scholarly journals Decreased Xylitol Formation during Xylose Fermentation in Saccharomyces cerevisiae Due to Overexpression of Water-Forming NADH Oxidase

2011 ◽  
Vol 78 (4) ◽  
pp. 1081-1086 ◽  
Author(s):  
Guo-Chang Zhang ◽  
Jing-Jing Liu ◽  
Wen-Tao Ding
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Xylose Fermentation ◽  
Nadh Oxidase ◽  
Xylose Reductase ◽  
Control Strain ◽  
Content Type ◽  
Ethanol Yields ◽  
Glycerol Yield ◽  
Set Up ◽  
And Control

ABSTRACTThe recombinant xylose-fermentingSaccharomyces cerevisiaestrain harboring xylose reductase (XR) and xylitol dehydrogenase (XDH) fromScheffersomyces stipitisrequires NADPH and NAD+, creates cofactor imbalance, and causes xylitol accumulation during growth ond-xylose. To solve this problem,noxE, encoding a water-forming NADH oxidase fromLactococcus lactisdriven by thePGK1promoter, was introduced into the xylose-utilizing yeast strain KAM-3X. A cofactor microcycle was set up between the utilization of NAD+by XDH and the formation of NAD+by water-forming NADH oxidase. Overexpression ofnoxEsignificantly decreased xylitol formation and increased final ethanol production during xylose fermentation. Under xylose fermentation conditions with an initiald-xylose concentration of 50 g/liter, the xylitol yields for of KAM-3X(pPGK1-noxE) and control strain KAM-3X were 0.058 g/g xylose and 0.191 g/g, respectively, which showed a 69.63% decrease owing tonoxEoverexpression; the ethanol yields were 0.294 g/g for KAM-3X(pPGK1-noxE) and 0.211 g/g for the control strain KAM-3X, which indicated a 39.33% increase due tonoxEoverexpression. At the same time, the glycerol yield also was reduced by 53.85% on account of the decrease in the NADH pool caused by overexpression ofnoxE.

scholarly journals Deletion ofFPS1, Encoding Aquaglyceroporin Fps1p, Improves Xylose Fermentation by Engineered Saccharomyces cerevisiae

2013 ◽  
Vol 79 (10) ◽  
pp. 3193-3201 ◽  
Author(s):  
Na Wei ◽  
Haiqing Xu ◽  
Soo Rin Kim ◽  
Yong-Su Jin
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Xylose Fermentation ◽  
Plant Biomass ◽  
Ethanol Yield ◽  
Xylose Reductase ◽  
Enzymatic Reactions ◽  
Xylose Metabolism ◽  
Xylose Consumption ◽  
Content Type ◽  
Ethanol Yields

ABSTRACTAccumulation of xylitol in xylose fermentation with engineeredSaccharomyces cerevisiaepresents a major problem that hampers economically feasible production of biofuels from cellulosic plant biomass. In particular, substantial production of xylitol due to unbalanced redox cofactor usage by xylose reductase (XR) and xylitol dehydrogenase (XDH) leads to low yields of ethanol. While previous research focused on manipulating intracellular enzymatic reactions to improve xylose metabolism, this study demonstrated a new strategy to reduce xylitol formation and increase carbon flux toward target products by controlling the process of xylitol secretion. Using xylitol-producingS. cerevisiaestrains expressing XR only, we determined the role of aquaglyceroporin Fps1p in xylitol export by characterizing extracellular and intracellular xylitol. In addition, whenFPS1was deleted in a poorly xylose-fermenting strain with unbalanced XR and XDH activities, the xylitol yield was decreased by 71% and the ethanol yield was substantially increased by nearly four times. Experiments with our optimized xylose-fermenting strain also showed thatFPS1deletion reduced xylitol production by 21% to 30% and increased ethanol yields by 3% to 10% under various fermentation conditions. Deletion ofFPS1decreased the xylose consumption rate under anaerobic conditions, but the effect was not significant in fermentation at high cell density. Deletion ofFPS1resulted in higher intracellular xylitol concentrations but did not significantly change the intracellular NAD+/NADH ratio in xylose-fermenting strains. The results demonstrate that Fps1p is involved in xylitol export inS. cerevisiaeand present a new gene deletion target,FPS1, and a mechanism different from those previously reported to engineer yeast for improved xylose fermentation.

Guidance and control algorithms for mini UAV autopilots

2017 ◽  
Vol 89 (1) ◽  
pp. 133-144 ◽  
Author(s):  
Elisa Capello ◽  
Giorgio Guglieri ◽  
Gianluca Ristorto
Keyword(s):  
Attitude Control ◽  
Path Following ◽  
Adaptive Controller ◽  
Computationally Efficient ◽  
Control Laws ◽  
Content Type ◽  
Guidance And Control ◽  
Aerial Vehicle ◽  
Set Up ◽  
And Control

Purpose The aim of this paper is the implementation and validation of control and guidance algorithms for unmanned aerial vehicle (UAV) autopilots. Design/methodology/approach The path-following control of the UAV can be separated into different layers: inner loop for pitch and roll attitude control, outer loop on heading, altitude and airspeed control for the waypoints tracking and waypoint navigation. Two control laws are defined: one based on proportional integrative derivative (PID) controllers both for inner and outer loops and one based on the combination of PIDs and an adaptive controller. Findings Good results can be obtained in terms of trajectory tracking (based on waypoints) and of parameter variations. The adaptive control law guarantees smoothing responses and less oscillations and glitches on the control deflections. Practical implications The proposed controllers are easily implementable on-board and are computationally efficient. Originality/value The algorithm validation via hardware in the loop simulations can be used to reduce the platform set-up time and the risk of losing the prototype during the flight tests.

scholarly journals Metabolic Engineering of a Phosphoketolase Pathway for Pentose Catabolism in Saccharomyces cerevisiae

2004 ◽  
Vol 70 (5) ◽  
pp. 2892-2897 ◽  
Author(s):  
Marco Sonderegger ◽  
Michael Schümperli ◽  
Uwe Sauer
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Plant Material ◽  
Xylose Fermentation ◽  
Ethanol Yield ◽  
Limited Capacity ◽  
Fermentation Rate ◽  
Phosphoketolase Pathway ◽  
Ethanol Yields ◽  
Acetate Accumulation ◽  
Acetate Formation

ABSTRACT Low ethanol yields on xylose hamper economically viable ethanol production from hemicellulose-rich plant material with Saccharomyces cerevisiae. A major obstacle is the limited capacity of yeast for anaerobic reoxidation of NADH. Net reoxidation of NADH could potentially be achieved by channeling carbon fluxes through a recombinant phosphoketolase pathway. By heterologous expression of phosphotransacetylase and acetaldehyde dehydrogenase in combination with the native phosphoketolase, we installed a functional phosphoketolase pathway in the xylose-fermenting Saccharomyces cerevisiae strain TMB3001c. Consequently the ethanol yield was increased by 25% because less of the by-product xylitol was formed. The flux through the recombinant phosphoketolase pathway was about 30% of the optimum flux that would be required to completely eliminate xylitol and glycerol accumulation. Further overexpression of phosphoketolase, however, increased acetate accumulation and reduced the fermentation rate. By combining the phosphoketolase pathway with the ald6 mutation, which reduced acetate formation, a strain with an ethanol yield 20% higher and a xylose fermentation rate 40% higher than those of its parent was engineered.

scholarly journals Anaerobic Xylose Fermentation by Recombinant Saccharomyces cerevisiae Carrying XYL1, XYL2, andXKS1 in Mineral Medium Chemostat Cultures

2000 ◽  
Vol 66 (8) ◽  
pp. 3381-3386 ◽  
Author(s):  
Anna Eliasson ◽  
Camilla Christensson ◽  
C. Fredrik Wahlbom ◽  
Bärbel Hahn-Hägerdal
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Ethanol Yield ◽  
Xylose Reductase ◽  
Dry Weight ◽  
Pichia Stipitis ◽  
Feed Ratio ◽  
Gene Encoding ◽  
Chemostat Cultures ◽  
Glucose Ratio ◽  
Ethanol Yields

ABSTRACT For ethanol production from lignocellulose, the fermentation of xylose is an economic necessity. Saccharomyces cerevisiaehas been metabolically engineered with a xylose-utilizing pathway. However, the high ethanol yield and productivity seen with glucose have not yet been achieved. To quantitatively analyze metabolic fluxes in recombinant S. cerevisiae during metabolism of xylose-glucose mixtures, we constructed a stable xylose-utilizing recombinant strain, TMB 3001. The XYL1 and XYL2genes from Pichia stipitis, encoding xylose reductase (XR) and xylitol dehydrogenase (XDH), respectively, and the endogenousXKS1 gene, encoding xylulokinase (XK), under control of thePGK1 promoter were integrated into the chromosomalHIS3 locus of S. cerevisiae CEN.PK 113-7A. The strain expressed XR, XDH, and XK activities of 0.4 to 0.5, 2.7 to 3.4, and 1.5 to 1.7 U/mg, respectively, and was stable for more than 40 generations in continuous fermentations. Anaerobic ethanol formation from xylose by recombinant S. cerevisiae was demonstrated for the first time. However, the strain grew on xylose only in the presence of oxygen. Ethanol yields of 0.45 to 0.50 mmol of C/mmol of C (0.35 to 0.38 g/g) and productivities of 9.7 to 13.2 mmol of C h−1 g (dry weight) of cells−1 (0.24 to 0.30 g h−1 g [dry weight] of cells−1) were obtained from xylose-glucose mixtures in anaerobic chemostat cultures, with a dilution rate of 0.06 h−1. The anaerobic ethanol yield on xylose was estimated at 0.27 mol of C/(mol of C of xylose) (0.21 g/g), assuming a constant ethanol yield on glucose. The xylose uptake rate increased with increasing xylose concentration in the feed, from 3.3 mmol of C h−1 g (dry weight) of cells−1 when the xylose-to-glucose ratio in the feed was 1:3 to 6.8 mmol of C h−1 g (dry weight) of cells−1 when the feed ratio was 3:1. With a feed content of 15 g of xylose/liter and 5 g of glucose/liter, the xylose flux was 2.2 times lower than the glucose flux, indicating that transport limits the xylose flux.

scholarly journals Adjustment of Trehalose Metabolism in Wine Saccharomyces cerevisiae Strains To Modify Ethanol Yields

2013 ◽  
Vol 79 (17) ◽  
pp. 5197-5207 ◽  
Author(s):  
D. Rossouw ◽  
E. H. Heyns ◽  
M. E. Setati ◽  
S. Bosch ◽  
F. F. Bauer
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Genetic Modification ◽  
Target Genes ◽  
Tca Cycle ◽  
Pentose Phosphate ◽  
Systematic Screening ◽  
Content Type ◽  
Genes Encoding ◽  
Ethanol Yields ◽  
Trehalose Biosynthesis

ABSTRACTThe ability ofSaccharomyces cerevisiaeto efficiently produce high levels of ethanol through glycolysis has been the focus of much scientific and industrial activity. Despite the accumulated knowledge regarding glycolysis, the modification of flux through this pathway to modify ethanol yields has proved difficult. Here, we report on the systematic screening of 66 strains with deletion mutations of genes encoding enzymes involved in central carbohydrate metabolism for altered ethanol yields. Five of these strains showing the most prominent changes in carbon flux were selected for further investigation. The genes were representative of trehalose biosynthesis (TPS1, encoding trehalose-6-phosphate synthase), central glycolysis (TDH3, encoding glyceraldehyde-3-phosphate dehydrogenase), the oxidative pentose phosphate pathway (ZWF1, encoding glucose-6-phosphate dehydrogenase), and the tricarboxylic acid (TCA) cycle (ACO1andACO2, encoding aconitase isoforms 1 and 2). Two strains exhibited lower ethanol yields than the wild type (tps1Δ andtdh3Δ), while the remaining three showed higher ethanol yields. To validate these findings in an industrial yeast strain, theTPS1gene was selected as a good candidate for genetic modification to alter flux to ethanol during alcoholic fermentation in wine. Using low-strength promoters active at different stages of fermentation, the expression of theTPS1gene was slightly upregulated, resulting in a decrease in ethanol production and an increase in trehalose biosynthesis during fermentation. Thus, the mutant screening approach was successful in terms of identifying target genes for genetic modification in commercial yeast strains with the aim of producing lower-ethanol wines.

scholarly journals Increasing Anaerobic Acetate Consumption and Ethanol Yields in Saccharomyces cerevisiae with NADPH-Specific Alcohol Dehydrogenase

2015 ◽  
Vol 81 (23) ◽  
pp. 8108-8117 ◽  
Author(s):  
Brooks M. Henningsen ◽  
Shuen Hon ◽  
Sean F. Covalla ◽  
Carolina Sonu ◽  
D. Aaron Argyros ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Alcohol Dehydrogenase ◽  
Ethanol Yield ◽  
Pentose Phosphate ◽  
Wild Type ◽  
Bifidobacterium Adolescentis ◽  
Acetaldehyde Dehydrogenase ◽  
Content Type ◽  
Sugar Fermentation ◽  
Ethanol Yields

ABSTRACTSaccharomyces cerevisiaehas recently been engineered to use acetate, a primary inhibitor in lignocellulosic hydrolysates, as a cosubstrate during anaerobic ethanolic fermentation. However, the original metabolic pathway devised to convert acetate to ethanol uses NADH-specific acetylating acetaldehyde dehydrogenase and alcohol dehydrogenase and quickly becomes constrained by limited NADH availability, even when glycerol formation is abolished. We present alcohol dehydrogenase as a novel target for anaerobic redox engineering ofS. cerevisiae. Introduction of an NADPH-specific alcohol dehydrogenase (NADPH-ADH) not only reduces the NADH demand of the acetate-to-ethanol pathway but also allows the cell to effectively exchange NADPH for NADH during sugar fermentation. Unlike NADH, NADPH can be freely generated under anoxic conditions, via the oxidative pentose phosphate pathway. We show that an industrial bioethanol strain engineered with the original pathway (expressing acetylating acetaldehyde dehydrogenase fromBifidobacterium adolescentisand with deletions of glycerol-3-phosphate dehydrogenase genesGPD1andGPD2) consumed 1.9 g liter−1acetate during fermentation of 114 g liter−1glucose. Combined with a decrease in glycerol production from 4.0 to 0.1 g liter−1, this increased the ethanol yield by 4% over that for the wild type. We provide evidence that acetate consumption in this strain is indeed limited by NADH availability. By introducing an NADPH-ADH fromEntamoeba histolyticaand with overexpression ofACS2andZWF1, we increased acetate consumption to 5.3 g liter−1and raised the ethanol yield to 7% above the wild-type level.

scholarly journals Shuffling of Promoters for Multiple Genes To Optimize Xylose Fermentation in an Engineered Saccharomyces cerevisiae Strain

2007 ◽  
Vol 73 (19) ◽  
pp. 6072-6077 ◽  
Author(s):  
Chenfeng Lu ◽  
Thomas Jeffries
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Ethanol Production ◽  
Xylose Fermentation ◽  
Xylose Reductase ◽  
Gene Promoter ◽  
Expression Levels ◽  
Multiple Genes ◽  
Expression Of Genes ◽  
Xylulose Kinase ◽  
Engineered Saccharomyces Cerevisiae

ABSTRACT We describe here a useful metabolic engineering tool, multiple-gene-promoter shuffling (MGPS), to optimize expression levels for multiple genes. This method approaches an optimized gene overexpression level by fusing promoters of various strengths to genes of interest for a particular pathway. Selection of these promoters is based on the expression levels of the native genes under the same physiological conditions intended for the application. MGPS was implemented in a yeast xylose fermentation mixture by shuffling the promoters for GND2 and HXK2 with the genes for transaldolase (TAL1), transketolase (TKL1), and pyruvate kinase (PYK1) in the Saccharomyces cerevisiae strain FPL-YSX3. This host strain has integrated xylose-metabolizing genes, including xylose reductase, xylitol dehydrogenase, and xylulose kinase. The optimal expression levels for TAL1, TKL1, and PYK1 were identified by analysis of volumetric ethanol production by transformed cells. We found the optimal combination for ethanol production to be GND2-TAL1-HXK2-TKL1-HXK2-PYK1. The MGPS method could easily be adapted for other eukaryotic and prokaryotic organisms to optimize expression of genes for industrial fermentation.

Sign in / Sign up

Export Citation Format

Share Document