Tolerance Characterization and Isoprenol Production of Adapted Escherichia coli in the Presence of Ionic Liquids

Ionic liquid (IL)-based pretreatment makes lignocellulosic biomass more accessible to enzymes and improves enzymatic digestibility. However, the ILs left in biomass slurry after pretreatment could inhibit activity of enzymes and microbial fermentation. Therefore, it is necessary to develop robust host strains that are IL-tolerant. In this study, we characterized IL tolerance and biofuel production of adapted Escherichia coli obtained by adaptive laboratory evolution (ALE). We found that IL-tolerant E. coli obtained via ALE by 1-butyl-3-methylimidazolium chloride ([C 4 C 1 Im]Cl) showed improved growth in the presence of four ILs, [C 4 C 1 Im]Cl, 1-ethyl-3-methylimidazolium chloride ([C 2 C 1 Im]Cl), 1-butyl-3-methylimidazolium acetate ([C 4 C 1 Im][OAc]), and 1-ethyl-3-methylimidazolium acetate ([C 2 C 1 Im][OAc]) compared to that of the parent strain. The growth of adapted strain E. coli MG1655-A1 was even promoted by [C 4 C 1 Im]Cl and [C 2 C 1 Im]Cl of certain concentrations. The adapted strains were further transformed by introducing mevalonate-based metabolic pathway and they showed significantly increased isoprenol titer compared to parent strain E. coli MG1655. Furthermore, they were shown to use [C 4 C 1 Im][OAc] and [C 2 C 1 Im][OAc] as carbon sources and assimilate the acetate ions. These results indicated that ALE provided promising host strains for one-pot biofuel production