The effect of ethanol on cell properties and steroid 1-en-dehydrogenation biotransformation of Arthrobacter simplex

Resting cells of Arthrobacter simplex with 1-en-dehydrogenation ability were prepared and treated by ethanol at subinhibitory concentrations (4%-15%, v/v), then added into the ethanol-free system containing low concentration of cortisone acetate (1 g L(-1)) to produce prednisone acetate by C1,2 dehydrogenation reaction. Results showed that, within the range of ethanol concentration, the initial conversion rate was varied significantly with the concentration of ethanol and the maximum was obtained at 8% (v/v) ethanol, which was increased by 32.6% compared with the control. A series of cell features closely relevant to biotransformation efficiency were further analyzed. It indicated that ethanol acting on cell wall and membrane could be used as a mediator to enhance cell permeability, which facilitated the penetration of substrate across cell barrier within a short time, resulting in the elevated initial conversation rate. The observation of fatty acids composition suggested that the increased unsaturated fatty acids, especially cis-isomers, in the presence of ethanol led to the disorganization of the native arrangement of lipids and thus increased cell permeability. Our findings demonstrated that another facilitation of ethanol was to promote substrate transport into cells by permeabilization, which would provide the guidance in the practical application of organic solvents in steroid biotransformation.