Ionic liquid tolerance in microbes

A major aim of industrial biotechnology is to unlock the nearly limitless supply of sugar in plant cell walls in order to support microbial growth for commodity chemical and biofuel production.  Ionic liquid (IL) solvents are among the best tools for gaining access to the sugars in otherwise recalcitrant biomass.  However, IL-treated-biomass sugars are inevitably plagued by residual ILs that inhibit growth in industrial bacteria and yeast, thereby preventing chemical production by these organisms.  IL toxicity is, therefore, a critical roadblock in many industrial pathways, including the Joint BioEnergy Institute’s biofuels pipeline.  Focusing on a common imidazolium–based IL, our group has made substantial headway into this problem.  Here, we describe our identification of several membrane transporters that export IL from E. coli as well as our investigation of a natural S. cerevisiae isolate of exceptional IL tolerance.  We describe our metagenomic screening strategy for identifying genes that permit laboratory strains of both organisms to grow in unprecedented levels of ionic liquids.  In ongoing studies, we are probing IL tolerance from both a scientific and engineering perspective, investigating (1) the native functions of these genes and (2) how we can use them to maximally engineer IL tolerance into industrial strains and fully overcome this key gap in biofuels and industrial chemical production processes.