Screening for suitable solvents as substrate carriers for the microbial side-chain cleavage of sitosterol using microtitre plates

The microwell-scale approach is widely used for screening purposes and one-pot biotransformations, but it has seldom been applied to whole cell multistep biotransformations and to organic solvent screening/non-conventional medium bioconversion processes, which is an issue of major relevance when bioconversion processes are addressed. The present study aims to fill in this gap by using 24-well microtitre plates as platforms for the screening of suitable organic solvents as substrate carriers for effective biocatalysis. The side-chain cleavage of sitosterol with resting cells of Mycobacterium sp. NRRL B-3805 was used as model system. Series of miscible and immiscible alcohols with primary, secondary and tertiary structure were tested as carriers of the hydrophobic substrate, thus ruling out the effect of functionality on biocatalytic activity.Results suggest that microtitre plates may be used for solvent selection in complex bioconversion systems. The highest bioconversion yields were observed when methanol and ethanol were used as substrate carriers. An empirical correlation could be established between overall catalytic activity and physicochemical properties of the solvents.