Biochemical characterization of a novel azo reductase named BVU5 from the bacterial flora DDMZ1: application for decolorization of azo dyes

The combination of BVU5 enzyme and coenzyme NADH can quickly degrade the azo dye RB5.

Enzymatic Degradation of Azo Bonds and Other Functional Groups on Commercial Silk Dyes by Streptomyces coelicoflavus CS-29

Azo dyes are used for silk textile manufacture, where their decolorization and detoxication are necessary after initial dying in the craft industry. The bio-decolorization efficiency of Streptomyces coelicoflavus CS-29 toward commercial azo blue and red dyes was investigated, analyzing the degradation and adsorption of dye molecules. S. coelicoflavus CS-29 showed reductions of 70% and 51% in red and blue dyes, respectively, after seven days. Morphological observation by light microscopy showed that dye molecules were adsorbed onto S. coelicoflavus CS-29 cell surface to form a dense cell pellet. Moreover, peroxidase and laccase activity were detected as extracellular enzymes, but no azo-reductase was detected. From the enzymatic activity, changes of dye profiles in HPLC showed differences between control dyes (untreated dyes) and metabolized products of dyes treated with S. coelicoflavus CS-29. The presence of main functional azo groups (-N=N-) in both blue and red silk dyes was indicated by FTIR analysis, in the untreated azo dyes. The azo bonds seemed to disappear in metabolites after S. coelicoflavus CS-29 treatment and other functional groups were changed compared to the control dyes. The treated dyes showed no significant effect on seed germination, root length, and shoot length of mung beans during phytotoxicity analysis. The red dyes showed a more negative effect on shoot lengths than the blue dyes. The overall results showed that S. coelicoflavus CS-29 is an effective and promising tool for the treatment of dye contaminated wastewater and the permanent elimination of recalcitrant commercial azo dye pollutants.

Synergistic effect of biological and advanced oxidation process treatment in the biodegradation of Remazol yellow RR dye

The current study investigated the efficiency of synergistic biological and Advanced Oxidation Process (AOPs) treatment (B-AOPs) using Aeromonas hydrophila SK16 and AOPs-H2O2 in the removal of Remazol Yellow RR dye. Singly, A. hydrophila and AOPs showed 90 and 63.07% decolourization of Remazol Yellow RR dye (100 mg L−1) at pH 6 and ambient temperature within 9 h respectively. However, the synergistic B-AOPs treatments showed maximum decolorization of Remazol Yellow RR dye within 4 h. Furthermore, the synergistic treatment significantly reduced BOD and COD of the textile wastewater by 84.88 and 82.76% respectively. Increased levels in laccase, tyrosinase, veratryl alcohol oxidase, lignin peroxidase and azo reductase activities further affirmed the role played by enzymes during degradation of the dye. UV–Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC) and gas chromatography–mass spectroscopy (GC–MS) confirmed the biotransformation of dye. A metabolic pathway was proposed based on enzyme activities and metabolites obtained after GC–MS analysis. Therefore, this study affirmed the efficiency of combined biological and AOPs in the treatment of dyes and textile wastewaters in comparison with other methods.

Metabolite Identification from Biodegradation of Congo Red by Pichia sp.

Azo dyes are commonly used in textile and paper industries. However, its improper disposal often results in polluting water bodies. Azo dyes can cause adverse health effects because of its carcinogenic properties. Various methods to remove azo dyes from water have been proposed, including biological methods such as biosorption and biodegradation. Biosorption and biodegradation were done by using bacteria, yeast or mold. In general, yeasts have some advantages for azo dyes degradation due to its faster growth compared to mold and better resistance against unfavorable environment compared to bacteria. Previously, we observed that yeast Pichia sp. have the ability to degrade Congo red, an azo dye. However, information regarding biodegradation of azo dyes by Pichia sp. are still limited. Therefore, in this study, we showed degradation of Congo red by Pichia sp. crude enzyme extract obtained from separating Pichia cells from medium by centrifugation, followed by identification of its biodegradation products. Biodegradation product was separated from enzyme by ethyl acetate and then Gas Chromatography-Mass Spectroscopy (GC-MS) method was employed to identify biodegradation product. Chromatogram results of GC-MS showed that Congo red were degraded into various products such as biphenyl, naphthalene and smaller molecules with 94 m/z and 51 m/z. These results suggest involvement of azo reductase and laccase-like enzymes which cleaves azo bonds and oxidize the dye molecules to smaller molecules. This study implies the use of Pichia sp. as a bioremediation agent for the removal of azo dyes. Keywords: Biodegradation, Congo red, Pichia sp., metabolite identification, GC-MS

Novel fluorescent amphiphilic copolymer probes containing azo-tetraphenylethylene bridges for azoreductase-triggered release

A novel AIE fluorescent probe of amphiphilic block copolymer PCL-TPE-Azo-PEG was successfully synthesized based on azo reductase response. The polymer can be self-assembled and showed fluorescence improvement during reductant-triggered release.

Reduction of azo dyes by flavin reductase from Citrobacter freundii A1

<em>Citrobacter freundii </em>A1 isolated from a sewage treatment facility was demonstrated to be able to effectively decolorize azo dyes as pure and mixed culture. This study reports on the investigation on the enzymatic systems involved. An assay performed suggested the possible involvement of flavin reductase (Fre) as an azo reductase. A heterologouslyexpressed recombinant Fre from <em>C. freundii </em>A1 was used to investigate its involvement in the azo reduction process. Three model dyes were used, namely Acid Red 27 (AR27), Direct Blue 15 (DB15) and Reactive Black 5 (RB5). AR27 was found to be reduced the fastest by Fre, followed by RB5, and lastly DB15. Redox mediators nicotinamide adenine dinucleotide (NADH) and riboflavin enhance the reduction, suggesting the redox activity of the enzyme. The rate and extent of reduction of the model dyes correlate well with the reduction potentials (<em>E</em>_p). The data presented here strongly suggest that Fre is one of the enzymes responsible for azo reduction in <em>C. freundii </em>A1, acting via an oxidation-reduction reaction.

Azo Reductase Activity of Intact Saccharomyces cerevisiae Cells Is Dependent on the Fre1p Component of Plasma Membrane Ferric Reductase

ABSTRACT Unspecific bacterial reduction of azo dyes is a process widely studied in correlation with the biological treatment of colored wastewaters, but the enzyme system associated with this bacterial capability has never been positively identified. Several ascomycete yeast strains display similar decolorizing behaviors. The yeast-mediated process requires an alternative carbon and energy source and is independent of previous exposure to the dyes. When substrate dyes are polar, their reduction is extracellular, strongly suggesting the involvement of an externally directed plasma membrane redox system. The present work demonstrates that, in Saccharomyces cerevisiae, the ferric reductase system participates in the extracellular reduction of azo dyes. The S. cerevisiae Δfre1 and Δfre1 Δfre2 mutant strains, but not the Δfre2 strain, showed much-reduced decolorizing capabilities. The FRE1 gene complemented the phenotype of S. cerevisiae Δfre1 cells, restoring the ability to grow in medium without externally added iron and to decolorize the dye, following a pattern similar to the one observed in the wild-type strain. These results suggest that under the conditions tested, Fre1p is a major component of the azo reductase activity.