Ionic Liquids: Degrading Biomass but Not Biofuel-Producing Microbes
A major hurdle to the development of economically competitive biofuels remains the difficulty of separating long sugar chains from plant biomass (cellulose and hemicellulose) from the tough network of lignin that gives strength and resilience. Pretreatment of plant material by ionic liquids (ILs), a class of salts that are molten at room temperature, is highly effective in disrupting biomass structure and liberating cellulose chains for subsequent conversion to biofuel compounds by fermentative microbes. However, residual IL molecules are highly toxic to biofuel-producing microbes and must be fully removed from the cellulose fraction prior to conversion, an expensive and time-consuming process. To understand this IL toxicity and enable development of resistant strains of microbes, researchers at the Joint Bioenergy Institute (JBEI) examined shifts in gene expression of a novel biomass-degrading bacterium when exposed to an IL. Enterobacter lignolyticus was surprisingly resistant to IL exposure, altering its cell membrane composition, activating a series of pumps to remove IL from the cell interior, and balancing osmotic pressure across the cell membrane. Many of the response mechanisms were specific to IL exposure and were not triggered by exposure to standard salts. These findings provide new insights into the mechanisms used by microbes to tolerate exposure to ionic liquids and may lead to the improvement of IL tolerance in biofuel-producing microbes through targeted genetic engineering.
Khudyakov, J. I., P. D’haeseleer, S. E. Borglin, K. M. DeAngelis, H. Woo, E. A. Lindquist, T. C. Hazen, B. A. Simmons, and M. P. Thelen. 2012. “Global Transcriptome Response to Ionic Liquid by a Tropical Rain Forest Soil Bacterium, Enterobacter lignolyticus,” Proceedings of the National Academy of Sciences of the USA 109(32), E2173-E2182. DOI: 10.1073/pnas.1112750109.