E. coli metabolism reversed for speedy production of fuels, chemicals

Aug 10, 2011
Rice University engineering researchers Ramon Gonzalez (left) and Clementina Dellomonaco reversed one of the most efficient of all metabolic pathways -- the beta oxidation cycle -- to engineer bacteria that make biofuels at a breakneck pace. Credit: Jeff Fitlow/Rice University

In a biotechnological tour de force, Rice University engineering researchers this week unveiled a new method for rapidly converting simple glucose into biofuels and petrochemical substitutes. In a paper published online in Nature, Rice's team described how it reversed one of the most efficient of all metabolic pathways -- the beta oxidation cycle -- to engineer bacteria that produce biofuel at a breakneck pace.

Just how fast are Rice's single-celled ? On a cell-per-cell basis, the bacteria produced the , a that can be substituted for gasoline in most engines, about 10 times faster than any previously reported organism.

"That's really not even a fair comparison because the other organisms used an expensive, enriched feedstock, and we used the cheapest thing you can imagine, just glucose and mineral salts," said Ramon Gonzalez, associate professor of chemical and biomolecular engineering at Rice and lead co-author of the Nature study.

Gonzalez's laboratory is in a race with hundreds of labs around the world to find green methods for producing chemicals like butanol that have historically come from petroleum.

"We call these 'drop-in' fuels and chemicals, because their structure and properties are very similar, sometimes identical, to petroleum-based products," he said. "That means they can be 'dropped in,' or substituted, for products that are produced today by the ."

Butanol is a relatively short molecule, with a backbone of just four carbon atoms. Molecules with longer carbon chains have been even more troublesome for biotech producers to make, particularly molecules with chains of 10 or more carbon atoms. Gonzalez said that's partly because researchers have focused on ramping up the natural metabolic processes that cells use to build long-chain fatty acids. Gonzalez and students Clementina Dellomonaco, James Clomburg and Elliot Miller took a completely different approach.

"Rather than going with the process nature uses to build fatty acids, we reversed the process that it uses to break them apart," Gonzalez said. "It's definitely unconventional, but it makes sense because the routes nature has selected to build fatty acids are very inefficient compared with the reversal of the route it uses to break them apart."

The beta oxidation process is one of biology's most fundamental, Gonzalez said. Species ranging from single-celled bacteria to human beings use beta oxidation to break down fatty acids and generate energy.

In the Nature study, Gonzalez's team reversed the beta oxidation cycle by selectively manipulating about a dozen genes in the bacteria Escherichia coli. They also showed that selective manipulations of particular genes could be used to produce of particular lengths, including long-chain molecules like stearic acid and palmitic acid, which have chains of more than a dozen .

"This is not a one-trick pony," Gonzalez said. "We can make many kinds of specialized molecules for many different markets. We can also do this in any organism. Some producers prefer to use industrial organisms other than E. coli, like algae or yeast. That's another advantage of using reverse-beta oxidation, because the pathway is present in almost every organism."

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User comments : 13

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Canman
1 / 5 (1) Aug 10, 2011
Ok, so where is the glucose going to come from ? Corn? Inefficient, not carbon neutral. Sugar cane? Maybe if you live in Brazil. Replaces one problem for another. Now the problem is, how do we produce huge quantities of glucose?
Adrenaline
not rated yet Aug 10, 2011
Sweet sorghum?
antonima
5 / 5 (1) Aug 10, 2011
Ok, so where is the glucose going to come from ? Corn? Inefficient, not carbon neutral. Sugar cane? Maybe if you live in Brazil. Replaces one problem for another. Now the problem is, how do we produce huge quantities of glucose?


Glucose is extremely abundant - it is the sole building block of the polymer cellulose, the stuff that basically all plants are made of.
Myno
5 / 5 (1) Aug 10, 2011
Ok, so how difficult is it to break cellulose down into glucose? I thought cellulose was pretty dang stable stuff.
antonima
not rated yet Aug 10, 2011
It is the more difficult part of the process, or at least the part that we have to still figure out. There are many many approaches to doing it, including steam treatment but also microbe treatment. It is still fairly inefficient, but if I remember right there are even a few profitable operations in China as of today.
Sanescience
not rated yet Aug 10, 2011
The feedstock will have it's own modifications.

Switch grass modified for easy digestion.

http://arstechnic...uels.ars
irjsiq
not rated yet Aug 11, 2011
"... reversed one of the most efficient of all metabolic pathways -- the beta oxidation cycle ...
combined with the probability that many other Bacteria operate with similarly, very rapid 'digestion of Cellulose' should soon be available.
Due to the logistical expense of transporting 'Broom Grass' to refineries, just make small 'Digesting Refineries' for use right in the fields ... gather into Threshing Machines, and dump directly into the on-site refinery. The Fuel could power the farm equipment, irrigation systems, 'Generators' to Power the Farm Operations!
_nigmatic10
not rated yet Aug 11, 2011
Woot! Poop fuel!
wwqq
1 / 5 (1) Aug 11, 2011
Cellulosic fuels are as much of a non-starter now as they ever were. There's simply litle or no free cellulose available. It's problematic to keep soil carbon with existing crops, especially with corn; crop wastes aren't waste and there's not much there you can take.

Food production will need to increase by about a factor of 2 this century. Much of that can come from crop yields, but a significant chunk will likely have to come from marshalling more of net primary production for human uses.

Marginal lands aren't very productive. You're going to conscript vast resources from natural uses and it's still going to be a nightmare trying to collect and use this sparse resource of questionable economic value.
Birger
not rated yet Aug 11, 2011
A GM crop could be provided with a "trigger" that will start it churning out cellulase (cellulose-breaking enzymes) if exposed to the right chemical trigger just before harvesting.

BTW, isn't butanol better than ethanol in that it does not allow water to dissolve in it? Ethanol has a tendency to make stuff rust because of the water content.

To make it easier to use marginal lands I suggest including the genes for making bacteria-carrying nodules in the root system, enabling the crops to fixate nitrogen.
wwqq
1 / 5 (1) Aug 12, 2011
A GM crop could be provided with a "trigger" that will start it churning out cellulase[...]


That's plausible but potentially dangerous. It's also plausible for bacteria to stumble onto that trigger and eat your crops. If you depend on those crops to produce significant quantities of fuel(or worse, food AND fuel) you're in trouble.

If those crops grow food and fuel you have to leave most of the cellulose in the field anyway, because otherwise you're just mining soil carbon; stealing from the future and calling it GDP.

BTW, isn't butanol better than ethanol in that it does not allow water to dissolve in it?


Butanol is not very soluble in water; when the concentration goes high enough it naturally separates out and floats to the surface. It is a very good diesel replacement.

To make it easier to use marginal lands[...]


Marginal land is by definition of marginal economic utility; it doesn't have to be marginal in terms of biodiversity or natural beauty.
PinkElephant
5 / 5 (1) Aug 12, 2011
otherwise you're just mining soil carbon; stealing from the future and calling it GDP
Most of the carbon in any plant comes from the atmosphere (by ingestion of CO2) rather than from soil. In fact, cultivating perennial crops such as switchgrass that develop extensive root systems, you wind up over time adding more carbon to the soil than there ever was before. And as a bonus, these "weeds" can grow pretty much anywhere -- including on otherwise very "marginal" lands.
wwqq
1 / 5 (1) Aug 16, 2011
PinkElephant, plants don't extract any carbon from the soil and I've never claimed that they do. Soil carbon is very important for soil fertility and soil stability. The reason you need to leave a lot of "crop waste" in the field is that soil carbon is always being lost to oxidation and being washed away.

In fact, cultivating perennial crops such as switchgrass that develop extensive root systems, you wind up over time adding more carbon to the soil than there ever was before.


You can, but that's not "free crop waste". You're either replacing food with fuel or appropriating more of NPP.

And as a bonus, these "weeds" can grow pretty much anywhere -- including on otherwise very "marginal" lands.


If you do your yields will be shit and the economics of gathering this resource questionable(see the collapse of jatropha).

Marginal land is defined as not very economical to farm. Marginal land can still be beautiful, biodiverse or provide important ecosystem services.