Abstract
Textile effluents are highly polluting and have variable and complex compositions. They can be extremely complex, with high salt concentrations and alkaline pHs. A fixed-bed bioreactor was used in the present study to simulate a textile effluent treatment, where the white-rot fungus, Trametes versicolor, efficiently decolourised the azo dye Reactive Black 5 over 28 days. This occurred under high alkaline conditions, which is unusual, but advantageous, for successful decolourisation processes. Active dye decolourisation was maintained by operation in continuous culture. Colour was eliminated during the course of operation and maximum laccase (Lcc) activity (80.2 U∙L−1) was detected after glycerol addition to the bioreactor. Lcc2 gene expression was evaluated with different carbon sources and pH values based on reverse transcriptase-PCR (polymerase chain reaction). Glycerol was shown to promote the highest lcc2 expression at pH 5.5, followed by sucrose and then glucose. The highest levels of expression occurred between three and four days, which corroborate the maximum Lcc activity observed for sucrose and glycerol on the bioreactor. These results give new insights into the use of T. versicolor in textile dye wastewater treatment with high pHs.
Highlights
Laccase (Lcc—benzenediol: oxygen oxidoreductase, EC 1.10.3.2) is a ubiquitous enzyme in nature and is widely found in higher plants, fungi, bacteria, insects and lichens [1]
The current study aims to investigate the capability of T. versicolor to decolourise RB5 under alkaline conditions in a fixed-bed bioreactor and evaluate the effect of different carbon sources and pH for lcc2 expression
The nitrogen was a limited factor during the fermentation, confirming, what is generally accepted, that a high carbon-to-nitrogen ratio is required for Lcc production in white-rot fungi (WRF)
Summary
Laccase (Lcc—benzenediol: oxygen oxidoreductase, EC 1.10.3.2) is a ubiquitous enzyme in nature and is widely found in higher plants, fungi, bacteria, insects and lichens [1]. Industrial effluents have variable composition, and in many cases are extremely complex They have few nutrients when compared to laboratory culture media and, a better knowledge on the nutrients, in particular carbon and nitrogen sources required in industrial effluents for effective biodegradation, is highly desirable. According to several authors [23,24,25], expression of this enzyme can be facilitated by regulation with metal ions, lignin related aromatic compounds and derivatives, and carbon and nitrogen. In this context, the current study aims to investigate the capability of T. versicolor to decolourise RB5 under alkaline conditions in a fixed-bed bioreactor and evaluate the effect of different carbon sources and pH for lcc expression
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