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

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To characterize a novel thermophilic β-carotene 15,15'-monooxygenase BCMO7211 isolated from the marine bacterium Candidatus Pelagibacter sp. HTCC7211. BCMO7211 was functionally overexpressed in Escherichia coli and purified to homogeneity by Ni-NTA affinity chromatography and Superdex-200 gel filtration chromatography. Labeling experiments with H218O 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 BCMO7211 is the first characterized bacterial β-carotene 15,15'-monooxygenase. BCMO7211 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, 500mg β-carotene/L, and 2.5 U/ml, respectively. Under optimum conditions, 888.3mg/L retinal was produced in 60min with a conversion rate of 89.0% (w/w). BCMO7211 is a potential candidate for the enzymatic synthesis of retinal in biotechnological applications.