The gene coding for an aerobic azoreductase was cloned from Xenophilus azovorans KF46F (formerly Pseudomonas sp. strain KF46F), which was previously shown to grow with the carboxylated azo compound 1-(4-carboxyphenylazo)-2-naphthol (carboxy-Orange II) as the sole source of carbon and energy. The deduced amino acid sequence encoded a protein with a molecular weight of 30,278 and showed no significant homology to amino acid sequences currently deposited at the relevant data bases. A presumed NAD(P)H-binding site was identified in the amino-terminal region of the azoreductase. The enzyme was heterologously expressed in Escherichia coli and the azoreductase activities of resting cells and cell extracts were compared. The results suggested that whole cells of the recombinant E. coli strains were unable to take up sulfonated azo dyes and therefore did not show in vivo azoreductase activity. The turnover of several industrially relevant azo dyes by cell extracts from the recombinant E. coli strain was demonstrated.Azo dyes are characterized by the presence of one or more azo groups (-NAN-). They are the largest and most versatile class of dyes, and more than half of the annually produced dyes (estimated for 1994 worldwide as about 1 million tons) are azo dyes. Presumably more than 2,000 different azo dyes are currently used for the dyeing of various materials such as textiles, leather, plastics, cosmetics, and food (2,9,11,36,50).Azo dyes are generally considered to be xenobiotic compounds which are rather recalcitrant against biodegradative processes in conventional sewage treatment systems (33,40). Nevertheless, during the last years it has been demonstrated that several microorganisms are able to transform azo dyes to noncolored products or even mineralize them completely under certain environmental conditions. There are numerous reports which describe the reductive cleavage of azo dyes under anaerobic conditions which result in the decolorization of azo dyes. 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 very often low-molecular-weight redox mediators (e.g., flavins or quinones) are involved (10,22,24,35,42).Some aerobic biotransformations of azo dyes by fungi and bacteria are also known. Thus, various lignolytic fungi were shown to decolorize azo dyes using ligninases, manganese peroxidases, or laccases (8). Only very few aerobic bacteria which can grow with azo compounds have been described. The ability of bacteria to grow with simple carboxylated azo compounds as the sole source of carbon and energy was shown first by Overney (32) who isolated a "Flavobacterium" which was able to grow aerobically with the model compound 4,4Ј-dicarboxyazobenzene. In subsequent work, it was shown that 4,4Ј-dicarboxyazobenzene-degrading mixed bacterial cultures could be adapted after prolonged continuous cultivation for several hundreds of generations under nonsterile conditions to t...

The gene coding for an aerobic azoreductase was cloned from Pigmentiphaga kullae K24, which is able to grow with the carboxylated azo compound 1-(4'-carboxyphenylazo)-4-naphthol (carboxy-Orange I) as sole source of carbon and energy. The gene encoded a protein with a molecular weight of 20,557 Da, with a conserved putative NAD(P)H-binding site in the amino-terminal region. The deduced amino acid sequence showed no further significant sequence homologies to previously studied aerobic azoreductases. The azoreductase was heterologously expressed in Escherichia coli and shown to convert the sulfonated azo dye Orange I and furthermore Magneson II [4-(4-nitrophenylazo)-1-naphthol].

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NOTET with the name Pigmentiphaga kullae gen. nov., sp. nov.