Biodegradation perspectives of azo dyes by yeasts

Azo dyes are the largest class of synthetic dyes, which are widely used in the textile industry. The amount of dyestuff does not bind to the fibers and is lost in wastewater during textile processing. The discharge of colored effluents into the environment is not only aesthetically unpleasing. Moreover, dyes and their break-down products cause toxic effects and they affect photosynthetic activity of aquatic systems by reducing light penetration. A number of microorganisms belonging to different taxonomic groups of bacteria, algae, fungi and yeast have been reported for their ability to decolorize azo dyes. In the literature the ability to decolorize azo dyes by yeasts, compared to bacterial and fungal species, has been studied in a few reports. Within this review, an attempt is made to elucidate some basic biological aspects associated with the azo dye degradation by yeasts and enzymes involved that are responsible for degradation process.     

Reduction of azo dyes by anaerobic bacteria: microbiological and biochemical aspects

Azo dyes are recalcitrant pollutants commonly found in several industrial wastewaters, such as those originated from textile factories, which generally persist to biological transformation. Discharge of these effluents in open water bodies not only represents an aesthetic problem, but also may limit photosynthesis in aquatic plants. Furthermore, many azo dyes and products derived from their partial transformation in the environment (e.g. aromatic amines) may be toxic or carcinogenic. Biological wastewater treatment processes have emerged as promising technologies to remove azo dyes from industrial effluents and intensive research has been conducted during the last two decades in order to elucidate the mechanisms involved in the reductive decolourisation of azo dyes. The present work describes the main biochemical and microbiological aspects involved in the reductive decolourisation of azo dyes by anaerobic bacteria.     

Bacterial decolorization and degradation of azo dyes

Azo compounds constitute the largest and the most diverse group of synthetic dyes and are widely used in a number of industries such as textile, food, cosmetics and paper printing. They are generally recalcitrant to biodegradation due to their xenobiotic nature. However microorganisms, being highly versatile, have developed enzyme systems for the decolorization and mineralization of azo dyes under certain environmental conditions. Several genera of Basidomycetes have been shown to mineralize azo dyes. Reductive cleavage of azo bond, leading to the formation of aromatic amines, is the initial reaction during the bacterial metabolism of azo dyes. Anaerobic/anoxic azo dye decolorization by several mixed and pure bacterial cultures have been reported. Under these conditions, this reaction is non-specific with respect to organisms as well as dyes. Various mechanisms, which include enzymatic as well as low molecular weight redox mediators, have been proposed for this non-specific reductive cleavage. Only few aerobic bacterial strains that can utilize azo dyes as growth substrates have been isolated. These organisms generally have a narrow substrate range. Degradation of aromatic amines depends on their chemical structure and the conditions. It is now known that simple aromatic amines can be mineralized under methanogenic conditions. Sulfonated aromatic amines, on the other hand, are resistant and require specialized aerobic microbial consortia for their mineralization. This review is focused on the bacterial decolorization of azo dyes and mineralization of aromatic amines, as well as the application of these processes for the treatment of azo-dye-containing wastewaters.     

Basic and applied aspects in the microbial degradation of azo dyes

Azo dyes are the most important group of synthetic colorants. They are generally considered as xenobiotic compounds that are very recalcitrant against biodegradative processes. Nevertheless, during the last few years it has been demonstrated that several microorganisms are able, under certain environmental conditions, to transform azo dyes to non-colored products or even to completely mineralize them. Thus, various lignolytic fungi were shown to decolorize azo dyes using ligninases, manganese peroxidases or laccases. For some model dyes, the degradative pathways have been investigated and a true mineralization to carbon dioxide has been shown. The bacterial metabolism of azo dyes is initiated in most cases by a reductive cleavage of the azo bond, which results in the formation of (usually colorless) amines. These reductive processes have been described for some aerobic bacteria, which can grow with (rather simple) azo compounds. These specifically adapted microorganisms synthesize true azoreductases, which reductively cleave the azo group in the presence of molecular oxygen. Much more common is the reductive cleavage of azo dyes under anaerobic conditions. These reactions usually occur with rather low specific activities but are extremely unspecific with regard to the organisms involved and the dyes converted. In these unspecific anaerobic processes, low-molecular weight redox mediators (e.g. flavins or quinones) which are enzymatically reduced by the cells (or chemically by bulk reductants in the environment) are very often involved. These reduced mediator compounds reduce the azo group in a purely chemical reaction. The (sulfonated) amines that are formed in the course of these reactions may be degraded aerobically. Therefore, several (laboratory-scale) continuous anaerobic/aerobic processes for the treatment of wastewaters containing azo dyes have recently been described.     

Microbial decolouration of azo dyes: A review

The textile industry is a substantial consumer of water and produces enormous volumes of contaminated water; the most important contaminants are azo dyes. Microbial processes for the treatment of textile wastewater have the advantage of being cost-effective and environmentally friendly and producing less sludge. The most promising microorganisms for wastewater treatment are those isolated from sites contaminated with dyes or from the sludge of treatment plants because they have adapted to survive in adverse conditions. The mechanism of microbial decolouration occurs from adsorption, enzymatic degradation or a combination of both. Both reductases and oxidases are involved in the microbial degradation process. The goal of microbial treatment is to decolourise and detoxify the dye-contaminated effluents. In this review, we summarise the methodologies used to evaluate the toxicity of azo dyes and their degradation products. Recent studies on the decolouration or degradation of azo dyes using algae, yeast, filamentous fungi and bacteria, genetically modified microorganisms, microbial consortia and microbiological systems combined with Advanced Oxidation Processes (AOPs) and Microbial Fuel Cells (MFCs) are discussed in this review.     

微生物在水环境污染物降解中的应用

每年有大量来自工业、农业、养殖业和城市污水处理厂的废水被排入到水环境中, 因此, 地球上的水环境面临大量来自生活废水、工农业废水、非法排放的废水及其它废水的污染物质(如抗生素、杀虫剂、除草剂、烃等)的严重挑战, 特别是近年来随着集约化养殖的发展, 废水污染问题日益突出, 并且随着分析手段的进步, 能够检测到被排入水环境中的化学污染物质也越来越多, 这些化学污染物对水环境中的生物产生有害影响。但是, 微生物在污染控制上具有许多重要的作用。因此, 本文对微生物在水环境污染物降解中的应用进行了评论。结果表明微生物主要是应用在水产养殖水中, 而在其它的水体系(如河、湖、海)的应用较少。     

微生物在水环境污染物降解中的应用

每年有大量来自工业、农业、养殖业和城市污水处理厂的废水被排入到水环境中,因此,地球上的水环境面临大量来自生活废水、工农业废水、非法排放的废水及其它废水的污染物质(如抗生素、杀虫剂,除草剂、烃等)的严重挑战,特别是近年来随着集约化养殖的发展,废水污染问题日益突出,并且随着分析手段的进步,能够检测到被排入水环境中的化学污染物质也越来越多,这些化学污染物对水环境中的生物产生有害影响.但是,微生物在污染控制上具有许多重要的作用.因此,本文对微生物在水环境污染物降解中的应用进行了评论.结果表明微生物主要是应用在水产养殖水中,而在其它的水体系(如河、湖、海)的应用较少.     

微生物在水环境污染物降解中的应用（英文稿）

每年有大量来自工业、农业、养殖业和城市污水处理厂的废水被排入到水环境中, 因此, 地球上的水环境面临大量来自生活废水、工农业废水、非法排放的废水及其它废水的污染物质(如抗生素、杀虫剂、除草剂、烃等)的严重挑战, 特别是近年来随着集约化养殖的发展, 废水污染问题日益突出, 并且随着分析手段的进步, 能够检测到被排入水环境中的化学污染物质也越来越多, 这些化学污染物对水环境中的生物产生有害影响。但是, 微生物在污染控制上具有许多重要的作用。因此, 本文对微生物在水环境污染物降解中的应用进行了评论。结果表明微生物主要是应用在水产养殖水中, 而在其它的水体系(如河、湖、海)的应用较少。     

Azo dyes degradation by microorganisms – An efficient and sustainable approach

Synthetic aromatic compounds consisting of various functional groups are known as dyes. These colored compounds are often discharged in effluents, and they are very dangerous to aquatic life. Basically, the dye industry started by using natural plant and insect sources, and then suddenly turned into artificial manufacturing. Natural equilibrium of our environment gets changed by the reduction in photosynthetic activity due to the dyes. In China 900,000 tons of all kinds of dyes are usually produced, which are used in many industries like food, textile, food, paper and leather. Untreated wastewater contaminates aquatic bodies by causing eutrophication, change in water color, oxygen depletion which affect aquatic organisms to a great extent. Dye wastewater is now the key environmental pollution form. In recent eras an extensive study line has been developed to explore the dye decolorization and biodegradation under both aerobic as well as anaerobic conditions. In this review, the chemistry, toxicity and microbial biodegradation/decolorization are presented. Some recent studies along with the new techniques and methodologies of remediating the dye pollution are also discussed to provide the bases of their handling. Overall, efficient and high biodegradation potential make microbes an impending foundation for green chemistry to eradicate toxic dyes from industrial wastewater.     

Evaluation of the Presence of Mutagenic Dyes in Sediments from Cristais River

Azo dyes are largely used by coloring textiles and can contaminate the aquatic environment, including the sediment, through their release through effluent discharges. In this work the presence of mutagenic azo dyes was evaluated using Thin Layer Chromatography in sediment samples of the Cristais River upstream and downstream of an azo dye processing plant discharge area. Mutagenicity of the sediment samples was also analyzed using the Salmonella/microsome assay with the strain YG1041 in the presence and absence of S9. Extracts of benthic organisms collected in the same area were analyzed for the presence of dyes. The dyes CI Disperse Blue 373 and CI Disperse Orange 37 as well as three unknown fluorescent compounds were detected only in the sediment samples collected downstream of the industrial discharge. Activity was detected with the Salmonella assay in the three samples analyzed but higher values were obtained after the azo dye processing plant when compared to the reference site. This effect could be partially explained by the presence of the mutagenic dyes detected, considering their mutagenic potencies. No dyes were found in the extracts of the organisms. Further studies should be performed to evaluate the fate and effects of these dyes in the sediment and in the aquatic community and their potential to be transferred to the water column.     

微生物对偶氮染料的脱色及其基因工程研究进展

偶氮染料广泛应用在纺织印染、造纸印刷等行业中。染料废水的排放将会导致严重的环境污染,使用微生物处理染料废水是解决此问题的有效方法。该文概述了微生物对偶氮染料的脱色的研究,包括细菌对偶氮染料的脱色,真菌对偶氮染料的脱色,脱色产生的芳香胺并进一步被降解,以及基因工程技术在微生物对偶氮染料脱色的研究进展。     

Effectiveness of Rice Agricultural Waste,Microbes and Wetland Plants in the Removal of Reactive Black-5 Azo Dye in Microcosm Constructed Wetlands

Azo dyes are commonly generated as effluent pollutants by dye using industries, causing contamination of surface and ground water. Various strategies are employed to treat such wastewater; however, a multi-faceted treatment strategy could be more effective for complete removal of azo dyes from industrial effluent than any single treatment. In the present study, rice husk material was used as a substratum in two constructed wetlands (CWs) and augmented with microorganisms in the presence of wetland plants to effectively treat dye-polluted water. To evaluate the efficiency of each process the study was divided into three levels, i.e., adsorption of dye onto the substratum, phytoremediation within the CW and then bioremediation along with the previous two processes in the augmented CW. The adsorption process was helpful in removing 50% dye in presence of rice husk while 80% in presence of rice husk biocahr. Augmentation of microorganisms in CW systems has improved dye removal efficiency to 90%. Similarly presence of microorganisms enhanced removal of total nitrogen (68% 0 and Total phosphorus (75%). A significant improvement in plant growth was also observed by measuring plant height, number of leaves and leave area. These findings suggest the use of agricultural waste as part of a CW substratum can provide enhanced removal of textile dyes.     

几种氯苯对模拟氧化塘系统生物群落的影响

研究一氯苯,１,２,３－三氯苯及六氯苯对模拟氧化塘系统生物群落结构的影响及其净化机制。结果表明,在５．６０９５ｍｇ／ｌ的一氯苯,１．９２９２ｍｇ／ｌ的１,２,３－三氯苯及０．１３６３ｍｇ／ｌ的六氯苯实验条件下,系统中杆菌属、微球菌属及酵母菌属的种类、密度影响不明显;对浮游藻类的种、数量及叶绿素ａ的合成有明显地抑制作用,其影响大小的顺序为：六氯苯〉１,２,３－三氯苯〉一氯苯。在模拟氧化塘系统中,氯苯     

Special traits of decomposition of azo dyes by anaerobic microbial communities

We present the results of an investigation into the special traits of conversion of azo dyes Acid Orange 6, Acid Orange 7, Methyl Orange, and Methyl Red under anaerobic conditions in comparison to aerobic conditions. In the presence of oxygen, only Methyl Red underwent decomposition, while under oxygen-free conditions, all remaining substances were fully decolourised under the action of a methanogenous consortium of microorganisms. The products of reduction of the azo bond are determined in the case of each dye. Introduction of additional acceptors of electrons (sulfate and nitrate) had a negative influence on the discoloration of azo dyes. Addition of ethanol as an available organic cosubstrate accelerated decomposition of azo dyes both under methanogenous and sulfate- and nitrate-reducing conditions. There is no direct correlation between the rates of conversion of azo dyes under anaerobic conditions or their toxicity to acetoclastic methanogens. Changes in the morphological composition of the community decolouring an azo dye depended on the duration of its impact on microorganisms. The mechanism of the reduction of the azo bond under the action of substances acting as mediators is explained. These substances are products of the metabolism of the microbial community in anaerobic conditions. It is shown that the supposed mediators NADH and sulfide efficiently decolourise azo dyes in a cell-free system, while riboflavin significantly increased the rate of conversion of substrates in recurrent cycles of discoloration only in the presence of an anaerobic microbial consortium.     

Mineralization of sulfonated azo dyes and sulfanilic acid by Phanerochaete chrysosporium and Streptomyces chromofuscus.

Five 14C-radiolabeled azo dyes and sulfanilic acid were synthesized and used to examine the relationship between dye substitution patterns and biodegradability (mineralization to CO2) by a white-rot fungus and an actinomycete. 4-Amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid were used as representative compounds having sulfo groups or both sulfo and azo groups. Such compounds are not known to be present in the biosphere as natural products. The introduction of lignin-like fragments into the molecules of 4-amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid by coupling reactions with guaiacol (2-methoxyphenol) resulted in the formation of the dyes 4-(3-methoxy-4-hydroxyphenylazo)-[U-14C]benzenesulfonic acid and 4-(2-sulfo-3'-methoxy-4'-hydroxy-azobenzene-4-azo)-[U-14C]benzenesulf oni c acid, respectively. The synthesis of acid azo dyes 4-(2-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid and 4-(4-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid also allowed the abilities of these microorganisms to mineralize these commercially important compounds to be evaluated. Phanerochaete chrysosporium mineralized all of the sulfonated azo dyes, and the substitution pattern did not significantly influence the susceptibility of the dyes to degradation. In contrast, Streptomyces chromofuscus was unable to mineralize aromatics with sulfo groups and both sulfo and azo groups. However, it mediated the mineralization of modified dyes containing lignin-like substitution patterns. This work showed that lignocellulolytic fungi and bacteria can be used for the biodegradation of anionic azo dyes, which thus far have been considered among the xenobiotic compounds most resistant to biodegradation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mineralization of sulfonated azo dyes and sulfanilic acid by Phanerochaete chrysosporium and Streptomyces chromofuscus.

Five 14C-radiolabeled azo dyes and sulfanilic acid were synthesized and used to examine the relationship between dye substitution patterns and biodegradability (mineralization to CO2) by a white-rot fungus and an actinomycete. 4-Amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid were used as representative compounds having sulfo groups or both sulfo and azo groups. Such compounds are not known to be present in the biosphere as natural products. The introduction of lignin-like fragments into the molecules of 4-amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid by coupling reactions with guaiacol (2-methoxyphenol) resulted in the formation of the dyes 4-(3-methoxy-4-hydroxyphenylazo)-[U-14C]benzenesulfonic acid and 4-(2-sulfo-3'-methoxy-4'-hydroxy-azobenzene-4-azo)-[U-14C]benzenesulf oni c acid, respectively. The synthesis of acid azo dyes 4-(2-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid and 4-(4-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid also allowed the abilities of these microorganisms to mineralize these commercially important compounds to be evaluated. Phanerochaete chrysosporium mineralized all of the sulfonated azo dyes, and the substitution pattern did not significantly influence the susceptibility of the dyes to degradation. In contrast, Streptomyces chromofuscus was unable to mineralize aromatics with sulfo groups and both sulfo and azo groups. However, it mediated the mineralization of modified dyes containing lignin-like substitution patterns. This work showed that lignocellulolytic fungi and bacteria can be used for the biodegradation of anionic azo dyes, which thus far have been considered among the xenobiotic compounds most resistant to biodegradation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reaction mechanism of azoreductases suggests convergent evolution with quinone oxidoreductases

Azoreductases are involved in the bioremediation by bacteria of azo dyes found in waste water. In the gut flora, they activate azo pro-drugs, which are used for treatment of inflammatory bowel disease, releasing the active component 5-aminosalycilic acid. The bacterium P. aeruginosa has three azoreductase genes, paAzoR1, paAzoR2 and paAzoR3, which as recombinant enzymes have been shown to have different substrate specificities. The mechanism of azoreduction relies upon tautomerisation of the substrate to the hydrazone form. We report here the characterization of the P. aeruginosa azoreductase enzymes, including determining their thermostability, cofactor preference and kinetic constants against a range of their favoured substrates. The expression levels of these enzymes during growth of P. aeruginosa are altered by the presence of azo substrates. It is shown that enzymes that were originally described as azoreductases, are likely to act as NADH quinone oxidoreductases. The low sequence identities observed among NAD(P)H quinone oxidoreductase and azoreductase enzymes suggests convergent evolution.     

BiodEnz:A database of biodegrading enzymes

Azo dyes, which re characterized by azo bonds, are a predominant class of colorants used in tattooing, cosmetics, foods, textile and consumer products. Laccases (EC 1.10.3.2), lignin peroxidases (EC 1.11.1.14) , Azo reductases (EC 1.7.1.6) of different micro organisms are mainly useful for the development of biodegradation systems as they catalyse reductive cleavage of azo groups (-N=N-) . Laccases have very broad substrate specificity with respect to the electron donor and is capable of oxidizing phenols and aromatic amines. Azoreductase belongs to the family of oxidoreductases, acting on other nitrogenous compounds as donors with NAD+ or NADP+ as acceptor. Lignin peroxidase enzymes are highly non-specific and are well reported to decolourize various dyes We have developed BiodEnz database by collecting information like strains that produce particular enzymes, azo dyes that are degraded , substrate specificity, molecular weight, the optimum temperature and pH, sequence data of the above enzymes ,as the most effective inoculants used for bioremediation are able to degrade dyes over a broad concentration range, tolerate a range of environmental conditions of temperature, pH, and activity of the enzymes. The database can be searched by using a user friendly web interface. AVAILABILITY: The database is available for free at http://www.biodenzdatabase.in.     

Potential of aquatic fungi derived from diverse freshwater environments to decolourise synthetic azo and anthraquinone dyes

A total of 37 strains of aquatic hyphomycetes and 95 fungal isolates derived from diverse freshwater environments were screened on agar plates for the decolourisation of the disazo dye Reactive Black 5 and the anthraquinone dye Reactive Blue 19. The decolourisation of 9 azo and 3 anthraquinone dyes by 9 selected aquatic fungi was subsequently assessed in a liquid test system. The fungi were representatives of mitosporic anamorphs, and 6 strains had proven ascomycete affiliations. For comparison, 5 white rot basidiomycetes were included. The majority of dyes were decolourised by several mitosporic aquatic isolates at rates essentially comparable to those observed with the most efficient white rot fungus. Under certain conditions, particular aquatic strains decolourised dyes even more efficiently than the best performing white rot basidiomycete. Upon fungal treatment of several dyes, new absorbance peaks appeared, indicating biotransformation metabolites. All together, these results point to the potential of fungi occurring in freshwater environments for the treatment of dye-containing effluents.     

Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative

The control of water pollution has become of increasing importance in recent years. The release of dyes into the environment constitutes only a small proportion of water pollution, but dyes are visible in small quantities due to their brilliance. Tightening government legislation is forcing textile industries to treat their waste effluent to an increasingly high standard. Currently, removal of dyes from effluents is by physio-chemical means. Such methods are often very costly and although the dyes are removed, accumulation of concentrated sludge creates a disposal problem. There is a need to find alternative treatments that are effective in removing dyes from large volumes of effluents and are low in cost, such as biological or combination systems. This article reviews the current available technologies and suggests an effective, cheaper alternative for dye removal and decolourisation applicable on large scale.