The solubilisation of mycobacterium in a water in oil microemulsion for biotransformations: system selection and characterisation

The production of single enantiomer chemicals is a key research target for a wide variety of industries due to regulatory concerns over the potential toxicities of the ‘inactive’ enantiomers in racemates, together with the need for improved dosage efficiency. Enzymatic routes via specific biotransformations can, sometimes, present advantages over asymmetric chemical synthesis. However, large scale biotransformations are often constrained by practical difficulties such as: substrate solubility in aqueous systems; product inhibition, and; further metabolism of the product(s). One novel approach to minimising these problems is to encapsulate the cells in a water in oil (w/o) microemulsion which can supply substrate to cells and remove the end product while providing the cell with an aqueous environment. In this work a microemulsion system was selected to solubilise cells of a Mycobacterium sp. capable of stereospecific epoxidation. This consisted of (Tween 85 and Span 80)/n-hexadecane, and was found to give an optimum water capacity (W0=mole of water/mol of surfactant) of 25 at an hydrophilic-lipophilic balance (HLB) of the surfactant mixture of 10. The microemulsion could solubilise cell concentrations of up to 0.36 g dm−3, but this system was only stable for 2 h, while at 0.22 g dm−3 it was stable for 9 h.