Decolorization of textile azo dyes by aerobic bacterial consortium

The decolorization potential of two bacterial consortia developed from a textile wastewater treatment plant showed that among the two mixed bacterial culture SKB-II was the most efficient in decolorizing individual as well as mixture of dyes. At 1.3 g L^?1 starch supplementation in the basal medium by the end of 120 h decolorization of 80–96% of four out of the six individual azo dyes Congo red, Bordeaux, Ranocid Fast Blue and Blue BCC (10 mg L^?1) was noted. The culture exhibited good potential ability in decolorizing 50–60% of all the dyes (Congo red, Bordeaux, Ranocid Fast Blue and Blue BCC) when present as a mixture at 10 mg L^?1. The consortium SKB-II consisted of five different bacterial types identified by 16S rDNA sequence alignment as Bacillus vallismortis, Bacillus pumilus, Bacillus cereus, Bacillus subtilis and Bacillus megaterium which were further tested to decolorize dyes. The efficient ability of this developed consortium SKB-II to decolorize individual dyes and textile effluent using packed bed reactors is being carried out.     

Decolorization of 1-amino-4-bromoanthraquinone-2-sulfonic acid by a newly isolated strain of Sphingomonas herbicidovorans

A novel isolate of Sphingomonas herbicidovorans could decolorize 1-amino-4-bromoanthraquinone-2-sulfonic acid (bromoamine acid, BAA), an intermediate of anthraquinone dyes, and grow with it as the sole source of carbon. The strain was identified by 16S rRNA gene sequencing and physiological-biochemical test. The optimal condition for both decolorization and cell growth was found at temperature of 30 °C and pH 7.0, respectively. Furthermore, the decolorization efficiency could be enhanced with higher shaking speed. The percentage of BAA decolorization could be over 98% within 24 h even for the initial concentration greater than 1000 mg l^?1. The decolorization kinetics could be reasonably described by the Monod equation. Additional carbon sources such as glucose could enhance the decolorization rate. During the decolorization process, the molecular of BAA cleaved, releasing phthalic acid and an end product which might be benzene derivative substituted by amino, bromo, hydroxyl and sulfonate groups according to the infrared spectral analysis.     

Degradation of synthetic reactive azo dyes and treatment of textile wastewater by a fungi consortium reactor

In this paper, two microbial cultures with high decolorization efficiencies of reactive dyes were obtained and were proved to be dominant with fungi consortium in which 21 fungal strains were isolated and 8 of them showed significant decolorization effect to reactive red M-3BE. A 4.5 l continuous biofilm reactor was established using the mixed cultures to investigate the decolorization performance and the system stability under the conditions of simulated and real textile wastewater as influents. The optimal nutrient feed to this bioreactor was 0.5 g l⁻¹ glucose and 0.1 g l⁻¹ (NH₄)₂SO₄ when 30 mg l⁻¹ reactive black 5 was used as initial dye concentrations. Dye mineralization rates of 50–75% and color removal efficiencies of 70–80% were obtained at 12 h hydraulic retention time (HRT) in this case. Higher glucose concentrations in the influents could significantly improve color removal, but was not helpful for dye mineralization. Besides reactive black 5, the bioreactor could effectively decolorize reactive red M-3BE, acid red 249 and real textile wastewater with efficiency of 65%, 94% and 89%, respectively. In addition, the microbial community on the biofilm was monitored in the whole running process. The results indicated fungi as a dominant population in the decolorization system with the ratio of fungi to bacteria 6.8:1 to 51.8:1 under all the tested influent conditions. Analysis of molecular biological detection indicated that yeasts of genus Candida occupied 70% in the fungal clone library based on 26S rRNA gene sequences.     

Treatment of dye-rich wastewater by an immobilized thermophilic cyanobacterial strain: Phormidium sp.

The removal of Remazol Blue and Reactive Black B by the immobilized thermophilic cyanobacterial strain Phormidium sp. was investigated under thermophilic conditions in a batch system, in order to determine the optimal conditions required for the highest dye removal. In the experiments, performed at pH 8.5, with different initial dye concentrations between 9.1 mg l⁻¹ and 82.1 mg l⁻¹ and at 45 °C, calcium alginate immobilized Phormidium sp. showed high dye decolorization, with maximum uptake yields ranging from 50% to 88% at all dye concentrations tested. When the effects of high dye concentrations on dye removal were investigated, the highest uptake yield in the beads was 50.3% for 82.1 mg l⁻¹ Remazol Blue and 60.0% for 79.5 mg l⁻¹ Reactive Black B. The highest color removal was detected at 45 °C and 50 °C incubation temperatures for all dye concentrations. As the temperature decreased, the removal yield of immobilized Phormidium sp. also decreased. At about 75 mg l⁻¹ initial dye concentrations, the highest specific dye uptake measured was 41.29–41.17 mg g⁻¹ for Remazol Blue and 47.69–43.82 mg g⁻¹ for Reactive Black B at 45 °C and 50 °C incubation temperatures, respectively, after 8 days incubation.     

Decolorization of synthetic and real textile wastewater by the use of white-rot fungi

Batch and continuous reactors inoculated with white-rot fungi were operated in order to study decolorization of textile dyes. Synthetic wastewater containing either Reactive Blue 4 (a blue anthraquinone dye) or Reactive Red 2 (a red azo dye) was used during the first part of the study while real wastewater from a textile industry in Tanzania was used in the later part. Trametes versicolor was shown to decolorize both Reactive Blue 4 and Reactive Red 2 if glucose was added as a carbon source. Reactive Blue 4 was also decolorized when the fungus was allowed to grow on birch wood discs in a continuous biological rotating contactor reactor. The absorbance at 595 nm, the wavelength at which the dye absorbs at a maximum, decreased by 70% during treatment. The initial dye concentration in the medium was 200 mg/l and the hydraulic retention time in the reactor 3 days. No glucose was added in this experiment. Changes of the absorbance in the UV range indicated that the aromatic structures of the dyes were altered. Real textile wastewater was decolorized by Pleurotus flabellatus growing on luffa sponge packed in a continuous reactor. The reactor was operated at a hydraulic retention time of 25 h. The absorbance at 584 nm, the wavelength at which the wastewater absorbed the most, decreased from 0.3 in the inlet to approximately 0.1 in the effluent from the reactor.     

Decolorization of azo dye by immobilized Pseudomonas luteola entrapped in alginate–silicate sol–gel beads

Pseudomonas luteola was immobilized by entrapment in alginate–silicate sol–gel beads for decolorization of the azo dye, Reactive Red 22. The influences of biomass loading and operating conditions on specific decolorization rate and dye removal efficiency were studied in details. The immobilized cells were found to be less sensitive to changes in agitation rates (dissolved oxygen levels) and pH values. Michaelis–Menten kinetics could be used to describe the decolorization kinetics with the kinetic parameters being 36.5 mg g⁻¹ h⁻¹, 300.1 mg l⁻¹ and 18.2 mg g⁻¹ h⁻¹, 449.8 mg l⁻¹ for free and immobilized cells, respectively. After five repeated batch cycles, the decolorization rate of the free cells decreased by nearly 54%, while immobilized cells still retained 82% of their original activity. The immobilized cells exhibited better thermal stability during storage and reaction when compared with free cells. From SEM observation, a dense silicate gel layer was found to surround the macroporous alginate–silicate core, which resulted in much improved mechanical stability over that of alginate beads when tested under shaking conditions. Alginate–silicate matrices appeared to be the best matrix for immobilization of P. luteola in decolorization of Reactive Red 22 when compared with previous results using synthetic or natural polymer matrices.     

Decolorization of diazo dye Direct Red 81 by a novel bacterial consortium

Summary Samples collected from various effluent-contaminated soils in the vicinities of dyestuff manufacturing units of Ahmedabad, India, were studied for screening and isolation of organisms capable of decolorizing textile dyes. A novel bacterial consortium was selected on the basis of rapid decolorization of Direct Red 81 (DR 81), which was used as model dye. The bacterial consortium exhibited 90% decolorization ability within 35 h. Maximum rate of decolorization was observed when starch (0.6 g l⁻¹) and casein (0.9 g l⁻¹) were supplemented in the medium. Decolorization of DR 81 was monitored by high performance thin layer chromatography, which indicated that dye decolorization was due to its degradation into unidentified intermediates. The optimum dye-decolorizing activity of the culture was observed at pH 7.0 and incubation temperature of 37 °C. Maximum dye-decolorizing efficiency was observed at 200 mg l⁻¹ concentration of DR 81. The bacterial consortium had an ability to decolorize nine other structurally different azo dyes.     

Treatment of dye (Remazol Blue) and heavy metals using yeast cells with the purpose of managing polluted textile wastewaters

The bioaccumulation of chromium(VI), nickel(II), copper(II), and reactive dye by the yeast Rhodotorula mucilaginosa has been investigated in media containing molasses as a carbon and energy source. Optimal pH values for the yeast cells to remove the pollutants were pH 4 for copper(II) and dye, pH 6 for chromium(VI) and dye, and pH 5 for nickel(II) and dye in media containing 50 mg l^?1 heavy metal and 50 mg l^?1 Remazol Blue. The maximum dye bioaccumulation was observed within 4–6 days and uptake yields varied from 93% to 97%. The highest copper(II) removal yields measured were 30.6% for 45.4 mg l^?1 and 32.4% for 95.9 mg l^?1 initial copper(II) concentrations. The nickel(II) removal yield was 45.5% for 22.3 mg l^?1, 38.0% for 34.7 mg l^?1, and 30.3% for 62.2 mg l^?1. Higher chromium(VI) removal yields were obtained, such as 94.5% for 49.2 mg l^?1 and 87.7% for 129.2 mg l^?1 initial chromium(VI) concentration. The maximum dye and heavy metal bioaccumulation yield was investigated in media with a constant dye (approximately 50 mg l^?1) and increasing heavy metal concentration. In the medium with 48.9–98.8 mg l^?1 copper(II) and constant dye concentration, the maximum copper(II) bioaccumulation was 27.7% and 27.9% whereas the maximum dye bioaccumulation was 96.1% and 95.3%. The maximum chromium(VI) bioaccumulation in the medium with dye was 95.2% and 80.3% at 48.2 and 102.2 mg l^?1 chromium(VI) concentrations. In these media dye bioaccumulation was 76.1% and 35.1%, respectively. The highest nickel(II) removal was 6.1%, 20.3% and 16.0% in the medium with 23.8 mg l^?1 nickel(II) + 37.8 mg l^?1 dye, 38.1 mg l^?1 nickel(II) + 33.4 mg l^?1 dye and 59.0 mg l^?1 nickel(II) + 39.2 mg l^?1 dye, respectively. The maximum dye bioaccumulation yield in the media with nickel(II) was 94.1%, 78.0% and 58.7%, respectively.     

Accelerated decolorization of reactive azo dyes under saline conditions by bacteria isolated from Arabian seawater sediment

Presence of huge amount of salts in the wastewater of textile dyeing industry is one of the major limiting factors in the development of an effective biotreatment system for the removal of azo dyes from textile effluents. Bacterial spp. capable of thriving under high salt conditions could be employed for the treatment of saline dye-contaminated textile wastewaters. The present study was aimed at isolating the most efficient bacterial strains capable of decolorizing azo dyes under high saline conditions. Fifty-eight bacterial strains were isolated from seawater, seawater sediment, and saline soil, using mineral salt medium enriched with 100?mg?l^?1 Reactive Black-5 azo dye and 50?g NaCl l^?1 salt concentration. Bacterial strains KS23 (Psychrobacter alimentarius) and KS26 (Staphylococcus equorum) isolated from seawater sediment were able to decolorize three reactive dyes including Reactive Black 5, Reactive Golden Ovifix, and Reactive Blue BRS very efficiently in liquid medium over a wide range of salt concentration (0–100?g NaCl l^?1). Time required for complete decolorization of 100?mg dye l^?1 varied with the type of dye and salt concentration. In general, there was an inverse linear relationship between the velocity of the decolorization reaction (V) and salt concentration. This study suggested that bacteria isolated from saline conditions such as seawater sediment could be used in designing a bioreactor for the treatment of textile effluent containing high concentration of salts.     

White-rot fungus <Emphasis Type="Italic">Ganoderma</Emphasis> sp.En3 had a strong ability to decolorize and tolerate the anthraquinone,indigo and triphenylmethane dye with high concentrations

The ability of the white-rot fungus Ganoderma sp.En3 to decolorize different kinds of dyes widely applied in the textile and dyeing industry, including the anthraquinone dye Remazol Brilliant Blue R (RBBR), indigo dye indigo carmine and triphenylmethane dye methyl green, was evaluated in this study. Ganoderma sp.En3 had a strong capability of decolorizing high concentrations of RBBR, indigo carmine and methyl green. Obvious reduction of Chemical Oxygen Demand was observed after decolorization of different dyes. Ganoderma sp.En3 had a strong ability to tolerate RBBR, indigo carmine and methyl green with high concentrations. High concentrations of RBBR, indigo carmine and methyl green could also be efficiently decolorized by the crude enzyme of Ganoderma sp.En3. Different redox mediators such as syringaldehyde, acetosyringone and acetovanillone could enhance the decolorization capability for higher concentration of indigo carmine and methyl green. Different metal ions had little effect on the ability of the crude enzyme to decolorize indigo carmine and methyl green. Our study suggested that Ganoderma sp.En3 had a strong capability for decolorizing and tolerating high concentrations of different types of dyes such as RBBR, indigo carmine and methyl green.     

Decolorization and biodegradation of triphenylmethane dye,brilliant green,by Aspergillus sp. isolated from Ladakh,India

Brilliant green, used extensively to color silk and wool in the commercial textile industry is a hazardous recalcitrant. Aspergillus sp. strain CB-TKL-1 isolated from a water sample from Tsumoriri Lake, Karzok, Ladakh, India, was found to completely decolorize this dye within 72 h when cultured under aerobic conditions at 25 °C. The extent of decolorization was monitored by the decrease in absorbance maxima of the dye by UV–visible spectroscopy. The decolorization was optimum at pH 5 and 35 °C when agitated at 200 rpm. Addition of glucose (2%) as a carbon source and sodium nitrate (0.2%) as a nitrogen source enhanced the decolorization ability of the culture. The culture exhibited maximum extent of decolorization of brilliant green with a C:N ratio of 2.5 after 72 h. Thirteen N-demethylated decolorized products of brilliant green were identified based on UV–visible spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy and liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS) analysis at the end of 72 h before mineralization. The difference of the relative absorption peaks in the decolorized sample indicated a linear release of N-demethylated compounds, indicating a stepwise N-demethylation in the decolorization process.     

Characterization of a laccase gene from the white-rot fungi Trametes sp. 5930 isolated from Shennongjia Nature Reserve in China and studying on the capability of decolorization of different synthetic dyes

Laccase belongs to a family of multi-copper oxidases which is especially useful for biotechnological and industrial applications. A laccase-producing white-rot fungi strain designated as Trametes sp. 5930 was nearly isolated from Shennongjia Nature Reserve in China. Trametes sp. 5930 had the high yield of laccase and was capable of decolorizing different dyes efficiently. Laccase played a very important role in the decolorization of different dyes by this fungus. The laccase gene lac5930-1 and its corresponding full-length cDNA were then cloned and characterized from Trametes sp. 5930. The 1563 bp full-length cDNA of lac5930-1 encoded a mature laccase protein consisting of 499 amino acids preceded by a signal peptide of 21 amino acids. lac5930-1 gene was successfully expressed in Pichia pastoris, which verified the function of lac5930-1 encoding active laccase by means of gene expression. The recombinant laccase produced by the yeast transformant in which lac5930-1 was efficiently expressed, conferred the ability to decolorize different dyes. The capability of decolorizing different dyes was positively related to the laccase activity, which provided strong evidence for the important function of laccase used in decolorizing industrial dyes.     

Decolorization of Reactive Red 195 by a mixed culture in an alternating anaerobic–aerobic Sequencing Batch Reactor

The mono-azo dye Reactive Red 195 (RR 195) is a widely used color compound in the textile industry. As many other colors, it is persistent and difficult to be removed from water with conventional processes. The present study investigates biological decolorization of RR 195 under alternate anaerobic–aerobic conditions in a laboratory scale Sequencing Batch Reactor (SBR) containing a mixed culture and fed with a biodegradable carbon source. Different values of the Sludge Retention Time (SRT), Hydraulic Retention Time (HRT), influent color and organic carbon loadings were adopted during the experimental activity and their effects on color and Chemical Oxygen Demand (COD) removal efficiencies and process kinetics determined. The optimal operating conditions were found to be: 800 mg l⁻¹ influent COD, 50 d SRT and a 24 h-cycle. Under these conditions, the maximum color efficiency of 97% was achieved for a 40 mg l⁻¹ RR 195 in the feed. Some inhibition was present at influent color loadings above 40 mg l⁻¹, which was confirmed by the application of the Haldane model.     

Bioinformatics aided microbial approach for bioremediation of wastewater containing textile dyes

Four textile azo dyes, Joyfix Red, Remazol Red, Reactive Red and Reactive Yellow, were studied for decolorization. Of nineteen soil bacterial isolates, two novel strains were found to highly decolorize Joyfix Red and were identified as Lysinibacillus sphaericus (KF032717) and Aeromonas hydrophila (KF032718) through 16S rDNA analysis. Laccase and Azoreductase enzyme modeling and enzyme–dye interaction performed using Schrödinger Suite imitated decolorization percentage. Results based on cumulative Glide score (Dry laboratory) and decolorization percentage of the other three dyes based on ultraviolet–visible (UV–vis) spectroscopy (Wet laboratory) were reliable. Biodegradation of Joyfix Red was confirmed by high-performance liquid chromatography (HPTLC) elution profile which showed four peaks at 1.522, 1.800, 3.068 and 3.804 min with that of parent dye which showed single peak at 1.472 min. Fourier transform infrared spectroscopy (FT-IR) analysis supported the biotransformation of Joyfix Red. Gas chromatography–mass spectroscopy (GC–MS) analysis showed sodium (3E,5Z)-4-amino-6-hydroxyhexa-13,5-triene-2-sulfonate was formed as end product during biodegradation. From these findings, it can be inferred that enzyme and dye interaction studies can assist in examining decolorization efficiency of bacteria and its enzyme, thereby enhancing the bioremediation process by reducing preliminary lengthy wet laboratory screening. This is the first report of a combinatorial in silico cum in vitro approach and its validation for the bioremediation of wastewater containing these textile azo dyes.     

Characterization of a salt resistant bacterial strain <Emphasis Type="Italic">Proteus</Emphasis> sp. NA6 capable of decolorizing reactive dyes in presence of multi-metal stress

Microbial biotechnologies for the decolorization of textile wastewaters have attracted worldwide attention because of their economic suitability and easiness in handling. However, the presence of high amounts of salts and metal ions in textile wastewaters adversely affects the decolorization efficiency of the microbial bioresources. In this regard, the present study was conducted to isolate salt tolerant bacterial strains which might have the potential to decolorize azo dyes even in the presence of multi-metal ion mixtures. Out of the tested 48 bacteria that were isolated from an effluent drain, the strain NA6 was found relatively more efficient in decolorizing the reactive yellow-2 (RY2) dye in the presence of 50 g L^?1 NaCl. Based on the similarity of its 16S rRNA gene sequence and its position in a phylogenetic tree, this strain was designated as Proteus sp. NA6. The strain NA6 showed efficient decolorization (>90 %) of RY2 at pH 7.5 in the presence of 50 g L^?1 NaCl under static incubation at 30 °C. This strain also had the potential to efficiently decolorize other structurally related azo dyes in the presence of 50 g L^?1 NaCl. Moreover, Proteus sp. NA6 was found to resist the presence of different metal ions (Co⁺², Cr⁺⁶, Zn⁺², Pb⁺², Cu⁺², Cd⁺²) and was capable of decolorizing reactive dyes in the presence of different levels of the mixtures of these metal ions along with 50 g L^?1 NaCl. Based on the findings of this study, it can be suggested that Proteus sp. NA6 might serve as a potential bioresource for the biotechnologies involving bioremediation of textile wastewaters containing the metal ions and salts.     

Characterization of a laccase-like multicopper oxidase from newly isolated Streptomyces sp. C1 in agricultural waste compost and enzymatic decolorization of azo dyes

Laccases or laccase-like multicopper oxidases (LMCOs) could catalyze the oxidation of various substrates coupled to the reduction of oxygen to water. In this study, eight strains with laccase activity were isolated from composting samples in different phases, among which strain C1 isolated from the thermophilic-phase sample presented the highest laccase activity. The purified LMCO of strain C1 showed a single protein band on SDS-PAGE gel with a molecular mass of about 38 kDa. The novel laccase showed alkaline resistance and moderate thermostability. The enzyme activity was activated by some metal ions such as Cu²⁺, Co²⁺ and Fe³⁺ at the concentration of 1 mM, while was strongly inhibited in the presence of Hg²⁺. The LMCO could efficiently decolorize the indigo carmine and diamond black PV with syringaldehyde as mediator, which suggested a great potential for dye decolorization in the textile industry. The novel strain was identified as Streptomyces sp. C1. The finding of new laccase-producing Streptomyces sp. C1 in this study will also contribute to the further explanation of the function of Actinomycetes in the thermophilic phase of composting.     

Predictive expressions of growth and Remazol Turquoise Blue-G reactive dye bioaccumulation properties of Candida utilis

The combined effects of initial sucrose and initial Remazol Turquoise Blue-G (RTBG) reactive dye concentrations on the specific growth rate and dye bioaccumulation efficiency of Candida utilis was investigated and optimized using response surface methodology (RSM) in this study. A 2² full factorial central composite design was successfully used for experimental design and analyses of the results. Two numerical correlations fitted to a second-order quadratic equation were obtained to estimate the responses of specific growth rate and dye uptake yield. The statistical analysis indicated that both the microbial growth and removal yield of dye enhanced with raising sucrose concentration up to 15 g l^?1 and diminished with the increase in initial RTBG dye concentration up to approximately 500 mg l^?1 due to inhibition caused by high concentrations of RTBG dye. The optimum combination predicted via RSM confirmed that C. utilis was capable of bioaccumulating RTBG with the maximum uptake yield of 82.0% in 15 g l^?1 sucrose and 50 mg l^?1 dye containing growth medium.     

Isolation and characterization of a lead (Pb) tolerant <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> strain HF5 for decolorization of reactive red-120 and other azo dyes

Presence of heavy metals including lead (Pb) in the textile effluents is a crucial factor affecting the growth and potential of the dye decolorizing bacterial strains. This work was planned to isolate and characterize a bacterial strain exhibiting the potential to decolorize a range of azo dyes as well as the resistance to Pb. In this study, several Pb tolerant bacteria were isolated from effluents of textile industry. These bacterial isolates were screened for their potential of decolorizing the reactive red-120 (RR120) azo dye with presence of Pb (50 mg L^?1). The most efficient isolate was further characterized for its potential to resist Pb and decolorize different azo dyes under varying cultural and incubation conditions. Out of the total 82 tested bacterial isolates, 30 bacteria were found to have varying potentials to resist the presence of lead (Pb) and carry out decolorization of an azo dye reactive red-120 (RR120) in the medium amended with Pb (50 mg L^?1). The most efficient selected bacterium, Pseudomonas aeruginosa strain HF5, was found to show a good potential not only to grow in the presence of considerable concentration of Pb but also to decolorize RR120 and other azo dyes in the media amended with Pb. The strain HF5 completely (>?90%) decolorized RR120 in mineral salt medium amended with 100 mg L^?1 of Pb and 20 g L^?1 NaCl. This strain also considerably (>?50%) decolorized RR120 up to the presence of 2000 mg L^?1 of Pb and 50 g L^?1 of NaCl but with reduced rate. The optimal decolorization of RR120 by HF5 was achieved when the pH of the Pb amended (100 mg L^?1) mineral salt media was adjusted at 7.5 and 8.5. Interestingly, this strain also showed the tolerance to a range of metal ions with varying MIC values. The Pseudomonas aeruginosa strain HF5 harboring the unique potentials to grow and decolorize the azo dyes in the presence of Pb is envisaged as a potential bioresource for devising the remediation strategies for treatment of colored textile wastewaters loaded with Pb and other heavy metal ions.     

Biodegradation of reactive textile dye Red BLI by an isolated bacterium Pseudomonas sp. SUK1

A novel bacterial strain capable of decolorizing reactive textile dye Red BLI is isolated from the soil sample collected from contaminated sites of textile industry from Solapur, India. The bacterial isolate was identified as Pseudomonas sp. SUK1 on the basis of 16S rDNA analysis. The Pseudomonas sp. SUK1 decolorized Red BLI (50 mg l(-1)) 99.28% within 1h under static anoxic condition at pH range from 6.5 to 7.0 and 30 degrees C. This strain has ability to decolorize various reactive textile dyes. UV-Vis spectroscopy, FTIR and TLC analysis of samples before and after dye decolorization in culture medium confirmed decolorization of Red BLI. A significant increase in the activities of aminopyrine N-demethylase and NADH-DCIP reductase in cells obtained after decolorization indicates involvement of these enzymes in the decolorization process. Phytotoxicity testing with the seeds of Sorghum vulgare and Phaseolus mungo, showed more sensitivity towards the dye, while the products obtained after dye decolorization does not have any inhibitory effects.     

Purification and characterization of an azoreductase from Escherichia coli CD-2 possessing quinone reductase activity

An oxygen-insensitive intracellular enzyme that is responsible for the decolorization of azo dyes was purified from Escherichia coli CD-2. The molecular weight of the purified enzyme was estimated as 27,000 ± 500 Da. Protein identification indicated that the enzyme had high sequence homology with E. coli K12 quinone reductase, and the enzyme was proved to have both azoreductase and quinone reductase activity. With methyl red as substrate, the optimal pH value and temperature were 6.5 and 37 °C, respectively. The enzyme was stable under different physiochemical conditions. The azoreductase activity was restrained by SDS and was almost completely inhibited by Co²⁺ and Hg²⁺. K_m and V_max values were 0.18 mM and 8.12 U mg^?1 of protein for NADH and 0.05 mM and 6.46 U mg^?1 of protein for methyl red, respectively. The purified enzyme could efficiently decolorize methyl red with both NADH and NADPH as electron donors.