14-23: Developing a whole-cell yeast biocatalyst

Several whole-cell yeast biocatalysts have been developed based on recombinant strains of Saccharomyces cerevisiae. Catalytic enzymes are produced by the yeasts and displayed on the cell surface, eliminating the need for protein purification and immobilization. The enzymes are fixed on the cell surface by one of two methods.  They may be covalently tethered to the cell wall by two disulfide bonds via an α-agglutinin fusion. Alternatively, they may adhere non-covalently through fusion with FLO1S, the truncated binding domain of an endogenous flocculation protein. Two enzymes are being investigated: lipase B from Candida antarctica (CALB, a popular industrial enzyme) and lipase from a psychrophilic bacterium, Photobacterium lipolyticum M37 (M37L). Fusion proteins are detected and quantified on the cell surface with flow cytometry. The biocatalyst demonstrates appreciable activity in aqueous and non-aqueous reactions with minimal processing after yeast cultivation. Activity is maintained over repeated batch cycles and after lyophilization, which enables long-term storage.