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BESC team engineers microbe for direct production of isobutanol from cellulose

Using consolidated bioprocessing, a team of researchers at the US Department of Energy’s BioEnergy Science Center (BESC), led by Dr. James Liao of UCLA, has for the first time produced isobutanol—an alcohol that is more attractive for transportation use than ethanol—directly from cellulose using a genetically engineered microbe. The team’s work, published online in the journal Applied and Environmental Microbiology, represents across-the-board savings in processing costs and time.

Last year, the US Environmental Protection Agency (EPA) selected Dr. Liao as the recipient of the 2010 Presidential Green Chemistry Challenge Academic Award for his work in genetically engineering microorganisms to make higher alcohols (those with more than two carbons in the molecule) from glucose or directly from carbon dioxide. (Earlier post.) Liao is also co-founder and board member of Easel Biotechnologies and a founder of Gevo.

Unlike ethanol, isobutanol can be blended at any ratio with gasoline and should eliminate the need for dedicated infrastructure in tanks or vehicles. Plus, it may be possible to use isobutanol directly in current engines without modification.

—James Liao

Higher alcohols such as isobutanol are better candidates for gasoline replacement because they have an energy density, octane value and Reid vapor pressure that is much closer to gasoline, Liao said.

While cellulosic biomass like corn stover and switchgrass is abundant and cheap, it is much more difficult to utilize than corn and sugar cane. This is due in large part because of recalcitrance, or a plant’s natural defenses to being chemically dismantled. Adding to the complexity and cost is the need for several steps—pretreatment, enzyme treatment and fermentation—resulting in a process that is more costly than a method that combines biomass utilization and the fermentation of sugars to biofuel into a single process.

To make the conversion possible, Liao and postdoctoral researcher Wendy Higashide of UCLA and Yongchao Li and Yunfeng Yang of Oak Ridge National Laboratory (ORNL) developed a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, that could synthesize isobutanol directly from cellulose. This work was on Liao’s earlier work at UCLA in building a synthetic pathway for isobutanol production.

Producing biofuels directly from cellulose, known as consolidated bioprocessing, is believed to reduce costs substantially compared to a process in which cellulose degradation and fermentation to fuel are accomplished in separate steps. Here we present a metabolic engineering example to develop a Clostridium cellulolyticum strain for isobutanol synthesis directly from cellulose. This strategy exploits the host’s natural cellulolytic activity and the amino acid biosynthetic pathway and diverts its 2-keto acid intermediates for alcohol synthesis. Specifically, we have demonstrated the first isobutanol production to approximately 660 mg/L from crystalline cellulose using this microorganism.

—Higashide et al.

While some Clostridium species produce butanol, these organisms typically do not digest cellulose directly. Other Clostridium species digest cellulose but do not produce butanol. None produce isobutanol, an isomer of butanol.

In nature, no microorganisms have been identified that possess all of the characteristics necessary for the ideal consolidated bioprocessing strain, so we knew we had to genetically engineer a strain for this purpose.

—Yongchao Li

While there were many possible microbial candidates, the research team ultimately chose Clostridium cellulolyticum, which was originally isolated from decayed grass. The researchers noted that their strategy exploits the host’s natural cellulolytic activity and the amino acid biosynthetic pathway and diverts its intermediates to produce higher alcohol than ethanol.

The researchers also noted that Clostridium cellulolyticum has been genetically engineered to improve ethanol production, and this has led to additional more detailed research. Clostridium cellulolyticum has a sequenced genome available via DOE’s Joint Genome Institute. This proof of concept research sets the stage for studies that will likely involve genetic manipulation of other consolidated bioprocessing microorganisms.

This work was supported in part by BESC at ORNL and by UCLA-DOE Institute for Genomics and Proteomics.

BESC is one of three DOE Bioenergy Research Centers established by the DOE’s Office of Science in 2007. The centers support multidisciplinary, multi-institutional research teams pursuing the fundamental scientific breakthroughs needed to make production of cellulosic biofuels, or biofuels from nonfood plant fiber, cost-effective on a national scale. The centers are led by ORNL, Lawrence Berkeley National Laboratory and the University of Wisconsin-Madison in partnership with Michigan State University.


  • Wendy Higashide, Yongchao Li, Yunfeng Yang, and James C. Liao (2011) Metabolic Engineering of Clostridium Cellulolyticum for Isobutanol Production from Cellulose. Appl. Environ. Microbiol. doi: 10.1128/AEM.02454-10



Genetically engineered microbes --- SCARY!?


No it is not scary, these microbes are so specialized at doing one single thing that they become very weak and fragile and cannot survive out of the reactor they have been designed for.

Henry Gibson

N-butanol is perhaps better, but there is not enough biomass for the fuel that is needed. Humans have been genetically engineering other life forms at least since the dog was domesticated, but retro-viruses are genetically engineering most of the creatures on the earth.

Cerametec is promoting an ion membrane that uses electricity to directly produce synthesis gas from steam and CO2, and this gas can be made into a variety of fuels. For less than the cost of a fuel cell, there are techniques for burning hydrocarbon fuels and capturing the CO2 in liquid form to be recycled. The US army is investigating capturing the H2O for use instead.

GE bought the developers of the ZEBRA battery to make their version of it called the DURATHON, and when it is put into mass production it will be good enough and cheap enough for the limited range that most people drive.

Wright of Wrightspeed has identified the market for plug in hybrids, the heavy low efficiency vehicles that people use for personal transportation.

The new versions of cheap lead batteries are adequate for most of the vehicle use, especially if a range extender is provided ..HG..

Coke Machine

Since these guys are scientists, it would be nice if they would use the correct nomenclature. Isobutanol can be interprested in several different ways. Iso is used to refer to a compound that has the same chemical formula as another but the structure is different...thus the atoms are arranged differently in space. Thus the compound we are discussing could be 2-butanol, 2-methyl 1-propanol, or 2-methyl 2-propanol. All have the same chemical formula. It would be nice to know which chemical we are discussing so some of us could see the pathway where they may come up with the compound, or possibly even see a better way to do it as most of the people here seem to be very educated, even though we may differ on ways and means to an end.


Recent lower temperature, lower cost, ZEBRA type batteries could find applications in heavy vehicles and hybrid locomotives, coupled with appropriate range extenders. Eventually, when made lighter and whenever their low temps point has been lowered by a few more degrees, those batteries could be introduced into small trucks that we like so much.

Keep it up HG.

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