytic enzymes. Forty six yeast strains isolated from two wastewater treatment stations along with other 81 cheese isolates were compared on their ability to decolorize five textile dyes in solid media. After a screening methodology that included liquid culture decoulorisation ability evaluation, yeasts isolates, LIII S 36 and L III ST 7 presented the best performance in the decolourisation for the five dyes tested: Remazol Black B-A, Remazol Yellow RR, Levafix Blue CA, Remazol Brilliant Blue R and Levafix® Red CA). As an attempt to understand the mechanism of decolourisation of the strains, L III ST 7 and L III S 36, spectral scanning and enzymatic activity assays were performed. It was possible observe that, depending on the dye, decolourisation might be achieved through mechanisms of either adsorption or true degradation. The presence of extracellular ligninolytic manganese peroxidase activity was detected in strains L III ST 7 and L III S 36 with an average of 2.30 and 2.06 IU. l-1, respectively; this enzymatic activity rarely demonstrated in yeasts might be related to the mechanism of true degradation as already proven for several filamentous fungi.