Zach Baer
Graduate Student
University of California, Berkeley

B.S. Chemical and Biological Engineering, 2009
Rensselaer Polytechnic Institute

Office Location: 242 Energy Biosciences Building
Office Telephone: 510-666-2558

Improving Solvent Tolerance in Clostridia


The use of solventogenic clostridia to produce acetone, 1-butanol, and ethanol (ABE) has been conducted on an industrial scale since the 1920s. 1-Butanol has been identified as a potential biofuel component but already has a $5 billion worldwide market as a bulk chemical. Solventogenic clostridia are classified as gram positive, endospore-forming, anaerobic bacterium. Clostridia’s ability to ferment a variety mono- (xylose, glucose, arabinose, etc.) and disaccharides (cellobiose) makes it a very promising organism for lignocellulosic 1-butanol production. However, the acute toxicity of 1-butanol limits the overall solvent production to ~ 20 g/L. Two strategies that have been shown to increase 1-butanol titers in ABE fermentation are over-expression of heat shock proteins (GroES/EL) and extractive fermentation. Heat shock proteins or chaperones aid in protein folding/refolding and help to prevent protein aggregation in harsh environments (heat, high salinity, organic solvents, etc.). To date only native chaperones have been expressed in any species of solventogenic clostridia. The other strategy, extractive fermentation, utilizes a non-toxic, water-immiscible extractant, to selectively remove the 1-butanol in situ from the fermentation broth.

Project Goals:

1) To increase 1-butanol tolerance in clostridia without decreasing solvent titer, yield, or productivity. Specifically, by the expression of stress response proteins from a myriad of extremopholic organisms. This will require the development of a 1-butanol tolerance screen specific to solventogenic clostridia.

2) To increase 1-butanol and acetone titer by extractive fermentation, the ultimate goal being to condense these molecules into long-chain ketones for biodiesel applications.

3) To further increase chaperone activity in the presence of 1-butanol by directed evolution.