With the engineering of a microbe that improves isobutanol yields by a factor of 10 another barrier to commercially viable biofuels has fallen, according to a recent study published in the journal Metabolic Engineering.
The study has been conducted by scientists from the Department of Energy's BioEnergy Science Center (BESC). The new research builds on previous results from 2011 that reported on the first genetically engineered microbe able to directly produce isobutanol from cellulose.
Because of its energy density and octane values isobutanol makes an attractive alternative energy source. Those values are close to gasoline. This means that isobutanol is useful as a direct replacement for gasoline, but another advantage is that the product can also be used as a chemical feedstock for various derivate sub-products. For instance, isobutanol can be upgraded chemically to be used as a hydrocarbon equivalent for jet fuel.
The earlier study by BESC scientists at the University of California and DOE's Oak Ridge National Laboratory has proved in principle the potential applications of bioengineering in designing microbes to be used in isobutanol production.
This new research represents a significant step forward, according to co-author James Liao of UCLA's Henry Samueli School of Engineering and Applied Science. The initial findings of the study conducted four years ago were based on studying Clostridium celluloyticium. This is a less complex organism, according to the scientist. The new research was successful in engineering similar traits in a more complex microbe from a metabolic engineering perspective. Clostridium thermocellum allows much higher yielding and has taken the research to "new levels of consolidated bioprocessing efficiency", according to Liao.
Consolidated bioprocessing consists in bundling of several processes in a single microbe. The microorganism can extract sugar from a plant's cellulose and then convert it into a biofuel. This process combines several steps to produce biofuel at a lower cost. The new approach also helps to overcome the challenges of a plant's natural defenses to being chemically dismantled, called recalcitrance. Up to date, this was one of the main economic barriers to using lignocellulosic biomass such as switchgrass or corn stover as feedstock for biofuels.
Clostridium thermocellum has produced conversion results of 5 to 6 grams per liter compared to the previously genetically engineered microbe that could achieve only 0.6 gram of isobutanol per liter. This performance was accomplished by inserting five genes into the microbe in order to enable isobutanol synthesis. According to the scientists who took part in the research, this is a clear next-generation advance over previous strategies that used yeast to create biofuels from cellulose.