Bacteria are notorious for making us sick and spoiling our food, yet it seems the bacterium E. coli might soon become a useful ally in conquering CO2 emissions from cars.
Tinkering with the DNA of various bacteria, James C. Liao, a professor from the Department of Chemical and Biomolecular Engineering at UCLA, has produced a biofuel from a strain of E. coli as an alternative to ethanol gasoline.
Despite the favorable coverage ethanol has received, it actually has several liabilities. Only a certain type of car is able to guzzle down the 85 percent ethanol gasoline and digest it without problems, and Liao's discovery would allow the insides of all cars to stay the same. Ethanol also absorbs water from the air and corrodes metal. The production of ethanol also requires 750 megatons of biomass, meaning it has a significant agricultural cost as well. These factors wipe out ethanol's economic advantage.
Fermenting foods has been a common pursuit throughout human history, whether turning barley into beer or culturing cheese. Bacteria can perform these transformations by using enzymes, small proteins that lower the amount of energy needed for a reaction, thus hastening the fermentation process. These enzymes also enable the bacteria to transform biomass into biofuel.
I am sure people would agree that to produce alcohols in this way is easy, but to produce it very efficiently, it is a big challenge,"" Liao said.
To produce the biofuel efficiently, Liao changed E. coli's enzymes so they would make an alcohol that produces more energy and will not corrode metal. This different type of biofuel is an alcohol with longer carbon chains, contrasting with ethanol's two-carbon chain, the source of its undesirable properties.
""The four- and five-carbon chains have a high energy content that is almost as high as gasoline,"" Liao said. ""[The new alcohol] also has no vehicle retrofitting and low production yield.""
Theoretically, this type of biofuel sounded very promising, but Liao needed to find a bacterium that could efficiently produce those long-carbon chain alcohols.
""In order for this to be a [competitive] biofuel, it needs to be efficient,"" Liao said. He needed a bacterium that can grow fast and is easy to manipulate, such as the infamous E. coli.
E. coli does not naturally have the right enzymes to transform biomass into a long-chained alcohol. Liao looked through science journals for previous research on bacterial pathways, and he eventually found different bacteria with genetic instructions for special enzymes that can make these long-carbon chains. After finding these genetic instructions, Liao said he inserted these genes directly into E. coli. The E. coli could then read the newly inserted instructions and make the special enzymes, which in turn produce the sought-after long-chained alcohols.
To test this approach with E. coli, Liao and his team tried to make isopropanol, a simple three-carbon chain alcohol. Just as Liao had hoped, E. coli produced the targeted isopropanol.
""This is the first time we could produce isopropanol from E. coli, which isn't produced by E. coli in the environment,"" Liao said. ""If you have the right enzymes and strategy, you can convert E. coli to produce the compound you are interested in.""
However, the E. coli wasn't producing the isopropanol very efficiently.
Liao and his team then tried ""knocking out competing pathways, in order to boost the concentration."" The multiple pathways are like multi-tasking in a bacterium or cell: each can make many different by-products that can be used for other functions. By eliminating these multitasking steps, the E. coli will only go through one step and focus all its energy to make one by-product, isopropanol.
""[This change in the pathways] produced more than the first project, but it still gave a low yield,"" Liao said. ""So at that point, we did some thinking. Why did this pathway work so poorly in E. coli.? So we went back to the drawing board.""
Liao wondered if he could use any other bacterial genes on the E. coli.
Again, Liao searched through science journals and found two other bacteria that made alcohols naturally. He cloned the enzymes they used and inserted them into E. coli. This time the E. coli produced isobutanol instead, and much more efficiently, with an 86 percent yield. (A yield of 100 percent would mean the bacteria produced all the possible isobutanol it could.)
To see if these types of alcohols would have a potential use in the market, Liao used a Chevy 350 V8 engine to test different mixtures of isobutanol with gasoline. He found that a gasoline mixture consisting of 20 percent isobutanol increased the miles per gallon by five percent.
Liao and his research team aren't stopping there, though. They hope to apply this method to other organisms to turn ordinary matter like cellulose - a plant sugar - and even CO2 into fuel.
""All you had to do is find the right enzyme,"" Liao said. ""If you are able to find the right chemistry and strategy, you can have a great impact.
