â-Carotene is a precursor of vitamin A and a dietary supplement for its antioxidant property. Producing â-carotene by microbial fermentation has attracted much attention owing to consumers' preference for the natural product. In this study, an engineered photosynthetic Rhodobacter sphaeroides producing â-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 â-carotene content. It was found that PrrnB increased the â-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 â-carotene content of 14.93 mg/g dry cell weight (DCW) among all of the reported photosynthetic bacteria and the â-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 â-carotene.
Bacterial Proteins Fermentation