Squalene is a strong antioxidant used extensively in the food, cosmetic and medicine industries. Rhodopseudomonas palustris TIE-1 was used as the host because of its ability to grow photosynthetically using solar energy and carbon dioxide from atmosphere. The deletion of the shc gene resulted in a squalene production of 3.8 mg/g DCW, which was 27-times higher than that in the wild type strain. For constructing a substrate channel to elevate the conversion efficiency, we tried to fuse crtE gene with hpnD gene. By fusing the two genes, squalene content was increased to 12.6 mg/g DCW, which was 27.4 % higher than that resulted from the co-expression method. At last, the titer of squalene reached 15.8 mg/g DCW by co-expressing the dxs gene, corresponding to 112-fold increase relative to that for wild-type strain. This study provided novel strategies for improving squalene yield and demonstrated the potential of producing squalene by Rhodopseudomonas palustris.
Coenzyme Q10 (CoQ10), a strong antioxidant, is used extensively in food, cosmetic and medicine industries. A natural producer, Rhodopseudomonas palustris, was engineered to overproduce CoQ10. For increasing the CoQ10 content, crtB gene was deleted to block the carotenoid pathway. crtB gene deletion led to 33% improvement of CoQ10 content over the wild type strain. However, it was found that the yield of hopanoids was also increased by competing for the precursors from carotenoid pathway with CoQ10 pathway. To further increase the CoQ10 content, hopanoid pathway was blocked by deleting shc gene, resulting in R. palustris [Δshc, ΔcrtB] to produce 4·7 mg g−1 DCW CoQ10, which was 1·2 times higher than the CoQ10 content in the wild type strain. The common strategy of co‐expression of rate‐limiting enzymes (DXS, DPS and UbiA) was combined with the pathway blocking method resulted in 8·2 mg g−1 DCW of CoQ10, which was 2·9 times higher than that of wild type strain. The results suggested a synergistic effect among different metabolic engineering strategies. This study demonstrates the potential of R. palustris for CoQ10 production and provides viable strategies to increase CoQ10 titer.
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