Cloning and characterization of a Flavin-free oxygen-insensitive azoreductase from Klebsiella oxytoca GS-4-08

ObjectivesThis study reports the identification of a new bacterial azoreductase (AzoR) from Klebsiella oxytoca GS-4-08, its heterologous production in Escherichia coli and the decolorization of azo dyes.ResultsThe AzoR, as a flavin-free, oxygen-insensitive enzyme, has a molecular mass of 22kDa and a high substrate specificity for methyl red (MR). In the presence of 5mM of NADH, the enzyme activity for decolorization of 50mgl(-1) of MR reached 5.61molmin(-1) mg protein(-1). Double-reciprocal plots indicated that the NADH and MR reductions proceed by ping-pong mechanism. The calculated V-m was 8.17Mmin(-1) mg protein(-1), and the AzoR retained over 75% of relative activity under temperature range from 20 to 50 degrees C.ConclusionThis study for the first time identified an AzoR from Klebsiella oxytoca strain, which enabled efficient degradation of azo dyes by strain GS-4-08.