Isobutanol From Cellulose Hailed as Biofuel Promise

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A team at the BioEnergy Science Center (BESC) announced that it succeeded to produce isobutanol directly from cellulose. It is the first time anyone does that.

The process presents several advantages, including saving time and money. Besides, isobutanol is a higher-grade of alcohol than ethanol.

“Unlike ethanol, isobutanol can be blended at any ratio with gasoline and should eliminate the need for dedicated infrastructure in tanks or vehicles,” said James Liao, chancellor’s professor and vice chair of Chemical and Biomolecular Engineering at the UCLA Henry Samueli School of Engineering and Applied Science.

“Plus, it may be possible to use isobutanol directly in current engines without modification. Compared to ethanol, higher alcohols such as isobutanol are better candidates for gasoline replacement because they have an energy density, octane value and Reid vapor pressure – a measurement of volatility – that is much closer to gasoline”, Liao added.

Process

One of the problems with corn stover and switchgrass in terms of conversion of cellulosic biomass to alcohol is that they are more recalcitrant, that is, they are harder to dismantle chemically. Besides, several steps are involved in the process (pretreatment, enzyme treatment and fermentation), involving higher costs. Combining biomass utilization and the fermentation of sugars to biofuel into a single process is more financially attractive.

To make the conversion possible, Liao and his team developed a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe that could synthesize isobutanol directly from cellulose.

“This work is based on our earlier work at UCLA in building a synthetic pathway for isobutanol production,” Liao said.

Some bio-tweaking was necessary, though. 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,” researcher Yongchao Li said.

The choice fell on Clostridium cellulolyticum, which was originally isolated from decayed grass. The method exploits the host’s natural cellulolytic activity and the amino acid biosynthetic pathway and diverts its intermediates to produce higher alcohol than ethanol.

In response to the announcement, U.S. Energy Secretary Steven Chu said it is another sign of the rapid progress in the development of biofuels that can help reduce oil dependence.

The paper “Metabolic Engineering of Clostridium Cellulolyticum for Isobutanol Production from Cellulose” is available online. The research was supported in part by BESC at ORNL and UCLA-DOE Institute for Genomics and Proteomics.

Article by Antonio Pasolini, appearing courtesy Justmeans.

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