S158: Ionic liquid tolerance in Enterobacter cloaceae, a lignocellulolytic bacterium isolated from tropical rain forest soil

Lignocellulosic biofuels hold great promise for alleviating the nation’s energy needs and dependence on foreign oil. Biomass is highly recalcitrant to degradation, which can be overcome by pretreatment with ionic liquids, greatly increasing its solubility (Singh et al., 2009). Pretreated plant material is further degraded into sugar monomers by enzymes derived from lignocellulolytic microorganisms, and subsequently fermented to produce ethanol. However, ionic liquids carried over from the pretreatment step are toxic to the organisms used subsequently.  Enterobacter cloaceae strain SCF1 is a gram-negative bacterium with high biomass degradation activity which was isolated from a Puerto Rico tropical rain forest soil community. We find that SCF1 can grow in the presence of ionic liquids such as 1-ethyl-3-methylimidazolium ([EMIM]) chloride and [EMIM] acetate. Tolerance to ionic liquid can be increased by the addition of sodium chloride or sodium acetate, possibly by providing cross-protection from the salt stress response or due to osmotic regulation using extracellular ions. Growth in ionic liquid causes an increase in bulky phospholipid fatty acids, suggesting that rigidification of the SCF1 cell membrane may constitute an effective tolerance mechanism. We are using transcriptomics to analyze gene expression changes that underlie these and other ionic liquid tolerance mechanisms, with the goal of identifying novel genes which may be used to engineer solvent tolerant microorganisms for the industrial biofuels process.