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Generally, the mixed acid fermentation of E. coli, which begins at the end of glycolysis, involves the production of lactate, acetate, formate, and ethanol from pyruvate [1]. | Generally, the mixed acid fermentation of E. coli, which begins at the end of glycolysis, involves the production of lactate, acetate, formate, and ethanol from pyruvate [1]. | ||
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Originally, acetaldehyde in E. coli is converted into ethanol by alcohol dehydrogenase E (adhE) [2]. Thus, to preserve acetaldehyde for dark fermentation, adhE was also knocked out. Acetaldehyde dehydrogenase was then inserted into the E. coli to convert acetaldehyde into acetyl-CoA. The process of converting acetaldehyde into acetyl-CoA produces 2 NADH and 2 hydrogen protons. In addition, the glycolytic pathway also produces 2 NADH and 2 hydrogen protons. Thus, an expected total 4 NADH and 4 hydrogen protons are produced from one mole of glucose. | Originally, acetaldehyde in E. coli is converted into ethanol by alcohol dehydrogenase E (adhE) [2]. Thus, to preserve acetaldehyde for dark fermentation, adhE was also knocked out. Acetaldehyde dehydrogenase was then inserted into the E. coli to convert acetaldehyde into acetyl-CoA. The process of converting acetaldehyde into acetyl-CoA produces 2 NADH and 2 hydrogen protons. In addition, the glycolytic pathway also produces 2 NADH and 2 hydrogen protons. Thus, an expected total 4 NADH and 4 hydrogen protons are produced from one mole of glucose. | ||
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NADH is used to convert ferredoxin from its oxidized state into its reduced state. This reaction is carried out by ferredoxin oxidoreductase, which is inserted into the bacteria. Ferredoxin then reduces hydrogen protons into hydrogen gas with hydrogenase. As a result of the process, ferredoxin is returned to its oxidized state, enabling the cycle to continue. | NADH is used to convert ferredoxin from its oxidized state into its reduced state. This reaction is carried out by ferredoxin oxidoreductase, which is inserted into the bacteria. Ferredoxin then reduces hydrogen protons into hydrogen gas with hydrogenase. As a result of the process, ferredoxin is returned to its oxidized state, enabling the cycle to continue. | ||
Revision as of 03:59, 3 October 2012
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Overall project
The use of microorganisms as a method to obtain hydrogen gas is well documented but there has yet to be a process which can produce the ideal ratio of glucose to hydrogen gas due to a variety of factors. With each method that has been created, only a select number of pathways are modified in order to produce the desired outcome but never close to the ideal 1:4 mole ratio between glucose and hydrogen gas.
With this as the central focus of our project we are planning to remove pathways involved in dark fermentation and adding an entirely new pathway in the hopes of giving our modified E.coli the ability to generate hydrogen gas as a by product. Furthermore, the new pathway can potentially allow better electron transfer efficiency, which can produce the required 1:4 ratio.
Project Idea
Proposed as the ultimate transport fuel, hydrogen holds great promise as an alternative energy source to conventional fossil fuels because it has the potential to eliminate many of the problems that fossil fuels create (Forsberg 2007). Since hydrogen is both a fuel and an energy carrier that can be efficiently converted into other energy carriers, it is especially viable for the fuel cell-based economy in coming years (Jensen et al 2011). However, most hydrogen gas is currently produced using thermochemical reformation of fossil fuels, which results in carbon dioxide waste products (Spormann et al 2005). This major drawback of the current process prevents hydrogen from being considered a truly clean energy source. To avoid the emission of greenhouse gases, the hydrogen source needs to be renewable and carbon-neutral. Biohydrogen production, which is instead catalyzed by microorganisms, presents an attractive and environmentally-friendly conversion of hydrogen energy for the future (Lee et al 2011).
While biohydrogen production is still in its early stage of development, a variety of laboratory- and pilot-scale systems have been developed with promising potential (Lee et al 2011). One particular area of focus is taking advantage of the dark fermentation process in microorganisms.
Some systems have tried to find ideal conditions or mutate genes to [find and cite]. For example [cite]
Our project focuses on a modified strategy of producing hydrogen gas from Escherichia coli by simply knocking out and inserting select components to maximize hydrogen production through the dark fermentation process .
Strategy of Utilizing Fermentative Capabilities in E. Coli to Produce Hydrogen Gas:
Generally, the mixed acid fermentation of E. coli, which begins at the end of glycolysis, involves the production of lactate, acetate, formate, and ethanol from pyruvate [1].
Furthermore, pyruvate is also involved in the initial steps of dark fermentation, which is not naturally present in E. coli. Therefore, in order to preserve pyruvate for this process, the proteins responsible for producing lactate, acetyl-CoA, and formate were knocked out. The eliminated enzymes were lactate dehydrogenase A (ldhA) and pyruvate formate lyase B (pflB). Concurrently, pyruvate decarboxylase was inserted into the bacteria in order to produce acetaldehyde from pyruvate.
Originally, acetaldehyde in E. coli is converted into ethanol by alcohol dehydrogenase E (adhE) [2]. Thus, to preserve acetaldehyde for dark fermentation, adhE was also knocked out. Acetaldehyde dehydrogenase was then inserted into the E. coli to convert acetaldehyde into acetyl-CoA. The process of converting acetaldehyde into acetyl-CoA produces 2 NADH and 2 hydrogen protons. In addition, the glycolytic pathway also produces 2 NADH and 2 hydrogen protons. Thus, an expected total 4 NADH and 4 hydrogen protons are produced from one mole of glucose.
NADH is used to convert ferredoxin from its oxidized state into its reduced state. This reaction is carried out by ferredoxin oxidoreductase, which is inserted into the bacteria. Ferredoxin then reduces hydrogen protons into hydrogen gas with hydrogenase. As a result of the process, ferredoxin is returned to its oxidized state, enabling the cycle to continue.
We expect that eliminating ldhA, pflB, and adhE from the E. coli fermentation pathway and inserting mhpG, pyruvate decarboxylase, and ferredoxin oxidoreductase will ultimately yield 4 moles of hydrogen gas for every 1 mole of glucose consumed by the bacteria, thus achieving a more direct line towards hydrogen production.
References:
1. Cortassa S, Aon MA, Iglesias AA, Lloyd D. (2002) An Introduction to Metabolic and Cellular Engineering. Singapore: World Scientific, 1-34.
2. Gupta S et. al. (2000) Acetaldehyde dehydrogenase activity of the AdhE protein of Escherichia coli is inhibited by intermediates in ubiquinone synthesis. FEMS Microbiology Letters 182, 51-55
3. Forsberg, C.W., 2007. Future hydrogen markets for large-scale hydrogen production systems. Int. J. Hydrogen Energy 32, 431–439.
4. Lee, D et. al. (2011) Dark fermentation on hydrogen production: pure culture. Bioresource Technology 102, 8393-8402
Using NADH ferredoxin oxidoreductase as an electron carrier to shuttle electrons to the hydrogenase to lead to a production in hydrogen gas. Using transduction of the adhE knockout of JW1228-1 to FMJ39 will produce a triple knockout of IdhA, pflB, and adhE. Later, Insertions of mhpF, pyruvate decarboxylase and ferredoxin oxidoreductase will result in a theorhetical production of 4 mol Hydrogen gas per mol of glucose (when the bacteria is placed under fermentation conditions).
Protocols
Magazorb DNA Mini Prep Kit,Promega
Roche Agarose Gel for Electrophoresis
Restriction Enzyme Digest EcoRI
P1 Transduction - Ausubel, F. M. (2001). Current protocols in molecular biology. New York: J. Wiley
Plasmid Transformation [ie. CaCl2 transformation] - Ausubel, F. M. (2001). Current protocols in molecular biology. New York: J. Wiley
Future Work
In our current project, we used NADH ferredoxin oxidoreductase as an electron carrier to shuttle electrons to the hydrogenase and lead to hydrogen production. However, there are other pathways which may yield more hydrogen. In future experiments, we would like to do a qualitative analysis on our system and deduce its efficiency. The bacteria transformed for this project (the FMJ39 strain) may have some pathways which may breakdown hydrogen thus reducing yield. We would like to further study the genome of our microbe and minimize the use of such pathways to maximize our yield.
Our transformed bacteria rely on dark-fermentation to produce hydrogen. However, according to Nath, Kumar, and Das, photo-fermentation is a slightly more advantageous pathway because it is capable of harnessing light energy to drive the reactions in the cell (2005). It also has the advantage of breaking down small organic acids, such as acetyl-CoA in our model, and producing more hydrogen. An efficient system may result from the combination of our model and a photo-fermentation model. Our model is capable of using many compounds and shuttle them to hydrogen production but produces byproducts which cannot be broken down further. The photo-fermentation pathway is capable of using light energy to break down these smaller byproducts and produce more hydrogen.
Our current project took a commonly found fermentation process and modified it to create a funnel for hydrogen production. However, to build a complete and reliable system, we would like to add another system which is capable of producing the substrates needed for the current project. We have identified the breakdown of cellulose, common plant matter, as a potential candidate for this.
Combining a system for cellulose breakdown, dark-fermentation hydrogen production, and photo-fermentation hydrogen production will yield a complete system capable of using raw plant matter to produce hydrogen.
