Related Experiment Video
Updated: Jul 11, 2026
14:53
Techniques for the Evolution of Robust Pentose-fermenting Yeast for Bioconversion of Lignocellulose to Ethanol
Published on: October 24, 2016
Metabolic engineering for improved fermentation of pentoses by yeasts
1USDA Forest Service, Forest Products Laboratory, Madison, WI 53726-2398, USA. twjeffries@fs.fed.us
Applied Microbiology and Biotechnology
|November 5, 2003
Summary
Researchers engineered yeast to ferment xylose, a key sugar from plant matter. This advance enables efficient bioconversion of lignocellulose into biofuels and chemicals.
Area of Science:
- Biotechnology
- Metabolic Engineering
- Yeast Fermentation
Background:
- Lignocellulose bioconversion to fuels and chemicals requires efficient xylose fermentation.
- Wild-type Saccharomyces cerevisiae cannot metabolize xylose, necessitating genetic engineering.
- Understanding xylose uptake and metabolism pathways is crucial for improving yeast strains.
Purpose of the Study:
- To engineer xylose metabolism in Saccharomyces cerevisiae for lignocellulose bioconversion.
- To identify strategies for balancing cofactor supply (NAD(P)/NAD(P)H) during xylose fermentation.
- To optimize yeast strains for enhanced ethanol production from xylose.
Main Methods:
- Over-expression of aldose reductase, xylitol dehydrogenase, and xylulokinase genes.
- Manipulation of the oxidative pentose phosphate pathway to reduce NADPH production.
- Investigation of respiration's role in xylose utilization and ethanol yield.
- Engineering of arabinose metabolism pathways in S. cerevisiae.
Main Results:
- Engineered S. cerevisiae strains can assimilate and ferment xylose.
- Balanced NAD(P)/NAD(P)H supply is critical to prevent xylitol accumulation.
- Reducing respiration capacity in xylose-metabolizing yeasts increases ethanol production.
- Adapted Pichia stipitis strains achieved ethanol yields of 0.45 g/g sugar.
Conclusions:
- Genetic engineering enables S. cerevisiae to ferment xylose, crucial for lignocellulose valorization.
- Metabolic balancing and pathway optimization are key to efficient xylose fermentation.
- Commercialization of yeast-based lignocellulose bioconversion appears feasible for specific applications.
Related Concept Videos
01:29Fermentation
Most eukaryotic organisms require oxygen to survive and function adequately. Such organisms produce large amounts of energy during aerobic respiration by metabolizing glucose and oxygen into carbon dioxide and water. However, most eukaryotes can generate some energy in the absence of oxygen by anaerobic metabolism.
Fermentation is a type of metabolic process that occurs in the absence of oxygen, where organic molecules such as glucose are broken down to produce energy. During this process, the...
Fermentation is a type of metabolic process that occurs in the absence of oxygen, where organic molecules such as glucose are broken down to produce energy. During this process, the...
01:20Fates of Pyruvate
Pyruvate is the end product of glycolysis, where glucose is oxidized to pyruvate, simultaneously reducing NAD+ to NADH. Two molecules of ATP are also produced by substrate-level phosphorylation.
In aerobic organisms, pyruvate is metabolized via the citric acid cycle to produce reduced coenzymes NADH and FADH2. These coenzymes are then oxidized in the electron transport chain to produce ATP and, in the process, regenerate the NAD+ and FAD. As seen in some cell types and organisms, fermentation...
In aerobic organisms, pyruvate is metabolized via the citric acid cycle to produce reduced coenzymes NADH and FADH2. These coenzymes are then oxidized in the electron transport chain to produce ATP and, in the process, regenerate the NAD+ and FAD. As seen in some cell types and organisms, fermentation...
01:24Other Glycolytic Pathways
The pentose phosphate pathway (PPP) operates in parallel with glycolysis, facilitating the metabolism of both pentoses and glucose. This pathway consists of two distinct phases: the oxidative and non-oxidative phases. While it does not directly generate ATP, the intermediates formed during the process can integrate into glycolysis, contributing to cellular energy metabolism when required.Oxidative Phase: NADPH ProductionThe oxidative phase of the pentose phosphate pathway is primarily...
01:23Microbial Fermentation
Fermentation is a crucial anaerobic metabolic process that enables microbes to derive energy from sugar without relying on oxygen or an electron transport chain. This process is fundamental to various biological and industrial applications and is classified based on the metabolic products generated.Role of Pyruvate in FermentationPyruvate and its derivatives serve as key electron acceptors in fermentative pathways. The oxidation of NADH to regenerate NAD+ is essential for the continuation of...
01:22Bioreactor Controls-III
Strain improvement is a foundational strategy in industrial microbiology aimed at maximizing microbial productivity, particularly because natural isolates typically yield commercially valuable products in very low concentrations. Although optimizing the culture medium and environmental conditions can improve yields, these adjustments are inherently limited by the organism’s genetic potential. As a result, the focus shifts toward genetic modifications to enhance biosynthetic capacity. The...
01:27Production of Alcohol
Continuous fermentation is a key strategy in industrial ethanol production, particularly when efficiency, scalability, and high yields are essential. This approach allows for uninterrupted operation and optimized resource utilization. The primary feedstock, corn starch, undergoes enzymatic hydrolysis facilitated by α-amylase and glucoamylase. These enzymes break down the starch into fermentable sugars such as glucose, which are readily assimilated by fermentative microorganisms.Fermentation...