Sitosterol bioconversion with resting cells in liquid polymer based systems.

The use of a biocompatible water-immiscible organic phase as a substrate and product pool has been acknowledged as an effective tool to overcome the low volumetric productivity of aqueous bioconversion systems involving hydrophobic compounds. The growing environmental and public health awareness is nevertheless leading to restrictions in the use of organic solvents in industrial processes, in order to render these more environmentally friendly. Different approaches are hence being assessed for the design of alternative bioconversion media, involving the use of supercritical fluids, ionic liquids and natural oils and liquid polymers, among others. In this work, the use of liquid polymers as key components in the bioconversion media for a multi-step microbial bioconversion was assessed. The model system used was the selective cleavage of the side-chain of beta-sitosterol by free resting cells of Mycobacterium sp. NRRL B-3805, a well established industrial multi-enzymatic process involving the use of nine catabolic enzymes in a fourteen-step metabolic pathway. High product yields were obtained when silicone B oil was used as substrate carrier/product pool, both in single oil and in oil:buffer two liquid phase system.