Oak Ridge National Laboratory has announced two of its scientists, Yongchao Li and Yunfeng Yang of ORNL collaborating with a team led by James Liao of the University of California at Los Angeles has for the first time produced isobutanol directly from cellulose.  This achievement has been for years a prime national goal, as it would answer a major effort to move more transport fuel demand away from imported oil.

Butanol is a four-carbon atom rather than the two-carbon atom of ethanol.  Its properties include energy density much closer to gasoline, a high octane more like ethanol, and it doesn’t mix with water as ethanol will.

Liao, chancellor’s professor and vice chair of Chemical and Biomolecular Engineering at the UCLA Henry Samueli School of Engineering and Applied Science explains why butanol is so desirable, “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.”

The team’s work represents across-the-board savings in processing costs and time, plus isobutanol is a more energy dense alcohol buy about a third than ethanol.  The team’s paper has been published online in Applied and Environmental Microbiology.

Cellulosic biomass like wood products, the grasses and crop residues are abundant and could be cheap, but are much more difficult to utilize than starch ready corn and sugarcane. This is because of “recalcitrance” a property of plants natural defenses to being chemically dismantled.

Direct use of the biomass could solve the processing complexity and expense that involves several steps – pretreatment, enzyme treatment and fermentation – which is more costly than a method that combines biomass utilization and the fermentation of sugars to biofuel in a direct single process.

To accomplish the conversion the team designed and developed a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe that could directly synthesize isobutanol from cellulose.  Liao points out, “This work is based on our earlier work at UCLA in building a synthetic pathway for isobutanol production.”

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.

Now Li explains, “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.”

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

The researchers also note that Clostridium cellulolyticum has been genetically engineered to improve ethanol production, and this has led to additional detailed research.

Clostridium cellulolyticum has a sequenced genome available via U.S. Department of Energy’s’ Joint Genome Institute. The team’s proof of concept research sets the stage for studies that will likely involve genetic manipulation of other consolidated bioprocessing microorganisms.

This is encouraging research.  But butanol production to date shows two major issues the press release isn’t addressing.  The first is butanol is more toxic than ethanol, as butanol is produced and the proportion in the biomass mash increases, the organisms usually shut down or die.  How that is being addressed isn’t discussed.

The second issue is the utilization share of the available biomass.  Fermentation of corn and sugarcane as an example, nearly completely extracts the starches and sugars leaving the cellulose, proteins and oils in a highly useful state that earns income, offsets the cost of the crop and leaves almost no waste.

The UCLA ORNL team’s work deserves congratulations.  It not reasonable to expect they’re at the point where all that’s left is a mineral ash residue with all the carbon reformed into fuel. But it certainly looks much more simple now to get at least part of the cellulose biomass made into a drop in gasoline replacement fuel.


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