Mutagenicity of selected sulfonated azo dyes in the Salmonella/microsome assay: use of aerobic and anaerobic activation procedures

A selection of 16 sulfonated azo dyes of both the monoazo type and diazo dyes based on benzidine, o-tolidine and o-dianisidine were assayed for mutagenicity in Salmonella typhimurium strains TA98 and TA100 employing both aerobic and anaerobic preincubation procedures. 3 food dyes, FD & C Red No. 40 and Yellows No. 5 and No. 6 were non-mutagenic in all tests. 5 dyes were mutagenic with aerobic treatment (trypan blue, Pontacyl Sky Blue 4BX, Congo Red, Eriochrome Blue Black B, dimethylaminoazobenzene) and 6 were mutagenic aerobically with riboflavin and cofactors (Deltapurpurin, trypan blue, Pontacyl Sky Blue 4BX, Congo Red, methyl orange, Ponceau 3R). Anaerobic preincubation involving enzymatic reduction of the dyes led to a different pattern of mutagenicity, with trypan blue giving much enhanced mutagenicity; Eriochrome Blue Black B, Pontacyl Sky Blue 4BX, Deltapurpurin and Congo Red exhibiting similar activity to aerobic preincubation; and methyl orange and Ponceau 3R yielding no mutagenicity. The results are interpreted with respect to an hypothesis involving partial reduction of the azo bond under differing degrees of aerobiosis via azo-anion radicals and hydrazo intermediates.     

Mutagenicity test of dyes used in cosmetics with the Salmonella/mammalian-microsome test.

37 dyes including 3 anthraquinone, 22 azo; 5 xanthene, 5 fluorandiol, and 2 thioindigo dyes, were tested for mutagenic potential with the Salmonella/mammalian-microsome test. Two frame-shift histidine mutants (TA1537 and TA98) and two base-pair substituted histidine mutants (TA1535 and TA100) of Salmonella typhimurium were employed. Both the spot test and the plate-incorporation assay indicated that one azo dye, D&C Orange No. 17, was mutagenic with three of the bacterial test strains. The mutagenic response of D&C Orange No. 17 was depressed by the addition of the microsomal fractions from rat livers. Of the chemicals used to synthesize D&C Orange No; 17 was depressed by the addition of the microsomal fractions from rat livers. Of the chemicals used to synthesize D&C Orange No. 17, beta-naphthol was not mutagenic but 2,4-dinitroaniline was mutagenic to the same Salmonella strains as D&C Orange No. 17 . Dimethyl sulfoxide extracts of lipsticks of similar formula but without D&C Orange No. 17 were tested in the plate incorporation assay. Only those containing D&C Orange No. 17 were mutagenic and the dye was mutagenic at concentrations consumed in normal daily use.     

The significance of azo-reduction in the mutagenesis and carcinogenesis of azo dyes

Azo dyes are widely used in textile, printing, cosmetic, drug and food-processing industries. They are also used extensively in laboratories as either biological stains or pH indicators. The extent of such use is related to the degree of industrialization. Since intestinal cancer is more common in highly industrialized countries, a possible connection may exist between the increase in the number of cancer cases and the use of azo dyes. Azo dyes can be reduced to aromatic amines by the intestinal microflora. The mutagenicity of a number of azo dyes is reviewed in this paper. They include Trypan Blue, Ponceau 3R, Pinceau 2R, Methyl Red, Methyl Yellow, Methyl Orange, Lithol Red, Orange I, Orange II, 4-Phenylazo-Naphthylamine, Sudan I, Sudan IV, Acid Alizarin Violet N, Fast Garnet GBC, Allura Red, Ponceau SX, Sunset Yellow, Tartrazine, Citrus Red No. 2, Orange B, Yellow AB, Carmoisine, Mercury Orange, Ponceau S, Versatint Blue, Phenylazophenol, Evan's Blue and their degraded aromatic amines. The significance of azo reduction in the mutagenesis and carcinogenesis of azo dyes is discussed.     

Evaluation of azo food dyes for mutagenicity and inhibition of mutagenicity by methods using Salmonella typhimurium

The mutagenicity of 4 azo dyes (FD&C Yellow No. 5, FD&C Yellow No. 6, FD&C Red No. 40 and amaranth) that are widely used to color food has been evaluated. 4 different methods were used: (1) the standard Ames plate-incorporation assay performed directly on the dyes in the absence of S9 and in the presence of rat- or hamster-liver S9; (2) application of the standard plate assay to ether extracts of aqueous solutions of the dyes; (3) a variant of the standard assay, using hamster liver S9, preincubation, flavin mononucleotide (FMN) and other modifications designed to facilitate azo reduction; and (4) reduction of the dyes with sodium dithionite, followed by ether extraction and the standard plate assay. Assays that include chemical reduction (methods 3 and 4) were included because azo compounds ingested orally are reduced in the intestine with the release of free aromatic amines. No mutagenic activity was seen for any of the azo dyes tested by using the standard Ames plate assay (method 1). Ether extracts of some samples of FD&C Yellow No. 6, FD&C Red No. 40 and amaranth were active (method 2), but only at high doses, generally 250 mg-equivalents or more per plate. These results indicate the presence of low levels of ether-extractable mutagenic impurities. The FMN preincubation assay (method 3) gave negative results for all dye samples tested. Most batches of FD&C Red No. 40 tested had mutagenic activity that was detectable when the ether extract of less than 1 mg of dithionite-reduced dye was plated in the presence of S9 (method 4). This finding implies that an impurity in these samples of FD&C Red No. 40 can be reduced to yield an ether-extractable mutagen. Dithionite-reduced samples of FD&C Yellow No. 6 and amaranth showed ether-extractable mutagenic activity only at much higher doses than those at which activity was seen with most dithionite-reduced samples of FD&C Red No. 40 (method 4). FD&C Yellow No. 5 showed no mutagenic activity with this method. Mutagenic activity was not detected when FD&C Red No. 40 was tested by using the azo reduction preincubation assay with FMN (method 3).(ABSTRACT TRUNCATED AT 400 WORDS)     

Mutagenicity of benzidine and benzidine-congener dyes and selected monoazo dyes in a modified Salmonella assay

We have evaluated the mutagenic activity of a series of diazo compounds derived from benzidine and its congeners o-tolidine, o-dianisidine and 3,3'-dichlorobenzidine as well as several monoazo compounds. The test system used was a modification of the standard Ames Salmonella assay in which FMN, hamster liver S9 and a preincubation step are used to facilitate azo reduction and detection of the resulting mutagenic aromatic amines. All of the benzidine and o-tolidine dyes tested were clearly mutagenic. The o-dianisidine dyes except for Direct Blue 218 were also mutagenic. Direct Blue 218 is a copper complex of the mutagenic o-dianisidine dye Direct Blue 15. Pigment Yellow 12, which is derived from 3,3'-dichlorobenzidine, could not be detected as mutagenic, presumably because of its lack of solubility in the test reaction mixture. Of the monoazo dyes tested, methyl orange was clearly mutagenic, while C.I. Acid Red 26 and Acid Dye (C.I. 16155; often referred to as Ponceau 3R) had marginal to weak mutagenic activity. Several commercial dye samples had greater mutagenic activity with the modified test protocol than did equimolar quantities of their mutagenic aromatic amine reduction products. Investigation of this phenomenon for Direct Black 38 and trypan blue showed that it was due to the presence of mutagenic impurities in these samples. The modified method used appears to be suitable for testing the mutagenicity of azo dyes, and it may also be useful for monitoring the presence of mutagenic or potentially carcinogenic impurities in otherwise nonmutagenic azo dyes.     

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.     

Enhanced bio-decolorization of azo dyes by quinone-functionalized ceramsites under saline conditions

Anthraquinone-2-sulfonate was immobilized on ceramsites (AQS-ceramsites) using a novel adsorption/covalence coupling method and their effects on the anaerobic bio-decolorization rates of azo dyes by salt-tolerant AQS-reducing (STAR) community were investigated. The results showed that AQS-ceramsites mediated specific bio-decolorization rates of four azo dyes Acid Yellow 36, Reactive Red 2, Acid Red 27 and Acid Orange 7 increase 2.3–6.4 fold than those lacking ceramsites in the presence of 50 g/L NaCl. Moreover, repeated experiments with AQS-ceramsites showed that the decolorization efficiencies of azo dyes could remain over 98% of their original value. These results indicated that AQS-ceramsites functioning as redox mediators exhibited good catalytic activity and stability under saline conditions. The dynamics of the STAR community structure revealed by PCR-DGGE also showed that the presence of AQS-ceramsites made STAR bacteria keeping predominant in the catalytic system. Therefore, it can be concluded that this novel solid redox mediator is potentially useful for the treatment of saline dye wastewater.     

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.     

Biodegradation of azo dyes in cocultures of anaerobic granular sludge with aerobic aromatic amine degrading enrichment cultures

A prerequisite for the mineralization (complete biodegradation) of many azo dyes is a combination of reductive and oxidative steps. In this study, the biodegradation of two azo dyes, 4-phenylazophenol (4-PAP) and Mordant Yellow 10 (4-sulfophenylazo-salicylic acid; MY10), was evaluated in batch experiments where anaerobic and aerobic conditions were integrated by exposing anaerobic granular sludge to oxygen. Under these conditions, the azo dyes were reduced, resulting in a temporal accumulation of aromatic amines. 4-Aminophenol (4-AP) and aniline were detected from the reduction of 4-PAP. 5-Aminosalicylic acid (5-ASA) and sulfanilic acid (SA) were detected from the reduction of MY10. Subsequently, aniline was degraded further in the presence of oxygen by the facultative aerobic bacteria present in the anaerobic granular sludge. 5-ASA and SA were also degraded, if inocula from aerobic enrichment cultures were added to the batch experiments. Due to rapid autoxidation of 4-AP, no enrichment culture could be established for this compound. The results of this study indicate that aerobic enrichment cultures developed on aromatic amines combined with oxygen-tolerant anaerobic granular sludge can potentially be used to completely biodegrade azo dyes under integrated anaerobic/aerobic conditions. Received: 16 September 1998 / Received revision: 14 December 1998 / Accepted: 21 December 1998     

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.     

Azo-dye degradation in an anaerobic-aerobic treatment system operating on simulated textile effluent

 Decolorisation of azo dyes during biological effluent treatment can involve both adsorption to cell biomass and degradation by azo-bond reduction during anaerobic digestion. Degradation is expected to form aromatic amines, which may be toxic and recalcitrant to anaerobic treatment but degradable aerobically. Methods for the quantitative detection of substituted aromatic amines arising from azo-dye cleavage are complex. A simple qualitative method is suggested as a way in which to investigate whether decolorisation is actually due to degradation, and whether the amines generated are successfully removed by aerobic treatment. Samples from a combined anaerobic-aerobic system used for treating a simulated textile wastewater containing the reactive azo dye Procion Red H-E7B were analysed by high-performance liquid chromatoraphy/ultraviolet (HPLC-UV) methods. Anaerobic treatment gave significant decolorisation, and respiration-inhibition tests showed that the anaerobic effluent had an increased toxicity, suggesting azo-dye degradation. The HPLC method showed that more polar, UV-absorbing compounds had been generated. Aerobically, these compounds were removed or converted to highly polar compounds, as shown by HPLC analysis. Since the total organic nitrogen (TON) decreased aerobically as organic N-containing compounds were mineralised, aromatic amine degradation is suggested. Although only a simple qualitative HPLC method was used, colour removal, toxicity and TON removal all support its usefulness in analysing biotreatment of azo dyes. Received: 2 August 1999 / Accepted: 3 September 1999     

Correlation of anaerobic biodegradability and the electrochemical characteristic of azo dyes

Some experiments were conducted to study some electrochemical factors affecting the bacterial reduction (cleavage) of azo dyes, knowledge of which will be useful in the wastewater treatments of azo dyes. A common mixed culture was used as a test organism and the reductions of Acid Yellow 4, 11, 17 and Acid Yellow BIS were studied. It was found that the azo dyes were reduced at different rates, which could be correlated with the reduction potential of the azo compounds in cyclic voltammetric experiments. Acid Yellow BIS (E _r − 616.75 mV) was reduced at the highest rate of 0.0284 mol g dry cell weight⁻¹ h⁻¹, Acid Yellow 11 (E _r − 593.25 mV) at 0.0245 mol g dry cell weight⁻¹ h⁻¹ and Acid Yellow 4 (E _r − 513 mV) at 0.0178 mol g dry cell weight⁻¹ h⁻¹. At the same time, the decolourization rate of Acid Yellow 17 (E _r − 627.5 mV) was 0.0238 mol g dry cell weight⁻¹ h⁻¹, which was affected by the nature of chlorine substituent. Reduction of these azo dyes did not occur under aeration conditions. These studies with a common mixed culture indicate that the reduction of azo dyes may be influenced by the chemical nature of the azo compound. The reduction potential is a preliminary tool to predict the decolourization capacity of oxidative and reductive biocatalysts.     

Monoazo and diazo dye decolourisation studies in a methanogenic UASB reactor

Mixed anaerobic bacterial consortia have been show to reduce azo dyes and batch decolourisation tests have also demonstrated that predominantly methanogenic cultures also perform azo bond cleavage. The anaerobic treatment of wool dyeing effluents, which contain acetic acid, could thus be improved with a better knowledge of methanogenic dye degradation. Therefore, the decolourisation of two azo textile dyes, a monoazo dye (Acid Orange 7, AO7) and a diazo dye (Direct Red 254, DR254), was investigated in a methanogenic laboratory-scale Upflow Anaerobic Sludge Blanket (UASB), fed with acetate as primary carbon source. As dye concentration was increased a decrease in total COD removal was observed, but the acetate load removal (90%) remained almost constant. A colour removal level higher than 88% was achieved for both dyes at a HRT of 24h. The identification by HPLC analysis of sulfanilic acid, a dye reduction metabolite, in the treated effluent, confirmed that the decolourisation process was due mainly to azo bond reduction. Although, HPLC chromatograms showed that 1-amino-2-naphthol, the other AO7 cleavage metabolite, was removed, aeration batch assays demonstrated that this could be due to auto-oxidation and not biological mineralization. At a HRT of 8h, a more extensive reductive biotransformation was observed for DR254 (82%) than for AO7 (56%). In order to explain this behaviour, the influence of the dye aggregation process and chemical structure of the dye molecules are discussed in the present work.     

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.     

Identification of quinoide redox mediators that are formed during the degradation of naphthalene-2-sulfonate by Sphingomonas xenophaga BN6

During aerobic degradation of naphthalene-2-sulfonate (2NS), Sphingomonas xenophaga strain BN6 produces redox mediators which significantly increase the ability of the strain to reduce azo dyes under anaerobic conditions. It was previously suggested that 1,2-dihydroxynaphthalene (1,2-DHN), which is an intermediate in the degradative pathway of 2NS, is the precursor of these redox mediators. In order to analyze the importance of the formation of 1,2-DHN, the dihydroxynaphthalene dioxygenase gene (nsaC) was disrupted by gene replacement. The resulting strain, strain AKE1, did not degrade 2NS to salicylate. After aerobic preincubation with 2NS, strain AKE1 exhibited much higher reduction capacities for azo dyes under anaerobic conditions than the wild-type strain exhibited. Several compounds were present in the culture supernatants which enhanced the ability of S. xenophaga BN6 to reduce azo dyes under anaerobic conditions. Two major redox mediators were purified from the culture supernatants, and they were identified by high-performance liquid chromatography-mass spectrometry and comparison with chemically synthesized standards as 4-amino-1,2-naphthoquinone and 4-ethanolamino-1,2-naphthoquinone.     

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)     

Enzymatic reduction of azo and indigoid compounds

A customer- and environment-friendly method for the decolorization azo dyes was developed. Azoreductases could be used both to bleach hair dyed with azo dyes and to reduce dyes in vat dyeing of textiles. A new reduced nicotinamide adenine dinucleotide-dependent azoreductase of Bacillus cereus, which showed high potential for reduction of these dyes, was purified using a combination of ammonium sulfate precipitation and chromatography and had a molecular mass of 21.5 kDa. The optimum pH of the azoreductase depended on the substrate and was within the range of pH 6 to 7, while the maximum temperature was reached at 40°C. Oxygen was shown to be an alternative electron acceptor to azo compounds and must therefore be excluded during enzymatic dye reduction. Biotransformation of the azo dyes Flame Orange and Ruby Red was studied in more detail using UV-visible spectroscopy, high-performance liquid chromatography, and mass spectrometry (MS). Reduction of the azo bonds leads to cleavage of the dyes resulting in the cleavage product 2-amino-1,3 dimethylimidazolium and N∼1∼,N∼1∼-dimethyl-1,4-benzenediamine for Ruby Red, while only the first was detected for Flame Orange because of MS instability of the expected 1,4-benzenediamine. The azoreductase was also found to reduce vat dyes like Indigo Carmine (C.I. Acid Blue 74). Hydrogen peroxide (H₂O₂) as an oxidizing agent was used to reoxidize the dye into the initial form. The reduction and oxidation mechanism of Indigo Carmine was studied using UV-visible spectroscopy.     

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)     

Decolorization of Acid Red 27 and Reactive Red 2 by <Emphasis Type="Italic">Enterococcus faecalis</Emphasis> under a batch system

The objectives of this study were to investigate: (1) the capacity of Enterococcus faecalis on the decolorization of the azo dyes Acid Red 27 and Reactive Red 2; and (2) the growth characteristics of E. faecalis on those dyes. E. faecalis was able to decolorize Acid Red 27 and Reactive Red 2 effectively. High decolorization efficiency (95–100%) was achieved within 3 h of incubation for Acid Red 27, and 12 h for Reactive Red 2, at room temperature, neutral pH, static and non-aerated condition. Growth characteristics of E. faecalis on azo dyes, which were indicated by cell growth rate, biomass production, and growth yield, was worse than the control. E. faecalis grew better on Acid Red 27 rather than Reactive Red 2.     

Modification of azo dyes by lactic acid bacteria

Aim:  The ability of Lactobacillus casei and Lactobacillus paracasei to modify the azo dye, tartrazine, was recently documented as the result of the investigation on red coloured spoilage in acidified cucumbers. Fourteen other lactic acid bacteria (LAB) were screened for their capability to modify the food colouring tartrazine and other azo dyes of relevance for the textile industry.
Methods and Results:  Most LAB modified tartrazine under anaerobic conditions, but not under aerobic conditions in modified chemically defined media. Microbial growth was not affected by the presence of the azo dyes in the culture medium. The product of the tartrazine modification by LAB was identified as a molecule 111 daltons larger than its precursor by liquid chromatography-mass spectrometry. This product had a purple colour under aerobic conditions and was colourless under anaerobic conditions. It absorbed light at 361 and 553 nm.
Conclusion:  LAB are capable of anabolizing azo dyes only under anaerobic conditions.
Impact and Significance of the Study:  Although micro-organisms capable of reducing the azo bond on multiple dyes have been known for decades, this is the first report of anabolism of azo dyes by food related micro-organisms, such as LAB.