Elevated β-carotene synthesis by the engineered with enhanced CrtY expression.

-carotene is a precursor of vitamin A and a dietary supplement for its antioxidant property. Producing -carotene by microbial fermentation has attracted much attention to consumers' preference for the natural product. In this study， an engineered photosynthetic Rhodobacter sphaeroides producing -carotene was constructed by the following strategies: Five different strengths of promoters were used to investigate the effect of the expression level of crtY on β-carotene content. It was found that PrrnB increased β-carotene content by 109%. Blocking of the branched pentose phosphate pathway by zwf deletion， and 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 DCW among all 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.