High-cell-density fermentation and pilot-scale biocatalytic studies of an engineered yeast expressing the heterologous glycoside hydrolase of 7-β-xylosyltaxanes.

The glycoside hydrolase of 7-β-xylosyltaxanes (designated as LXYL-P1-2) is encoded by Lxyl-p1-2 isolated from Lentinula edodes. This hydrolase specifically removes C-7 xylose from 7-β-xylosyltaxanes to form 7-β-hydroxyltaxanes, which can be used for the semi-synthesis of paclitaxel or its analogues. In our present study, we established a high-cell-density fermentation of the recombinant Pichia pastoris harboring the Lxyl-p1-2 gene. Moreover, we further optimized the fermentation conditions, including the initial cell density and the dissolved oxygen level in the induction phase. Under optimized conditions, the biomass of 312.3 g/l (wet cell weight, WCW) was obtained, and the biomass activity of the recombinant enzyme reached 6.55 × 10(4) U/g (WCW). The freeze-dried cells (32 g/l) were used to convert 7-β-xylosyltaxanes (10 g/l, 7-β-xylosyl-10-deacetyltaxol = 62.12 %) in a 5-l reaction volume, and a bioconversion rate about 80 % was achieved. The product purification was performed by ethyl acetate, silica gel chromatography, and preparative HPLC (prep-HPLC), yielding 15.13 g of 10-deacetyltaxol, 3.07 g of 10-deacetylcephalomanine, and 3.47 g of 10-deacetyltaxol C, respectively. In addition, the average recovery rate was around 70 %. Our work provided a foundation for the industrial utilization of the recombinant enzyme on the semi-synthesis of paclitaxel using 7-β-xylosyltaxanes.