BACKGROUNDAs a low-cost alternative to the traditional ionic liquids (ILs), deep eutectic solvents (DESs) have currently attracted increasing attention for their various applications including biocatalysis. This study aimed at analyzing the effect of DESs on 1, 2-dehydrogeneration of cortisone acetate(CA) to prednisone acetate (PA) by Arthrobacter simplex. RESULTSOf the three DESs examined, ChCl:U was successfully employed as co-solvent to improve the bioconversion efficiency. For substrate feeding concentration of 5gL(-1), substrate conversion reached 93% by immobilized A. simplex cells (4 g(DW) L-1) with ChCl:U content of 6%, which is more efficient than conversions without DESs. Importantly, it has been shown that DESs and the immobilized cells can be easily recovered and then reused for five batches of bioconversion with a final conversion above 80%. CONCLUSIONOur results show the potential use of DESs-based systems in industrial steroid biodehydrogenation by A. simplex, and provide an environmentally benign means of steroid biotransformation. (c) 2015 Society of Chemical Industry