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β-Carotene is a precursor of vitamin A and a dietary supplement for its antioxidant property. Producing βcarotene by microbial fermentation has attracted much attention owing to consumers' preference for the natural product. In this study, an engineered photosynthetic Rhodobacter sphaeroides producing β-carotene was constructed by the following strategies:(1) five promoters of different strengths were used to investigate the effect of the expression level of crtY on β-carotene content. It was found that P rrnB increased the β-carotene content by 109%. (2) blocking of the branched pentose phosphate pathway by zwf deletion, and (3) overexpressing dxs could restore the transcriptional levels of crtE and crtB. Finally, the engineered RS-C3 has the highest β-carotene content of 14.93 mg/g dry cell weight (DCW) among all of the reported photosynthetic bacteria and the β-carotene content reached 3.34 mg/g DCW under light conditions. Our results will be available for industrial use to supply a large quantity of natural β-carotene.

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