MICROBIAL FUEL: Scientists have transformed E. coli to produce diesel and other hydrocarbons from sugars--as well as secrete enzymes to break down cellulose.
Image: © iStockphoto.com / Erik van Hannen
More In This Article
Listen to this Podcast
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
The bacteria responsible for most cases of food poisoning in the U.S. has been turned into an efficient biological factory to make chemicals, medicines and, now, fuels. Chemical engineer Jay Keasling of the University of California, Berkeley, and his colleagues have manipulated the genetic code of Escherichia coli, a common gut bacteria, so that it can chew up plant-derived sugar to produce diesel and other hydrocarbons, according to results published in the January 28 issue of Nature. (Scientific American is part of Nature Publishing Group.)
"We incorporated genes that enabled production of biodiesel—esters [organic compounds] of fatty acids and ethanol—directly," Keasling explains. "The fuel that is produced by our E. coli can be used directly as biodiesel. In contrast, fats or oils from plants must be chemically esterified before they can be used."
Perhaps more importantly, the researchers have also imported genes that allow E. coli to secrete enzymes that break down the tough material that makes up the bulk of plants—cellulose, specifically hemicellulose—and produce the sugar needed to fuel this process. "The organism can produce the fuel from a very inexpensive sugar supply, namely cellulosic biomass," Keasling adds.
The E. coli directly secretes the resulting biodiesel, which then floats to the top of a fermentation vat, so there is neither the necessity for distillation or other purification processes nor the need, as in biodiesel from algae, to break the cell to get the oil out.
This new process for transforming E. coli into a cellulosic biodiesel refinery involves the tools of synthetic biology. For example, Keasling and his team cloned genes from Clostridium stercorarium and Bacteroides ovatus—bacteria that thrive in soil and the guts of plant-eating animals, respectively—which produce enzymes that break down cellulose. The team then added an extra bit of genetic code in the form of short amino acid sequences that instruct the altered E. coli cells to secrete the bacterial enzyme, which breaks down the plant cellulose, turning it into sugar; the E. coli in turn transforms that sugar into biodiesel.
The process is perfect for making hydrocarbons with at least 12 carbon atoms in them, ranging from diesel to chemical precursors—and even jet fuel, or kerosene. But it cannot, yet, make shorter chain hydrocarbons like gasoline. "Gasoline tends to contain short-chain hydrocarbons, say C8, with more branches, whereas diesel and jet fuel contain long-chain hydrocarbons with few branches," Keasling notes. "There are other ways to make gasoline. We are working on these technologies, as well."
After all, the U.S. alone burns some 530 billion liters of gasoline a year, compared with just 7.5 billion liters of biodiesel. But Keasling has estimated in the past that a mere 40.5 million hectares of Miscanthus giganteus—a more than three-meter tall Asian grass—chewed up by specially engineered microbes, like the E. coli here, could produce enough fuel to meet all U.S. transportation needs.* That's roughly one quarter of the current amount of land devoted to raising crops in the U.S.
E. coli is the most likely candidate for such work, because it is an extremely well-studied organism as well as a hardy one. "E. coli tolerated the genetic changes quite well," Keasling says. "It was somewhat surprising. Because all organisms require fatty acids for their cell membrane to survive, if you rob them of some fatty acids, they turn up the fatty acid biosynthesis to make up for the depletion."
E. coli "grows fast, three times faster than yeast, 50 times faster than Mycoplasma, 100 times faster than most agricultural microbes," explains geneticist and technology developer George Church at Harvard Medical School, who was not involved in this research. "It can survive in detergents or gasoline that will kill lesser creatures, like us. It's fairly easily manipulated." Plus, E. coli can be turned into a microbial factory for almost anything that is presently manufactured but organic—from electrical conductors to fuel. "If it's organic, then, immediately, it becomes plausible that you can make it with biological systems."
The idea in this case is to produce a batch of biofuel from a single colony through E. coli's natural ability to proliferate and, after producing the fuel, dispose of the E. coli and start anew with a fresh colony, according to Keasling. "This minimizes the mutations that might arise if one continually subcultured the microbe," he says. The idea is also to engineer the new organism, deleting key metabolic pathways, such that it would never survive in the wild in order to prevent escapes with unintended environmental impacts, among other dangers.
But ranging outside of its natural processes, E. coli is not the most efficient producer of biofuel. "We are at about 10 percent of the theoretical maximum yield from sugar," Keasling notes. "We would like to be at 80 to 90 percent to make this commercially viable. Furthermore, we would need a large-scale production process," such as 100,000 liter tanks to allow mass production of microbial fuel.
Nevertheless, several companies, including LS9, which helped with the research, as well as Gevo and Keasling-founded Amyris Biotechnologies, are working on making fuel from microbes a reality at the pump—not just at the beer tap.
*Erratum (1/28/10): This sentence was edited after publication to correct a measurement conversion error in the number of hectares stated.
See what we're tweeting about
23 Comments
Add CommentLike all the rest of these early phase/concept solutions.... the proof is in the pudding... we'll see what happens in 5 more years...
Reply | Report Abuse | Link to thisPlease verify the number of hectares being used for agriculture in the US. I believe you are off by two orders of magnitude. This is a critical error, because it would make one falsely believe that we would loose one quarter of our food production by the replacement of petrofuels by biofuels.
Reply | Report Abuse | Link to thisI agree with rwk, the numbers for land cultivation are wildly out - they amount to the total agricultural land use in the US being a square 126km on each side - I think not. Come on guys get the simple maths right.
Reply | Report Abuse | Link to thisSomething is wrong with the numbers. 400,000 ha is 0.25% of the arable land in the U.S.A. And 140 billion gallons from 400,000 ha is 350,000 gallons/ha (141,000 gallons/acre).
Reply | Report Abuse | Link to thisThanks for catching that. Blame it on my early indoctrination in the imperial system. Figure is 100 million acres which was poorly converted to just 400,000 hectares. Actual figure should be 40 million hectares, which I'll now change.
Reply | Report Abuse | Link to thisBy the way, 442 million acres is the USDA estimate, just in case you're wondering where we got that one-quarter figure.
http://www.ers.usda.gov/publications/eib14/
Thanks.
Thanks for catching that. Blame it on my early indoctrination in the imperial system. Figure is 100 million acres which was poorly converted to just 400,000 hectares. Actual figure should be 40 million hectares, which I'll now change.
Reply | Report Abuse | Link to thisBy the way, 442 million acres is the USDA estimate, just in case you're wondering where we got that one-quarter figure.
http://www.ers.usda.gov/publications/eib14/
Thanks.
This is pretty cool you know...assuming that it will all go to plan and work in our favor.
Reply | Report Abuse | Link to thisI think this is pretty cool as long as everything goes according to plan. A real energy saver.
Reply | Report Abuse | Link to thisBut we are living in a world which is facing a food crisis and a population explosion, not to mention the probable loss of millions of hectares of agricultural land from rising sea levels.
Reply | Report Abuse | Link to thisDiverting land from food crops to making bio diesel however efficiently, doesn't seem credible to me.
Bertie Fox,
Reply | Report Abuse | Link to thisFirstly, the estimate of 1/4 of agricultural land being used for energy crops is on the high side. It's more likely to be considerably less, as more productive crops and methods of turning biomass into fuel are found. Biofuels won't be implemented alone: there will be many other energy-conserving methods used.
Besides that, there are many other ways to improve the availability of food. There is an amazing amount of waste and inefficiency in the world's food production. But changing eating habits would also free up large amounts of agricultural capacity, for instance if less meat were consumed. There is also the issue of the rising oceans, which would be curtailed if carbon were removed from the atmosphere by the use of energy crops like Miscanthus x Giganteus, which will store carbon in a large root system, while the above-ground crop will be carbon-neutral.
But yes, we need to contain the population explosion. But how to do this ethically, is problematic.
Bear in mind that they are talking about growing grasses. Grasses can be grown and harvested on land other than prime agricultural land, so it need not displace agricultural crops. Also, consider that the food crisis is much more about distribution than about production. Which not to say that any crop can be grown anywhere, but that biofuels need not impact the food supply.
Reply | Report Abuse | Link to thisЭсли эта технология применима для быстрой переработки целюлозы в отходах, то мы можем производить новое уникальное кластерное топливо. Оно содержит кислород и работает без выбросов в окружающую среду. Новое топливо возобновляется и сохраняет экологию.
Reply | Report Abuse | Link to thisPossibly is this technology applicable for the rapid processing of wastes? Then we can produce a new unique cluster fuel. It contains oxygen and works without extrass in an environment. A new fuel recommences and saves ecology.
Reply | Report Abuse | Link to thisI am interesed in becoming involved in developing and/or producing biofuels in upstate south Carolina. For info and
Reply | Report Abuse | Link to thisresume email: going_don@yahoo.com
If this bacteria escapes the lab, will it eat my house and turn it into diesel fule?
Reply | Report Abuse | Link to thisVeru interesting and very important. But, will this method, unlike others, be implemented?
Reply | Report Abuse | Link to thisDongoing : Eprida are making biomass pyrolysis retorts to produce biogas and/or biofuels. See www.eprida.com for technical and contact details.
Reply | Report Abuse | Link to thisIt is a pity no mention was made in the above article of the time taken to process a whole batch of algae. (Say 1000 litres).
What guarantee is there that some modified E.Coli will not get into the human gut and give us all very exotic diarrhea?
Reply | Report Abuse | Link to thisAll appears, as soon as a population will confide in - that at burning is the source of heat. We understood. It is a not carbon!
Reply | Report Abuse | Link to thisFor complete ecology it is needed to prepare a cluster fuel. It to do we are already able.
Все образуется, как только населению откроется - что при горении является источником тепла. Мы разобрались. Это не углерод!
Для полной экологии нужно готовить кластерное топливо. Это делать мы уже умеем.
Все образуется, как только населению откроется - что при горении является источником тепла. Мы разобрались. Это не углерод!
Reply | Report Abuse | Link to thisДля полной экологии нужно готовить кластерное топливо. Это делать мы уже умеем.
All appears, as soon as a population will confide in - that at burning is the source of heat. We understood. It is a not carbon!
For complete ecology it is needed to prepare a cluster fuel. It to do we are already able
ментарий здесь.
...
Reply | Report Abuse | Link to thisI have been working on forest biomass studies in Canada for a while. Only in forest management wastes, I heard that forest managed area USA could provide on a sustainable basis around 300 millions of dry tons of wasted biomass for energy purpose. Probably less in Canada due to access limitations.
Reply | Report Abuse | Link to thisTherefore, this could contribute for 25% of the total need, reducing requirements of agricultural land.
GuyG : Biomass Pyrolysis is far more eco-friendly than simply burning forest wastes for heat. Pyrolysis burns the hydrogen content, leaving the carbon as biochar which can be put back into the soil. The forest need not be clear-cut, but can be pollarded to encourage regrowth, preserving total biodiversity. And by sequestering carbon (from CO2 captured by the tree), the whole process is enhanced by carbon credits. See www.eprida.com for commercial and technical details.
Reply | Report Abuse | Link to this