BACKGROUNDThe discovery of deep eutectic solvents (DESs) has introduced a new class of promising green solvents to overcome many drawbacks associated with organic solvents. In this study, the synergistic effects of the components in the form of DESs on bacterial viability, membrane integrity, and retention of metabolic activity as well as the efficiency of 1,2-dehydrogeneration of cortisone acetate (CA) using whole cells of Arthrobacter simplex were investigated. RESULTSThe agar disc diffusion method, viability assays and the retention of sugar metabolic activity were used to investigate their toxicity to A. simplex. The results indicated that colinium salts were more toxic than the corresponding hydrogen bond donor (HBDs), but their deleterious effect could be weakened by incorporating them into DESs. Moreover, the best catalytic performance was found in the ChCl:U-(DES)-containing system when 1,2-dehydrogeneration using A. simplex was carried out in three different systems followed by the addition of DES, their components and their mixtures, respectively. In addition, metabolites with significantly changed concentration were identified by means of gas chromatography-mass spectrometry (GC-MS) and principal component analysis, which revealed five compounds that may be used as potential indicators to discriminate the effects of different concentrations of DESs on A. simplex. CONCLUSIONThe cholinium salts used in this study were toxic to A. simplex to some extent, while synergistic effects were observed after DES formation. The efficient biotransformation in DESs especially in the ChCl:U-(DES)-containing system potentially offers a promising strategy for the production of many different steroids. (c) 2018 Society of Chemical Industry