New Strategy Enhances Microbial Resistance to Inhibitory Pretreatment Chemicals

The Science

The chemical and physical processes for pretreating biomass help unravel the complex matrix of cell-wall components and enhance enzyme accessibility to these materials, but pretreatments also generate chemicals such as acetate that inhibit sugar fermentation to biofuels. Using a combination of adaptation, genetic engineering, and systems biology tools, BESC researchers have developed acetate-resistant strains of two industrial ethanol producers (the bacterium Zymomonas mobilis and the yeast Saccharomyces cerevisiae) by changing the expression of genes encoding transport proteins that move substances across the cell membrane. These proteins (called antiporters) transport proton and sodium ions and form gradients that are adversely impacted by the presence of acetate. By resequencing a Z. mobilis strain that had been adapted to withstand high acetate concentrations, BESC researchers discovered specific mutations in antiporter genes that enable acetate resistance. The specific antiporter mutations were validated using genetically engineered Z. mobilis and yeast showing the broad impact of these changes.

The Impact

Recent high oil prices, concerns over energy security, and environmental goals have reawakened interest in producing alternative fuels via large-scale industrial fermentation. Improvement in methods producing ethanol from cellulosic biomass is crucial in this goal. The development and deployment of robust ethanologenic microorganisms resistant to industrially relevant inhibitors and with high-yield ethanol production will be a critical component in the successful production of fuel ethanol in industrial-scale quantities.


Yang, S., M. L. Land, D. M. Klingeman, D. A. Pelletier, T.-Y. S. Lu, S. L. Martin, H.-B. Guo, J. C. Smith, and S. D. Brown. 2010. “Paradigm for Industrial Strain Improvement Identifies Sodium Acetate Tolerance Loci in Zymomonas mobilis and Saccharomyces cerevisiae,” Proceedings of the National Academy of Sciences 107(23), 10395–400. DOI:10.1073/pnas.0914506107.