BACKGROUNDIonic liquids (ILs) have become increasingly attractive as alternatives for organic solvents. In this study, the influences of ILs on the cellular growth rate, cellular activity, cortisone acetate (CA) conversion, CA solubility, and cell membrane permeability of Arthrobacter simplex CPCC 140451 (ASP) were examined. RESULTSResults showed that ILs with 3 carbon atoms in their side chains increased CA conversion, CA solubility, and cell membrane permeability of ASP and universally inhibited the cellular growth rate and activity, with ILs with [PF6]-anion exhibiting the most severe inhibition activity. Inhibition was also more serious using ILs with longer alkyl side chains and at higher concentrations. CA conversion, CA solubility, and leakage of cell inclusions showed higher increase under ILs with [PF6]-anion than those of ILs with [BF4]-anion and lower increase for ILs with longer side chains. CONCLUSIONThis study improved the understanding of the influence and primary selection of imidazolium-based ILs when applied in steroid biotransformation with Arthrobacter simplex whole cells. The data provided a foundation for the selection of suitable ILs for various applications. (c) 2017 Society of Chemical Industry