One-Stop “Shopping” for Biofuels: A Breakthrough in Consolidated Bioprocessing

The Science

In most current biomass-to-biofuel strategies, plant material must be first broken down into its component sugars and then converted to ethanol in a separate step, resulting in a costly and inefficient process. Researchers at the DOE Bioenergy Science Center (BESC) and the University of California–Los Angeles have now successfully engineered the cellulose-degrading bacterium Clostridium cellulolyticum to convert cellulose directly to isobutanol, a liquid fuel with much higher energy density than ethanol and, unlike ethanol, with the potential to be directly used in current engines. This consolidated bioprocessing (CBP) approach, in which a single organism both deconstructs plant cellulose and converts it to a biofuel in one step, significantly improves overall process efficiency. Until now no single microbe was known to possess the necessary combination of biomass degradation and fuel synthesis properties, and the most promising organisms are extremely challenging to genetically manipulate. This breakthrough thus provides a promising new avenue to engineer similar organisms for single-step conversion of plant biomass to fuels.

Summary

Researchers present a metabolic engineering example for the development of a Clostridium cellulolyticum strain for isobutanol synthesis directly from cellulose. This strategy exploits the host’s natural cellulolytic activity and the amino acid biosynthesis pathway and diverts its 2-keto acid intermediates toward alcohol synthesis. Specifically, researchers demonstrated the first production of isobutanol to approximately 660 mg/liter from crystalline cellulose by using this microorganism.

Principal Investigator

James C. Liao
University of California–Los Angeles

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]

References

Higashide, W., Y. Li, Y. Yang, and J. C. Liao. 2011. “Metabolic Engineering of Clostridium cellulolyticumfor Isobutanol Production from Cellulose,” Applied and Environmental Microbiology. DOI:10.1128/AEM.02454-10.