A novel thermophilic β-carotene 15,15'-monooxygenase with broad substrate specificity from the marine bacterium Candidatus Pelagibacter sp. HTCC7211.

To characterize a novel thermophilic β-carotene 15,15'-monooxygenase BCMO isolated from the marine bacterium Candidatus Pelagibacter sp. HTCC7211. BCMO was functionally overexpressed in Escherichia coli and purified to homogeneity by Ni-NTA affinity chromatography and Superdex-200 gel filtration chromatography. Labeling experiments with HO demonstrated that the oxygen atom in the terminal aldehyde group of the produced retinal molecules was provided from both molecular oxygen and water, indicating that BCMO is the first characterized bacterial β-carotene 15,15'-monooxygenase. BCMO exhibited broad carotenoid substrate specificity toward α-carotene, β-cryptoxanthin, β-carotene, zeaxanthin, and lutein. The optimum temperature, pH, and concentrations of the substrate and enzyme for retinal production were 60 °C, 9.0, 500 mg β-carotene/L, and 2.5 U/ml, respectively. Under optimum conditions, 888.3 mg/L retinal was produced in 60 min with a conversion rate of 89.0% (w/w). BCMO is a potential candidate for the enzymatic synthesis of retinal in biotechnological applications.