Molecular cloning and characterization of the gene coding for the aerobic azoreductase from Xenophilus azovorans KF46F

Abstract

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.

FIG. 1.

DNA sequence and amino acid sequence of the azoreductase from X. azovorans KF46F. The N-terminal and two internal amino acid sequences, which were determined by chemical Edman degradation, are underlined. The stop codon is indicated by a dash. The amino acids putatively involved in NAD(P)H binding are boxed.