Partial Purification and Characterization of the Recombinant Benzaldehyde Dehydrogenase from Rhodococcus ruber UKMP-5M

Background: Benzaldehyde dehydrogenase (BZDH) is encoded by the xylC that catalyzes the conversion of benzaldehyde into benzoate in many pathways such as toluene degradation. Objectives: In this study, the xylC gene from Rhodococcus ruber UKMP-5M was expressed in Escherichia coli, purified, and characterized.Materials and Methods: The xylC was amplified and cloned in E. coli. The recombinant plasmid pGEMT-xylC was digested by NdeI and HindIII to construct plasmid pET28b-xylC and transformed in E. coli BL21 (DE3). Expression of the recombinant protein was induced by 1 mM isopropyl β-D-thiogalactoside (IPTG) at 37 °C. The BZDH was purified by ion exchange chromatography, in which the product was an NAD-dependent enzyme using benzaldehyde as a substrate for enzyme characterization. The end metabolite was identified via gas chromatography mass spectrometry (GC-MS). Results: The recombinant BZDH is 27 kDa, purified by ion exchange chromatography. The activity of BZDH was 9.4 U/ml. The optimum pH and temperature were 8.5 and 25 ºC, respectively. The Michaelis constant (Km) and maximum velocity (Vmax) were 4.2 mM and 19.7 U/ml, respectively. The metabolite of BZDH was benzene carboxylic acid as determined by GC-MS analysis. Conclusion: BZDH has the ability to degrade benzaldehyde to less toxic compounds. The BZDH is a critical enzyme for the degradation of aromatic hydrocarbons in Rhodococcus sp. The BZDH from R. ruber UKMP-5M is showed similar function with other aldehyde dehydrogenases.