Ethanol yield and titer

An economically-attractive cellulosic technology almost certainly requires the strain to achieve ethanol yield, titer and rate higher than 90%, 40 g/L (5.1%v/v),1.0 g/L/h, respectively.

Trash Today, Ethanol Tomorrow

Major Advance In Biofuel Technology reported by ScienceDaily.

The bottleneck for cellulosic bioethanol commercilization

When talking about the bottleneck of cellulosic bioethanol commercialization, the 1st pop-up issues may be the technology of pretreatment, the efficiency of enzymatic hydrolysis, C5 microorganisms, etc. Another factor may be too much politics in this area. Too much talk, less action; too many talkers, not many real workers.....

Other than carbon dioxide from bioethanol car

It is known that bioethanol is a greener, sustainable and renewable fuel which helps to reduce the greenhouse gases that contribute to global warming. A 10% ethanol blends can reduce greenhouse gas emissions by 12-19%. The carbon dioxide's provenance is a crucial factor in this reduction. Other emissions concerned are nitrogen oxides, particles, and hydrocarbons, which are also lower lowered when you run a car on bioethanol. Modern gasoline cars are already so clean that these improvements are of marginal importance. But the improvements are significant for diesel cars. The only measurable emission that increases with alcohols is aldehydes. With current catalysers, the level is so low that this is negligible.

Market demand drives cellulosic ethanol investment

The fate of cellulosic ethanol industry will be decided by current and future market demand. Jeff Broin, the CEO of Poet predicted, "Within 20 years, US ethanol producers will churn out 135 billion gallons of ethanol a year, two-thirds of which will be cellulosic ethanol. That would make the domestic ethanol industry the nation's largest source of liquid transportation fuel." Today, the annual US gasoline market is 140 billion gallons. Therefore, there is a great market demand potential, which are attracting continued investment in and development of future ethanol technology with the government's policy and financial support.

However, many investors are wondering how long the technology can be commercialized and when the cellulosic ethanol industry will be profitable?

A list of people and organizations working on microorganisms to convert C5 sugars to ethanol

Here is a list of people and organizations working on microorganisms to convert C5 sugars to ethanol:

1. Thomas W. Jeffries, Director of Institute for Microbial and Biochemical Technology, USDA
Microorganism: Pichia stipitis
Description of research: Xylose fermentation; Metabolic regulation; Metabolic engineering; Yeast genetics; Depolymerization of cellulosic and hemicellulosic polysaccharides; Lignin biodegradation; Bioprocess engineering; Microbial strain selection and development; Regulation of heterologous enzymes; Overproduction of primary and secondary metabolites; Overproduction of extracellular enzymes; Microbial physiology.

Novozymes used the strain provided by Thomas Jeffries to ferment the mixture of glucose and xylose.

2. Nancy W. Y. Ho, Research Molecular Biologist/Group Leader, Laboratory of Renewable Resources Engineering, Purdue University
Microorganism: Saccharomyces cerevisiae 259ST. A genetically modified version of 259A capable of xylose fermentation due to insertion of xylose reductase and xylitol dehydrogenase genes from P. stipitis and overexpression of xylulokinase.

Iogen used the engineered yeast developed by Dr. Ho to produce ethanol from wheat straw.UBC and Tembec Chemicals Products have tested 259ST yeast on fermenting spent sulfite pulping liquor (SSL).

3. Lonnie O. Ingram ,Distinguished Professor, Director, Florida Center for Renewable Chemicals and Fuels (FCRC),Department of Microbiology and Cell Science University of Florida.
Microorganism: Escherichia coli
General areas: Global redirection of central metabolism by genetic engineering; Industrial fermentation processes; Carbohydrate metabolism; Expression and secretion of glycohydrolases which degrade plant polymers; Alcohol tolerance

4. Lisbeth Olsson, Professor, DTU Biosys, Department of Systems Biology,Technical University of Denmark, Center for Microbial Biotechnology, BioCentrum-DTU
Microorganism: Saccharomyces cerevisiae strains (F12, CR4, and CB4)
Article abstract: Fermentations with three different xylose-utilizing recombinant Saccharomyces cerevisiae strains (F12, CR4, and CB4) were performed using two different wheat hemicellulose substrates, unfermented starch free fibers, and an industrial ethanol fermentation residue, vinasse. With CR4 and F12, the maximum ethanol concentrations obtained were 4.3 and 4 g/L, respectively, but F12 converted xylose 15% faster than CR4 during the first 24 h. The comparison of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) with F12 showed that the highest, maximum ethanol concentrations were obtained with SSF. In general, the volumetric ethanol productivity was initially, highest in the SHF, but the overall volumetric ethanol productivity ended up being maximal in the SSF, at 0.013 and 0.010 g/L.h, with starch free fibers and vinasse, respectively.

"Separate and Simultaneous enzymatic hydrolysis and fermentation of wheat hemicellulose with recombinant xylose utilizing Saccharomyces cerevisiae", Applied Biochemistry and Biotechnology, vol: 129-132, pages: 117-129, 2006
5. Taso, George, Laboratory of Renewable Resources Engineering, A. A. Potter Engineering Center, Purdue University
Microorganism: First using xylose isomerase and then yeast.
Article abstract:d-Xylulose, an intermediate of d-xylose catabolism, was observed to be fermentable to ethanol and carbon dioxide in a yield of greater than 80% by yeasts (including industrial bakers' yeast) under fermentative conditions. This conversion appears to be carried out by many types of yeast known for d-glucose fermentation. In some yeasts, xylitol, in addition to ethanol, was produced from d-xylulose. Fermenting yeasts are also able to produce ethanol from d-xylose when d-xylose isomerizing enzyme is present. The results indicate that ethanol could be produced from d-xylose in a yield of greater than 80% by a two-step process. First, d-xylose is converted to d-xylulose by xylose isomerase. d-Xylulose is then fermented to ethanol by yeasts.

"Production of Ethanol from d-Xylose by Using d-Xylose Isomerase and Yeasts", Appl Environ Microbiol. 1981 February; 41(2): 430–436.

6. Ronald Hector, Stephen Hughes and Xin Liang-Li, the research molecular biologists with the USDA's Agricultural Research Service.
Research: Optimizations of genes of commercial yeasts for production of fuel ethanol from hemicellulosic biomass are carried out to meet the rapidly expanding need for ethanol. These yeast strains will be used in cellulosic ethanol production.

7. Richard Bolin
US patent: 5372939: Combined enzyme: Schizosaccharoyces pombe, cellulase, .beta.-glucosidase, and xylose isomerase

8. Iogen, Recombinant yeasts (424A). The yeast strain was provided by Dr. Nancy Ho in Purdue University.

9. Xethanol, proceeding with a Cooperative Research and Development Agreeement (CRADA) with FPL to engineer genetically modified yeasts that will substantially increase fermentation time of such feedstocks such as xylose, to produce either ethanol or xylitol, a natural sweetener.

10. Lee R. Lynd, Chemical and Biochemical Engineering Program, Dartmouth College and CFO of Mascoma
Microorganism: Thermoanaerobacter thermosaccharolyticum HG-8.
Study the xylose-utilizing thermophiles, Thermoanaerobacterium saccharolyticum and Thermoanaerobacterium thermosaccharolyticum.

Mascoma’s research laboratories are now developing a new generation of microbes and processes for economical conversion of cellulosic feedstocks into ethanol.

11. Min Zhang, National Renewable Energy Laboratory, Applied Biological Sciences
Microorganism: Bacterium Zymomonas mobilis
The ethanol-producing bacterium Zymomonas mobilis was metabolically engineered to broaden its range of fermentable substrates to include the pentose sugar xylose. Two operons encoding xylose assimilation and pentose phosphate pathway enzymes were constructed and transformed into Z. mobilis in order to generate a strain that grew on xylose and efficiently fermented it to ethanol. This strain efficiently fermented both glucose and xylose, which is essential for economical conversion of lignocellulosic biomass to ethanol.
Metabolic Engineering of a Pentose Metabolism Pathway in Ethnologenic Z Mobilis. Science Vol. 267. 1995, pp. 240 - 243

12. VTT Technical Research Centre
Microorganism: Saccharomyces cerevisiae
They have studied recombinant Saccharomyces cerevisiae yeast metabolically engineered to utilise the pentose sugar xylose, and compared the gene expression profiles on xylose to glucose-metabolizing cells.

13. Jeffrey Tolan and R. K. Finn, School of Chemical Engineering, Cornell University
Microorganism: Erwinia chrysathemi
Fermentation of D-xylose and L-arabinose to ethanol by Erwinia chrysathemi, Appl. Envirom. Microbiol., 53(9): 2033-2038, 1987.

14. Alexander, M.A.; Chapman, T.W.;& Jeffries, T.W. Department of Chem. Eng. University of Wisconsin
Microorganism: Candida shehatae
Continuous xylose ferrmentation by Candida shehatae in a two-stage reactor. Applied biochemistry and biotechnology, v. 17:221-229, 1988

15. Satoshi Katahira1, Atsuko Mizuike, Hideki Fukuda1 and Akihiko Kondo, Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University,
Microorganism: Recombinant yeast strain
Ethanol fermentation from lignocellulosic hydrolysate by a recombinant xylose- and cellooligosaccharide-assimilating yeast strain. Applied Microbiology and biotechnology, v. 72(6):1136-1143, 2006

16. Yong-su Jin, University of Illinois
Microorganism: E. coli
Improvement of xylose fermentation by recombinant Saccharomycescerevisiae through systematic and combinatorial approaches is funded by EBI (Energy Biosciences Institute). EBI is a new research organization that will pursue basic and applied research in the area of cellulosic biofuels, enhanced oil recovery, microbially-enhanced fossil fuel processing and biosequestration.

17. Girishchandra Patel, Division of Biological Sciences,National research council of Canada
Microorganism: Bacteroides polypragmatus
Fermentation of xylose and hemicellulose hydrolysates by an ethanol-adapted culture of Bacteroides polypragmatus, Archives of Microbiology, 146(1):68-73, 1986

Fuel Ethanol: Beyound Ethanol

1. Fuel ethanol is not sold with zero water content. Fuel ethanol with less than 0.5 % water is considered “anhydrous ethanol” while ethanol with higher water contents is usually referred to as “hydrated ethanol”.

2. Denatured alcohol typically contains up to 1% water and other constituents (e.g. methanol). Denaturing is to add denaturants to alcohol in order to make it unfit for beverage or internal human medical use.

3. A parameter that is used in evaluation of fuel ethanol is the pHe as defined by ASTM D6423. Like pH used to measure the acidity of aqueous solutions, the pHe value is a measure of the acid strength of high ethanol content fuels (>70% v/v). The pH 7 is considered neutral for aqueous solutions, whereas a pHe value of 9.55 is the neutralization point for ethanol.

4. Ethanolic solutions have lower conductivity than water.

5.The oxygen solubility in ethanol is higher than that of water.

Bioethanol shippment

With more boethanol into the market, the issue of transporting ethanol will attract more attention.

In a short term, the shipments of ethanol to terminals can be handled mostly by tanker truck and rail tank car rather than pipelines. In the long term, can we ship the ethanol by pipeline as gasoline? If so, the following issues need to be aware of and solved:

1. Ethanol’s water affinity. Because of the high solubility of ethanol in water, water accumulation in pipelines is a normal occurrence, which may risks rendering ethanol unusable as a transportation fuel.
2. Corrosion. Ethanol-related corrosion problems can be caused ethanol behavior in the pipe. The typical one is stress corrosion cracking, which is very hard to detect. The main factors involve in the type of metal (carbon steel), physical environment (areas of stress concentration, near weld heat effect zone), chemical environment (Dissolved oxygen), and other minors. This damage may be accelerated at weld joints or “hard spots” where the steel metallurgy has been altered.

To address these issues, the technical feasibility is the first step; then significant investments in new and modified facilities and operational practices will be demanded.

What can we expect from yeast for bioethanol commercial production?

For biofuel production from biomass, we want to robust microorganisms. Yeast is a traditional one but we need a yeast that has the ability to ferment both C5 and C6 sugar and more product tolerance.


Many scientists cross the world have been taking efforts to engineer yeast that can improve the speed and efficiency of ethanol production, which is a critical component to economically making biofuels a significant part of energy supply.

The 1st aspect is to engineer the yeast to ferment both C6 and C5 sugars by genetic modification. One of the example is the "Purdue yeast" developed by Nancy Ho.

The 2nd aspect is to engineer the yeast that has high-ethanol-tolerance. The typical example is the one developed by by MIT scientists (see http://web.mit.edu/newsoffice/2006/biofuels.html).