Cloning and characterization of enoate reductase with high β-ionone to dihydro-β-ionone bioconversion productivity

Background: Dihydro-beta-ionone is a principal aroma compound and has received considerable attention by flavor and fragrance industry. The traditional method of preparing dihydro-beta-ionone has many drawbacks, which has restricted its industrial application. Therefore, it is necessary to find a biotechnological method to produce dihydro-beta-ionone. Results: In this study, the enoate reductase with high conversion efficiency of beta-ionone to dihydro beta-ionone, DBR1, was obtained by screening four genetically engineered bacteria. The product, dihydro-beta-ionone, was analyzed by GC and GC-MS. The highest dihydro-beta-ionone production with 308.3 mg/L was detected in the recombinant strain expressing DBR1 which was later on expressed and purified. Its optimal temperature and pH were 45 degrees C and 6.5, respectively. The greatest activity of the purified enzyme was 356.39 U/mg using beta-ionone as substrate. In the enzymatic conversion system, 1 mM of beta-ionone was transformed into 91.08 mg/L of dihydro-beta-ionone with 93.80% of molar conversion. Conclusion: DBR1 had high selectivity to hydrogenated the 10,11-unsaturated double bond of beta-ionone as well as high catalytic efficiency for the conversion of beta-ionone to dihydro-beta-ionone. It is the first report on the bioconversion of beta-ionone to dihydro-beta-ionone by using enoate reductase.