In this work, the use of green solvents as key components in the bioconversion media for a multi-step microbial bioconversion was assessed in a suspended whole cell system, combined with the use of by-products as raw materials, ultimately used as carbon source for cell growth and as sterol substrate for bioconversion. The model system is the selective cleavage of the side-chain of β-sitosterol performed 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 14-step metabolic pathway.
Bioconversion yields in silicone media were higher than the ones obtained in polyethylene glycol (PEG), polypropylene glycol (PPG) and ionic liquids, as well as in dioctyl phthalate (DOP), an organic solvent that has previously been shown to allow high conversion yields. Total conversion of 12 mM substrate in silicone media was consistently obtained at the end of 120-h bioconversion runs. Similar bioconversion profiles were attained during a 50-fold scale-up, maintaining constant the power consumption per unit of volume.