Sulfonated azo compounds such as Mordant Yellow 3 are widely used as dyes for textiles, food, and cosmetics industries. Both aromatic sulfonic acids and azo groups are rare among natural products and thus confer a xenobiotic character to sulfonated azo dyes. In conventional sewage plants, certain aromatic compounds carrying sulfonic acid groups as substituents resist biodegradation or are incompletely degraded.
Haug et al. (1991) found that Pseudomonas sp. BN6 mineralised Mordant Yellow 3 to produce stoichiometric amounts of 6-Amino-2-naphthalenesulfonic acid (6A2NS) and 5-Aminosalicylate(5AS) that were excreted into the growth media (under anoxic growth conditions). The enzyme catalysing this reduction is a highly non-specific azo reductase. Products of this step in turn become substrates for further degradation via the aerobic 6-Amino-2-naphthalene sulfonic acid pathway, initiated by naphthalene 1,2-dioxygenase. This versatile enzyme has many other catalytic abilities, which are documented in a table of the Reactions of Naphthalene 1,2-Dioxygenase.
Various biological systems have also been known to posess the capability to cleave the azo bond reductively under anaerobic conditions. In mammalian tissues, azo reductase activity is primarily found in the liver. Consequently intestinal flora have also been found to reduce azo bonds, namely Streptococcus faecalis.
The degradative process for 6-Amino-2-Naphthalene sulfonic acid as well as 5 Aminosalicylate are both aerobic processes that are performed by two strains in conjunction namely Pseudomonas sp. BN6 and Pseudomonas sp. BN9. Strain BN6 under aerobic conditions catalyses the conversion of 6A2NS to 5AS with the release of pyruvate as an energy source. Strain BN9 (again under aerobic growth conditions) was found to be responsible for the biotransformation of 5AS to Fumarate and Pyruvate (Stolz and Knackmuss, 1992).
5 AS which is identified as an intermediate in the bacterial degradation of aminonaphthalenesulfonates, has furtheremore been identified as an active agent in many drugs being developed for treatment of ulcerative colitis.
The following is a text-format pathway map. Follow the links for more information on compounds or reactions. This map is also available in graphic (33k) format.
Mordant yellow 3 Pseudomonas sp. BN6 Anaerobic | | | azo reductase | | v 5-Aminosalicylate<---+--->6-Amino-2-naphthalenesulfonic acid | | | | naphthalene | | 1,2-dioxygenase | | | V | 6-Amino-1,2-dihydroxy | -naphthalene | | | | 1,2-dihydroxy | | naphthalene | | dioxygenase | | | v | 6-Amino-2-hydroxychromene | -2-carboxylate | | | | 2-hydroxychromene-2- | | carboxylate isomerase | | | v | 3E-4-(5-Amino-2-hydroxy phenyl) | -2-oxo-but-3-ene-1-oic acid | | | | tHBPA | | hydratase-aldolase | | | v | 5-Aminosalicylaldehyde | | | | salicylaldehyde | | dehydrogenase | | | v +-----------------------> 5-Aminosalicylate Pseudomonas sp. BN9 Aerobic | | 5 aminosalicylate | dioxygenase | v cis-4-Amino-6-carboxy- 2-oxo-hexa-3,5 dienoate | | spontaneous | | v trans-4-Amino-6-carboxy- 2-oxo-hexa-3,5 dienoate | | trans ACOHDA | hydrolase | v Fumarylpyruvate | | fumarylpyruvate | hydrolase | v Pyruvate + Fumarate | | | | | | | | | | v v Intermediary Intermediary Metabolism Metabolism (KEGG) (KEGG)
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