LAUSR

Abstract In Rhodobacter sphaeroides, synthesis of coenzyme Q10 (CoQ10) shares the same precursor geranylgeranyl diphosphate (GGPP) with carotenoids. Therefore, suppression of carotenoids synthesis is supposed to pose positive effects on accumulation of CoQ10. In this paper, the carotenogenesis pathway was repressed using two different strategies, deletion of carotenogenic genes and overexpression of ppsR, a transcriptional regulator for photosynthesis genes, respectively. Knockout of carotenoids synthesis (crt) genes resulted in undetectable carotenoids as expected. However, the production of CoQ10 and biomass were both decreased to half as compared to the wild-type strain. In contrast, upon overexpression of ppsR, the production of carotenoids was decreased from 15.7 mg/L to 2.2 mg/L, and the CoQ10 production and content were enhanced by 28% and 34.2%, respectively. To further enhance the production of CoQ10, crtE was constitutively co-overexpressed with ppsR to improve the supply of GGPP as a key precursor for the isoprenoid side chain of CoQ10. The CoQ10 production and content of the resulting strain RspPE were increased to 73.2 mg/L and 5.67 mg/g, respectively, representing 47% and 55% improvement as compared to the wild type. This result demonstrated that appropriate reduction of carotenoids rather than complete blocking could enhance the CoQ10 production in Rhodobacter. sphaeroides.