Fanglong Zhao

Optimization of a cytochrome P450 oxidation system for enhancing protopanaxadiol production in Saccharomyces cerevisiae.

Ginsenosides, the major bioactive components of Panax ginseng, are regarded as promising high‐value pharmaceutical compounds. In ginseng, ginsenosides are produced from their precursor protopanaxadiol. Recently, an artificial biosynthetic pathway of protopanaxadiol was built in Saccharomyces cerevisiae by introducing a P. ginseng dammarenediol‐II synthase, a P. ginseng cytochrome P450‐type protopanaxadiol synthase (PPDS), and a Arabidopsis thaliana NADPH‐cytochrome P450 reductase (ATR1). In this engineered yeast strain, however, the low metabolic flux through PPDS resulted in a low productivity of protopanaxadiol. Moreover, health of the yeast cells was significantly affected by reactive oxygen species released by the pool coupling between PPDS and ATR1. To overcome the obstacles in protopanaxadiol production, PPDS was modified through transmembrane domain truncation and self‐sufficient PPDS–ATR1 fusion construction in this study. The fusion enzymes conferred approximately 4.5‐fold increase in catalytic activity, and 71.1% increase in protopanaxadiol production compared with PPDS and ATR1 co‐expression. Our in vivo experiment indicated that the engineered yeast carrying fusion protein effectively converted 96.8% of dammarenediol‐II into protopanaxadiol. Protopanaxadiol production in a 5 L bioreactor in fed‐batch fermentation reached 1436.6 mg/L. Our study not only improved protopanaxadiol production in yeast, but also provided a generic method to improve activities of plant cytochrome P450 monooxygenases. This method is promising to be applied to other P450 systems in yeast. Biotechnol. Bioeng. 2016;113: 1787–1795.

Suitable extracellular oxidoreduction potential inhibit rex regulation and effect central carbon and energy metabolism in Saccharopolyspora spinosa

BackgroundPolyketides, such as spinosad, are mainly synthesized in the stationary phase of the fermentation. The synthesis of these compounds requires many primary metabolites, such as acetyl-CoA, propinyl-CoA, NADPH, and succinyl-CoA. Their synthesis is also significantly influenced by NADH/NAD+. Rex is the sensor of NADH/NAD+ redox state, whose structure is under the control of NADH/NAD+ ratio. The structure of rex controls the expression of many NADH dehydrogenases genes and cytochrome bd genes. Intracellular redox state can be influenced by adding extracellular electron acceptor H2O2. The effect of extracellular oxidoreduction potential on spinosad production has not been studied. Although extracellular oxidoreduction potential is an important environment effect in polyketides production, it has always been overlooked. Thus, it is important to study the effect of extracellular oxidoreduction potential on Saccharopolyspora spinosa growth and spinosad production.ResultsDuring stationary phase, S. spinosa was cultured under oxidative (H2O2) and reductive (dithiothreitol) conditions. The results show that the yield of spinosad and pseudoaglycone increased 3.11 fold under oxidative condition. As H2O2 can be served as extracellular electron acceptor, the ratios of NADH/NAD+ were measured. We found that the ratio of NADH/NAD+ under oxidative condition was much lower than that in the control group. The expression of cytA and cytB in the rex mutant indicated that the expression of these two genes was controlled by rex, and it was not activated under oxidative condition. Enzyme activities of PFK, ICDH, and G6PDH and metabolites results indicated that more metabolic flux flow through spinosad synthesis.ConclusionThe regulation function of rex was inhibited by adding extracellular electron acceptor-H2O2 in the stationary phase. Under this condition, many NADH dehydrogenases which were used to balance NADH/NAD+ by converting useful metabolites to useless metabolites and unefficient terminal oxidases (cytochrome bd) were not expressed. So lots of metabolites were not waste to balance. As a result, un-wasted metabolites related to spinosad and PSA synthesis resulted in a high production of spinosad and PSA under oxidative condition.

Enhancing Saccharomyces cerevisiae reactive oxygen species and ethanol stress tolerance for high-level production of protopanoxadiol

Protopanaxadiol (PPD) is an active compound in Panax ginseng. Recently, an optimized PPD synthesis pathway contained a ROS releasing step (a P450-type PPD synthase, PPDS) was introduced into Saccharomyces cerevisiae. Here reported a synergistic effect of PPDS-CPR (CPR, cytochrome P450 reductase) uncoupling and ethanol stress on ROS releasing, which reduced cells viability. To build a robust strain, a cell wall integrity associated gene SSD1 was high-expressed to improve ethanol tolerance, and ROS level decreased for 24.7%. Then, regulating the expression of an oxidative stress regulation gene YBP1 decreased 75.2% of ROS releasing, and improved cells viability from 71.3±1.3% to 88.3±1.4% at 84h. Increased cells viability enables yeast to produce more PPD through feeding additional ethanol. In 5L fermenter, PPD production of W3a-ssPy reached to 4.25±0.18g/L (19.48±0.28mg/L/OD600), which is the highest yield reported so far. This work makes the industrial production of PPD possible by microbial fermentation.

Semicontinuous sophorolipid fermentation using a novel bioreactor with dual ventilation pipes and dual sieve‐plates coupled with a novel separation system

Sophorolipids (SLs) are biosurfactants with widespread applications. The yield and purity of SLs are two important factors to be considered during their commercial large‐scale production. Notably, SL accumulation causes an increase in viscosity, decrease in dissolved oxygen and product inhibition in the fermentation medium. This inhibits the further production and purification of SLs. This describes the development of a novel integrated system for SL production using Candida albicans O‐13‐1. Semicontinuous fermentation was performed using a novel bioreactor with dual ventilation pipes and dual sieve‐plates (DVDSB). SLs were separated and recovered using a newly designed two‐stage separation system. After SL recovery, the fermentation broth containing residual glucose and oleic acid was recycled back into the bioreactor. This novel approach considerably alleviated the problem of product inhibition and accelerated the rate of substrate utilization. Production of SLs achieved was 477 g l−1, while their productivity was 1.59 g l−1 h−1. Purity of SLs improved by 23.3%, from 60% to 74%, using DVDSB with the separation system. The conversion rate of carbon source increased from 0.5 g g−1 (in the batch fermentation) to 0.6 g g−1. These results indicated that the integrated system could improve the efficiency of production and purity of SLs.

Production of sesquiterpenoid zerumbone from metabolic engineered Saccharomyces cerevisiae

Zerumbone, the predominant sesquiterpenoid component of Zingiber zerumbet, exhibits diverse pharmacological properties. In this study, de novo production of zerumbone was achieved in a metabolically engineered yeast cell factory by introducing α-humulene synthase (ZSS1), α-humulene 8-hydroxylase (CYP71BA1) and zerumbone synthase variant (ZSD1S114A) from Z. zerumbet, together with AtCPR1 from Arabidopsis thaliana into the yeast strain. Multistep metabolic engineering strategies were applied, including the over-expression of the mevalonate (MVA) pathway rate-limiting enzymes tHMG1 and ERG20, regulation of ERG9 by an inducible promoter and competitive pathway deletion to redirect metabolic flux toward the desired product. In the engineered strain, α-humulene production increased by 18-fold, to 92 mg/L compared to that in the original strain. Five cytochrome P450 reductases (CPRs) from different sources were selected for CYP71BA1 adaptability tests, and AtCPR1 from A. thaliana was found to be the optimal, producing 113.16 μg/L of 8-hydroxy-α-humulene. Multicopy integration of CYP71BA1, AtCPR1, ZSS1 and ICE2 (type III membrane protein) genes resulting in strain LW14 increased the production of 8-hydroxy-α-humulene by 134-fold to 15.2 mg/L. Expressing ZSD1S114A in the ura3 site of strain LW14 resulted in the production of 7 mg/L zerumbone. Multicopy integration of ZSD1S114A increased the production of zerumbone to 20.6 mg/L. The high zerumbone-producing strain was used for batch and fed-batch fermentation in a 5-L bioreactor and zerumbone degradation by yeast was observed; the production of zerumbone finally reached 40 mg/L by fed-batch fermentation in a 5-L bioreactor.

Engineering Saccharomyces cerevisiae for enhanced production of protopanaxadiol with cofermentation of glucose and xylose

Protopanaxadiol (PPD), an active triterpene compound, is the precursor of high-value ginsenosides. In this study, we report a strategy for the enhancement of PPD production in Saccharomyces cerevisiae by cofermentation of glucose and xylose. In mixed sugar fermentation, strain GW6 showed higher PPD titer and yield than that obtained from glucose cultivation. Then, engineering strategies were implemented on GW6 to enhance the PPD yields, such as adjustment of the central carbon metabolism, optimization of the mevalonate pathway, reinforcement of the xylose assimilation pathway, and regulation of cofactor balance, namely, overexpression of xPK/PTA, ERG10/ERG12/ERG13, XYL1/XYL2/TAL1, and POS5, respectively. In particular, the final obtained strain GW10, harboring overexpressed POS5, exhibited the highest PPD yield, which was 2.06 mg of PPD/g of mixed sugar. In a 5-L fermenter, PPD titer reached 152.37 mg/L. These promising results demonstrate the great advantages of mixed sugar over glucose for high-yield production of PPD.