Engineered E. Coli strain boosts biohydrogen production from sugar 140 times compared with wild type

Scientists at the Texas A&M University's chemical engineering department have genetically engineered the Escherichia Coli bacterium and boosted its capacity to produce biohydrogen from sugar. Professor Thomas Woods, of the Artie McFerrin Department of Chemical Engineering, modified a strain which produces up to 140 times more hydrogen than is created in a naturally occurring process. His findings about the potential of this gaseous biofuel are presented in an open access article in Microbial Biotechnology. The professor sees a future based on local and decentralised biohydrogen production, with the sugar feedstock being transported to mini-factories where the bacteria ferment it into the pure energy-rich gas.

Wood acknowledges that there is still much work to be done before his research translates into any kind of commercial application, but his initial success could prove to be a significant stepping stone on the path to the hydrogen-based economy that many believe could contribute greatly to cleaner mobility, the uptake of renewable, bio-based energy and strengthen energy security.

Renewable, clean and efficient hydrogen is the key ingredient in fuel-cell technology, which has the potential to power everything from portable electronics to automobiles and even entire power plants. Today, most of the hydrogen produced globally is created by a process known as electrolysis through which hydrogen is separated from the oxygen. But the process is expensive and requires vast amounts of primary energy - one of the chief reasons why the technology has yet to catch on. Alternatively, hydrogen can be produced by reforming fossil fuels (oil, coal, natural gas), but in that case the fuel isn't renewable nor clean and would lead to large amounts of greenhouse gas emissions during its production. The cleanest and most efficient way to produce hydrogen is from biomass - either via gasification or fermentation (previous post).

Wood's work with E. coli and biohydrogen is on track to solve the current problems surrounding hydrogen production. It takes the fermentation pathway (schematic, click to enlarge). By selectively deleting six specific genes in E. coli's DNA, the scientist and his collegues have basically transformed the bacterium into a mini biohydrogen-producing factory that's powered by sugar. Scientifically speaking, Wood has enhanced the bacteria's naturally occurring glucose-conversion process on a massive scale.

These bacteria have 5,000 genes that enable them to survive environmental changes. When we knock things out, the bacteria become less competitive. We haven't given them an ability to do something. They don't gain anything here; they lose. The bacteria that we're making are less competitive and less harmful because of what's been removed. - Professor Thomas Woods

With sugar as its main power source, this strain of E. coli can now take advantage of existing and ever-expanding scientific processes aimed at producing sugar from energy crops.

A lot of people are working on converting something that you grow into some kind of sugar. We want to take that sugar and make it into hydrogen. We're going to get sugar from some crop somewhere. We're going to get some form of sugar-like molecule and use the bacteria to convert that into hydrogen. - Professor Woods

Biological methods such as this - E. coli producing hydrogen through a fermentative process - are likely to reduce energy costs since these processes don't require extensive heating or electricity. They are an alternative to thermochemical and electrolysis-based hydrogen production:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: bacteria :: sugar :: fermentation :: efficiency :: biohydrogen ::

One of the most difficult things about chemical engineering is how you get the product, Wood explained. In this case, it's very easy because the hydrogen is a gas, and it just bubbles out of the solution. You just catch the gas as it comes out of the glass. That's it. You have pure hydrogen.

Decentralised production
There also are other benefits. As might be expected, the cost of building an entirely new pipeline to transport hydrogen is a significant deterrent in the utilization of hydrogen-based fuel cell technology. In addition, there is also increased risk when transporting hydrogen. The solution, Wood believes, is converting hydrogen on site.

The main thing we think is you can transport things like sugar, and if you spill the sugar there is not a huge catastrophe, Wood said. The idea is to make the hydrogen where you need it.

Of course, all of this is down the road. Right now, Wood remains busy in the lab, working on refining a process that's already hinted at its incredible potential. The goal, he said, is to continue to get more out of less.

Take your house, for example. The size of the reactor that we'd need today if we implemented this technology would be less than the size of a 250-gallon fuel tank found in the typical east-coast home. I'm not finished with this yet, but at this point if we implemented the technology right now, you or a machine would have to shovel in about the weight of a man every day so that the reactor could provide enough hydrogen to take care of the average American home for a 24-hour period. - Professor Woods

The scientists are now trying to make bacteria that don't require 80 kilograms but closer to 8 kilograms.

Schematic: sketch of fermentative hydrogen production in Escherichia coli. Hydrogen is produced from formate by the formate hydrogen lyase (FHL) system [hydrogenase 3 and formate dehydrogenase-H (FDHH)], which is activated by FhlA (that is regulated by Fnr) and repressed by HycA. Evolved hydrogen is consumed through the hydrogen uptake activity of hydrogenase 1 and hydrogenase 2. Formate is exported by FocA and/or FocB and is metabolized by formate dehydrogenase-N (FDHN) which is linked with nitrate reductase A and formate dehydrogenase-O (FDHO). Cyanobacterial hydrogenases (HoxEFUYH) derived from Synechocystis sp. PCC 6803 inhibit the activity of E. coli hydrogenase 1 and hydrogenase 2 resulting in enhanced hydrogen yield.

References:
Toshinari Maeda, Viviana Sanchez-Torres, Thomas K. Wood, "Metabolic engineering to enhance bacterial hydrogen production" [open access], Microbial Biotechnology 1 (1), 2008, 30–39, doi:10.1111/j.1751-7915.2007.00003.x

Texas A & M University: Wood envisions "E. Coli" as future source of energy - January 29, 2008.

Biopact: Biohydrogen, a way to revive the 'hydrogen economy'? - August 20, 2006