Horseradish peroxidase-catalyzed oxidative coupling of 3-methyl 2-benzothiazolinone hydrazone and methoxyphenols

The reaction between o-, m-, and p-methoxyphenols and 3-methyl-2-benzothiazolinone hydrazone (MBTH) is studied in the presence of horseradish peroxidase (HRP) and H₂O₂ as oxidative agent. The findings indicate that enzyme (H₂O₂ oxidoreductase; EC 1.11.1.7) catalyzes an oxidative coupling reaction between MBTH and phenols which produces azo dye compounds. On the basis of kinetic parameters and optimum pH values, a mechanism in which both MBTH and phenols seem to be activated by the HRP for achieving the oxidative coupling is proposed. Furthermore, in the current study, we have evaluated the possibility that these azo dyes may be useful in the measurement of peroxidase activity. The method is based on the observed increase in the absorbance at 502 nm (8,355 cm^{−1 −1} of extinction molar coefficient) due to the formation of a red azo dye compound resulting from the peroxidase-catalyzed oxidative coupling of MBTH and o-methoxyphenol (guaiacol). Using this assay system, HRP can be determined in picomolar levels by a fixed time method.     

Influence of aromatic substitution patterns on azo dye degradability by Streptomyces spp. and Phanerochaete chrysosporium.

Twenty-two azo dyes were used to study the influence of substituents on azo dye biodegradability and to explore the possibility of enhancing the biodegradabilities of azo dyes without affecting their properties as dyes by changing their chemical structures. Streptomyces spp. and Phanerochaete chrysosporium were used in the study. None of the actinomycetes (Streptomyces rochei A10, Streptomyces chromofuscus A11, Streptomyces diastaticus A12, S. diastaticus A13, and S. rochei A14) degraded the commercially available Acid Yellow 9. Decolorization of monosulfonated mono azo dye derivatives of azobenzene by the Streptomyces spp. was observed with five azo dyes having the common structural pattern of a hydroxy group in the para position relative to the azo linkage and at least one methoxy and/or one alkyl group in an ortho position relative to the hydroxy group. The fungus P. chrysosporium attacked Acid Yellow 9 to some extent and extensively decolorized several azo dyes. A different pattern was seen for three mono azo dye derivatives of naphthol. Streptomyces spp. decolorized Orange I but not Acid Orange 12 or Orange II. P. chrysosporium, though able to transform these three azo dyes, decolorized Acid Orange 12 and Orange II more effectively than Orange I. A correlation was observed between the rate of decolorization of dyes by Streptomyces spp. and the rate of oxidative decolorization of dyes by a commercial preparation of horseradish peroxidase type II, extracellular peroxidase preparations of S. chromofuscus A11, or Mn(II) peroxidase from P. chrysosporium. Ligninase of P. chrysosporium showed a dye specificity different from that of the other oxidative enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of aromatic substitution patterns on azo dye degradability by Streptomyces spp. and Phanerochaete chrysosporium.

Twenty-two azo dyes were used to study the influence of substituents on azo dye biodegradability and to explore the possibility of enhancing the biodegradabilities of azo dyes without affecting their properties as dyes by changing their chemical structures. Streptomyces spp. and Phanerochaete chrysosporium were used in the study. None of the actinomycetes (Streptomyces rochei A10, Streptomyces chromofuscus A11, Streptomyces diastaticus A12, S. diastaticus A13, and S. rochei A14) degraded the commercially available Acid Yellow 9. Decolorization of monosulfonated mono azo dye derivatives of azobenzene by the Streptomyces spp. was observed with five azo dyes having the common structural pattern of a hydroxy group in the para position relative to the azo linkage and at least one methoxy and/or one alkyl group in an ortho position relative to the hydroxy group. The fungus P. chrysosporium attacked Acid Yellow 9 to some extent and extensively decolorized several azo dyes. A different pattern was seen for three mono azo dye derivatives of naphthol. Streptomyces spp. decolorized Orange I but not Acid Orange 12 or Orange II. P. chrysosporium, though able to transform these three azo dyes, decolorized Acid Orange 12 and Orange II more effectively than Orange I. A correlation was observed between the rate of decolorization of dyes by Streptomyces spp. and the rate of oxidative decolorization of dyes by a commercial preparation of horseradish peroxidase type II, extracellular peroxidase preparations of S. chromofuscus A11, or Mn(II) peroxidase from P. chrysosporium. Ligninase of P. chrysosporium showed a dye specificity different from that of the other oxidative enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

毛木耳对孔雀石绿染料降解条件的优化

随着我国印染工业的发展,废水对生态环境的危害日趋严重,亟需开发一种脱色明显且成本低廉的降解方法。本研究发现毛木耳Auricularia cornea菌株AC5对不同结构的染料均具有一定的降解作用,尤其是三苯甲烷类染料。利用26℃、160r/min振荡培养7d的粗酶液对染料（75.0mg/L）进行12h降解,结果显示三苯甲烷染料孔雀石绿、结晶紫,蒽醌染料活性蓝19和偶氮染料活性蓝222的降解效率分别为83.27%、71.77%、67.81%和63.92%。染料降解实验和酶活力测定结果表明,毛木耳对孔雀石绿的降解率达到最高时漆酶活性最高,为321.0U/mL,木质素过氧化物酶和锰过氧化物酶活性较低。因此,推测在降解过程中漆酶起到主要作用。研究表明利用毛木耳菌丝发酵液降解染料废水成本低且操作方便,为染料废水的降解研究提供了前期基础。     

Degradation of azo compounds by ligninase from Phanerochaete chrysosporium: involvement of veratryl alcohol

Phanerochaete chrysosporium decolorized several polyaromatic azo dyes in ligninolytic culture. The oxidation rates of individual dyes depended on their structures. Veratryl alcohol stimulated azo dye oxidation by pure lignin peroxidase (ligninase, LiP) in vitro. Accumulation of compound II of lignin peroxidase, an oxidized form of the enzyme, was observed after short incubations with these azo substrates. When veratryl alcohol was also present, only the native form of lignin peroxidase was observed. Azo dyes acted as inhibitors of veratryl alcohol oxidation. After an azo dye had been degraded, the oxidation rates of veratryl alcohol recovered, confirming that these two compounds competed for ligninase during the catalytic cycle. Veratryl alcohol acts as a third substrate (with H2O2 and the azo dye) in the lignin peroxidase cycle during oxidations of azo dyes.     

藜芦醇和吐温80对白腐菌产木质素降解酶的影响及在偶氮染料脱色中的作用

担子菌PM2在限氮液体培养下,分泌木质素过氧化物酶和锰过氧化物酶;藜芦醇、吐温 80的补充,提高了该菌锰过氧化物酶的产生,获得的最大锰过氧化物酶Mnp酶活为254.2u/L、190.2 u/L,分别是对照的3.4倍和2.5倍。选择三种偶氮染料,在染料体系下,进一步分析藜芦醇、吐温 80对担子菌PM2产过氧化物酶及染料脱色的影响。结果表明,担子菌PM2分泌的锰过氧化物酶Mnp与染料脱色有关,脱色程度受其分子结构特征影响;吐温80的补充,更有利于染料的脱色降解,48h后三种染料均可达到80%以上的脱色率。     

Decolorization of textile azo dyes by newly isolated halophilic and halotolerant bacteria

Studies were carried out on the decolorization of textile azo dyes by newly isolated halophilic and halotolerant bacteria. Among the 27 strains of halophilic and halotolerant bacteria isolated from effluents of textile industries, three showed remarkable ability in decolorizing the widely utilized azo dyes. Phenotypic characterization and phylogenetic analysis based on 16S rDNA sequence comparisons indicate that these strains belonged to the genus Halomonas. The three strains were able to decolorize azo dyes in a wide range of NaCl concentration (up to 20%w/v), temperature (25-40 degrees C), and pH (5-11) after 4 days of incubation in static culture. They could decolorize the mixture of dyes as well as pure dyes. These strains also readily grew in and decolorized the high concentrations of dye (5000 ppm) and could tolerate up to 10,000 ppm of the dye. UV-Vis analyses before and after decolorization and the colorless bacterial biomass after decolorization suggested that decolorization was due to biodegradation, rather than inactive surface adsorption. Analytical studies based on HPLC showed that the principal decolorization was reduction of the azo bond, followed by cleavage of the reduced bond.     

Degradation of azo dyes containing aminonaphthol by Sphingomonas sp strain 1CX

Sphingomonas sp strain 1CX was isolated from a wastewater treatment plant and is capable of aerobically degrading a suite of azo dyes, using them as a sole source of carbon and nitrogen. All azo dyes known to be decolorized by strain 1CX (Orange II, Acid Orange 8, Acid Orange 10, Acid Red 4, and Acid Red 88) have in their structure either 1-amino-2-naphthol or 2-amino-1-naphthol. In addition, an analysis of the structures of the dyes degraded suggests that there are certain positions and types of substituents on the azo dye which determine if degradation will occur. Growth and dye decolorization occurs only aerobically and does not occur under fermentative or denitrification conditions. The mechanism by which 1CX decolorizes azo dyes appears to be through reductive cleavage of the azo bond. In the case of Orange II, the initial degradation products were sulfanilic acid and 1-amino-2-naphthol. Sulfanilic acid, however, was not used by 1CX as a growth substrate. The addition of glucose or inorganic nitrogen inhibited growth and decoloration of azo dyes by 1CX. Attempts to grow the organism on chemically defined media containing several different amino acids and sugars as sources of nitrogen and carbon were not successful. Phylogenetic analysis of Sphingomonas sp strain 1CX shows it to be related to, but distinct from, other azo dye-decolorizing Sphingomonas spp strains isolated previously from the same wastewater treatment facility. Received 19 May 1999/ Accepted in revised form 11 August 1999     

Contribution of manganese peroxidase and laccase to dye decoloration by Trametes versicolor

During dye decoloration by Trametes versicolor ATCC 20869 in modified Kirk’s medium, manganese peroxidase (MnP) and laccase were produced, but not lignin peroxidase, cellobiose dehydrogenase or manganese-independent peroxidase. Purified MnP decolorized azo dyes [amaranth, reactive black 5 (RB5) and Cibacron brilliant yellow] in Mn²⁺-dependent reactions but did not decolorize an anthraquinone dye [Remazol brilliant blue R (RBBR)]. However, the purified laccase decolorized RBBR five to ten times faster than the azo dyes and the addition of a redox mediator, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), did not alter decoloration rates. Amaranth and RB5 were decolorized the most rapidly by MnP since they have a hydroxyl group in an ortho position and a sulfonate group in the meta position relative to the azo bond. During a typical batch decoloration with the fungal culture, the ratio of laccase:MnP was 10:1 to 20:1 (based on enzyme activity) and increased to greater than 30:1 after decoloration was complete. Since MnP decolorized amaranth about 30 times more rapidly than laccase per unit of enzyme activity, MnP should have contributed more to decoloration than laccase in batch cultures.     

Study of dye decolorization in an immobilized laccase enzyme-reactor using online spectroscopy

Decolorization of textile dyes by a laccase from Trametes modesta immobilized on gamma-aluminum oxide pellets was studied. An enzyme reactor was equipped with various UV/Vis spectroscopic sensors allowing the continuous online monitoring of the decolorization reactions. Decolorization of the dye solutions was followed via an immersion transmission probe. Adsorption processes were observed using diffuse reflectance measurements of the solid carrier material. Generally, immobilization of the laccase does not seem to sterically affect dye decolorization. A range of commercial textile dyes was screened for decolorization and it was found that the application of this enzymatic remediation system is not limited to a certain structural group of dyes. Anthrachinonic dyes (Lanaset Blue 2R, Terasil Pink 2GLA), some azo dyes, Indigo Carmine, and the triphenylmethane dye Crystal Violet were efficiently decolorized. However, the laccase displayed pronounced substrate specificities when a range of structurally related model azodyes was subjected to the biotransformation. Azodyes containing hydroxy groups in ortho or para position relative to the azo bond were preferentially oxidized. The reactor performance was studied more closely using Indigo Carmine.     

Reduction and partial degradation mechanisms of naphthylaminesulfonic azo dye amaranth by <Emphasis Type="Italic">Shewanella decolorationis</Emphasis> S12

Reduction and biodegradation mechanisms of naphthylaminesulfonic azo dye amaranth using a newly isolated Shewanella decolorationis strain S12 were investigated. Under anaerobic conditions, amaranth was reduced by strain S12, and a stoichiometric amount of two reduction products RP-1 and RP-2 were generated. UV/visible spectrophotometric and high performance liquid chromatography (HPLC) analysis indicated that RP-1 and RP-2 were 1-aminenaphthylene -4-sulfonic acid and 1-aminenaphthylene-2-hydroxy-3, 6-disulfonic acid. The result strongly supports a mechanism of azo dye reduction by the process via the reductive cleavage of the azo bond to form corresponding aromatic amines. The result of HPLC analyses revealed that these aromatic amines were not able to be mineralized by strain S12 under anaerobic conditions. But after re-aeration of the decolorized culture, RP-2 was mineralized completely by this microorganism, but the consumption of RP-1 was not observed. Ames test showed that amaranth had mutagenic but no cytotoxic potential. The mutagenic potential was relieved after the anaerobic treatment with strain S12 as the mutagenic effect of the two reduction products from amaranth was not detected by Ames test. Thus, the ability of strain S12 to reduce and partially mineralize the naphthylaminesulfonic azo dye efficiently was demonstrated, which can potentially be used to biodegrade and detoxify wastewater containing azo dyes using an alternating anaerobic/aerobic treatment procedure.     

Use of azo dye ligand chromatography for the partial purification of a novel extracellular peroxidase from Streptomyces viridosporus T7A

Crude peroxidase preparations from the lignocellulose-degrading actinomycete, Streptomyces viridosporus T7A, were shown to decolorize several azo dye isomers and showed a correlation of dye structure to degradability similar to that shown by fungal Mn-peroxidase, an enzyme not previously described in actinomycetes. Addition of the heme-peroxidase inhibitor KCN did not significantly change the ability of the T7A enzyme(s) to decompose the dyes. These results suggest that T7A may produce a Mn- or other peroxidase with similar substrate specificity to Mn-peroxidase. Affinity chromatography using immobilized azo dye isomers was used for purifying peroxidases from T7A. A significantly purified peroxidase preparation was obtained irrespective of the azo dye used. In comparison, concanavalin A lectin affinity chromatography showed very poor binding and resolution for T7A peroxidases. Azo dye affinity purification gave preparations sufficiently purified to allow amino acid microsequencing for two of the bound proteins. N-terminal amino acid sequences were found to share significant homology with a fungal Mn-peroxidase and actinomycete cellulases. Received: 20 May 1997 / Received revision: 17 December 1997 / Accepted: 2 January 1998     

Rapid decolorization of azo dyes by crude manganese peroxidase from Schizophyllum sp. F17 in solid-state fermentation

The production of ligninolytic enzymes by the fungus Schizophyllum sp. F17 using a cost-effective medium comprised of agro-industrial residues in solid-state fermentation (SSF) was optimized. The maximum activities of the enzymes manganese peroxidase (MnP), laccase (Lac), and lignin peroxidases (LiP) were 1,200, 586, and 109 U/L, respectively, on day 5 of SSF. In vitro decolorization of three structurally different azo dyes by the extracellular enzymes was monitored to determine its decolorization capability. The results indicated that crude MnP, but not LiP and Lac, played a crucial role in the decolorization of azo dyes. After optimization of the dye decolorization system with crude MnP, the decolorization rates of Orange IV and Orange G, at an initial dye concentration of 50 mg/L, were enhanced to 76 and 57%, respectively, after 20 min of reaction at pH 4 and 35°C. However, only 8% decolorization of Congo red was observed. This enzymatic reaction system revealed a rapid decolorization of azo dyes with a low MnP activity of 24 U/L. Thus, this study could be the basis for the production and application of MnP on a larger scale using a low-cost substrate.     

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.     

Biological sulphate reduction and redox mediator effects on azo dye decolourisation in anaerobic–aerobic sequencing batch reactors

In this work, the anaerobic period of an anaerobic–aerobic sequencing batch reactor was found to allow the reductive decolourisation of azo dyes. 1-l reactors were operated in 24-h cycles comprising anaerobic and aerobic reaction phases, fed with a simulated textile effluent including a reactive type (Remazol Brilliant Violet 5R) or an acid type (Acid Orange 7) azo dye. The aim was to assess the role of different redox phenomena in the anaerobic decolourisation process. Selective inhibition of sulphate reducing bacteria was carried out in the sulphate-containing, reactive dye fed reactor, resulting in nearly complete, though reversible and inhibition of decolourisation. The acid dye fed reactor's supplementation with sulphate, though resulting in sulphate reduction, did not improve decolourisation. Other redox mediators, namely quinones, were more effective in promoting electron transfer to the azo bond. Bio-augmentation of the acid dye fed reactor with a pure sulphate reducer strain known to decolourise azo dyes, Desulfovibrio alaskensis, was also carried out. Decolourisation was improved, but apparently as a result of the carbon source change required to support D. alaskensis growth. A chemically mediated reduction of the azo bond coupled to biological sulphate reduction, thus seemed to account for the high decolourisation yields of both dyes.     

Biodegradation of diazo dye Direct brown MR by Acinetobacter calcoaceticus NCIM 2890

Acinetobacter calcoaceticus was employed for the degradation of Direct brown MR (DBMR), commercially used azo dye in the textile industry in order to analyze mechanism of the degradation and role of inhibitors, redox mediators and stabilizers of lignin peroxidase during decolorization. Induction of intracellular and extracellular lignin peroxidase, intracellular laccase and DCIP reductase represented their involvement in the biodegradation of DBMR. Decolorization and biodegradation of azo dye DBMR in broth were monitored by UV–visible spectrophotometer and TLC. The products obtained from A. calcoaceticus degradation were characterized by FTIR and identified by GC/MS as biphenyl amine, biphenyl, 3-amino 6-hydroxybenzoic acid and naphthalene diazonium. Germination (%) and growth efficiency of Sorghum vulgare and Phaseolus mungo seeds revealed the degradation of DBMR into less toxic products than original dye. A. calcoaceticus also has a potential to degrade diverse dyes present in the textile effluent, into nontoxic metabolites, hence A. calcoaceticus can be applied for the commercial application.     

撕裂蜡孔菌在开放体系中对甲基橙染料的静态脱色研究

为了评价撕裂蜡孔菌处理偶氮染料的应用潜力,用性能稳定的甲基橙染料为材料,采用批次试验在开放性体系中研究了染料初始浓度、菌丝生物量、温度、pH等因素对该菌脱色能力的影响,运用菌丝体反接、染液光谱扫描、菌丝体显微观察等方法探讨了菌丝体脱色的可能机制,利用植物萌发试验进行了染料和脱色后溶液的毒性测试。结果表明,撕裂蜡孔菌在开放的静止体系中能够对甲基橙高效脱色,其最适脱色温度为35℃,最佳脱色pH值在6左右。菌丝对甲基橙的脱色表现在吸附和产酶降解两个方面,脱色过程中染料对菌丝体本身的影响较少。植物毒性分析显示撕裂蜡孔菌脱色48h后的产物对植物的毒性比甲基橙本身更强,若要彻底降解可能需要较长时间。本研究可为染料脱色工艺提供新的菌种。     

The effect of azo dyes on heat aggregation of IgG

The mechanism of IgG heat aggregation was studied using IgG aggregates complexed with azo dyes to increase their solubility and stability. Heat dependent and heat independent steps of aggregation were differentiated. On heating IgG at the dye concentration exceeding 100 times that of protein, mainly dimers are formed, as judged from ultracentrifugation and chromatographic analysis, whereas high molecular weight derivatives appear at room temperature when the protein/dye ratio is decreased. The analysis of spectral changes following either the attachment or removal of the dye from IgG aggregates implies that only a part of the dye molecules is bound firmly and directly to the protein binding sites. These dye molecules which are easily removed by adsorption to cellulose or reduced by dithionate but migrate together with IgG aggregates on chromatography and electrophoresis, are supposed to constitute that part of the micelle which extrudes from the binding site and, hence, is fixed indirectly to protein. Various proteins with predominant beta-structure were also found to bind azo dyes when heated.     

Developing azo and formazan dyes based on environmental considerations: Salmonella mutagenicity

In previous papers, the synthesis and chemical properties of iron-complexed azo and formazan dyes were reported. It was shown that in certain cases iron could be substituted for the traditionally used metals such as chromium and cobalt, without having an adverse effect on dye stability. While these results suggested that the iron analogs were potential replacements for the commercially used chromium and cobalt prototypes, characterization of potentially adverse environmental effects of the new dyes was deemed an essential step in their further development. The present paper provides results from using the Salmonella/mammalian microsome assay to determine the mutagenicity of some important commercial metal complexed dyes, their unmetallized forms, and the corresponding iron-complexed analogs. The study compared the mutagenic properties of six unmetallized azo dyes, six commercial cobalt- or chromium-complexed azo dyes, six iron-complexed azo dyes, six unmetallized formazan dyes, and six iron-complexed formazan dyes. The results of this study suggest that the mutagenicity of the unmetallized dye precursors plays a role in determining the mutagenicity of the iron-complexes. For the monoazo dye containing a nitro group, metal complex formation using iron or chromium decreased or removed mutagenicity in TA100; however, little reduction in mutagenicity was noted in TA98. For the formazan dye containing a nitro group, metal-complex formation using iron increased mutagenicity. Results varied for metal-complexes of azo and formazan dyes without nitro groups, but in general, the metal-complexed dyes based on mutagenic ligands were also mutagenic, while those dyes based on nonmutagenic ligands were nonmutagenic.     

Evaluation of metabolism of azo dyes and their effects on <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> metabolome

Dyes containing one or more azo linkages are widely applied in cosmetics, tattooing, food and drinks, pharmaceuticals, printing inks, plastics, leather, as well as paper industries. Previously we reported that bacteria living on human skin have the ability to reduce some azo dyes to aromatic amines, which raises potential safety concerns regarding human dermal exposure to azo dyes such as those in tattoo ink and cosmetic colorant formulations. To comprehensively investigate azo dye-induced toxicity by skin bacteria activation, it is very critical to understand the mechanism of metabolism of the azo dyes at the systems biology level. In this study, an LC/MS-based metabolomics approach was employed to globally investigate metabolism of azo dyes by Staphylococcus aureus as well as their effects on the metabolome of the bacterium. Growth of S. aureus in the presence of Sudan III or Orange II was not affected during the incubation period. Metabolomics results showed that Sudan III was metabolized to 4-(phenyldiazenyl) aniline (48%), 1-[(4-aminophenyl) diazenyl]-2-naphthol (4%) and eicosenoic acid Sudan III (0.9%). These findings indicated that the azo bond close to naphthalene group of Sudan III was preferentially cleaved compared with the other azo bond. The metabolite from Orange II was identified as 4-aminobenzene sulfonic acid (35%). A much higher amount of Orange II (~90×) was detected in the cell pellets from the active viable cells compared with those from boiled cells incubated with the same concentration of Orange II. This finding suggests that Orange II was primarily transported into the S. aureus cells for metabolism, instead of the theory that the azo dye metabolism occurs extracellularly. In addition, the metabolomics results showed that Sudan III affected energy pathways of the S. aureus cells, while Orange II had less noticeable effects on the cells. In summary, this study provided novel information regarding azo dye metabolism by the skin bacterium, the effects of azo dyes on the bacterial cells and the important role on the toxicity and/or inactivation of these compounds due to microbial metabolism.