Characterisation of yeast genes involved in flavour determination in wine.
Kate Howell (1), Mathias Klein (2), Jan H Swiegers (1), Yoji Hayasaka (1), Gordon M Elsey (3), Graham H Fleet (4), Peter B Høj (5), Isak S Pretorius (1), Paul Chambers (1), Miguel A de Barros Lopes (6)
(1) Biosciences Group, Australian Wine Research Inst., PO Box 197, Glen Osmond, Adel, SA, 5064, Australia; (2) Present address, Department of Biotechnology, Aachen University of Technology (RWTH), D-52074 Aachen, Germany; (3) School of Chemistry, Physics and Earth Sciences, Flinders University, GPO Box 2100, Adelaide SA 5100, Australia; (4) Food Science and Technology, School of Chemical Engineering and Industrial Chemistry, University of New South Wales, Sydney NSW 2052, Australia; (5) Present address:, The Australian Research Council, GPO Box 2702 Canberra ACT 2601 Australia; (6) Present address, School of Pharmacy and Medical Sciences, University of South Australia, GPO Box 2471, Adelaide SA 5001, Australia
The volatile thiol 4-mercapto-4-methylpentan-2-one (4MMP) is a potent contributor to wine aroma. In grape juice, 4MMP is bound to cysteine as a non-volatile compound and requires the action of a carbon sulfur lyase for its release during fermentation. This enzyme activity is provided by wine yeast. To establish the mechanism of 4MMP release, and to develop strains that are able to modulate its release, the effect of deleting genes encoding putative yeast carbon sulfur lyases on the cleavage of Cys-4MMP was tested. This led to the identification of four genes that influence the release of 4MMP in a laboratory strain, indicating that the mechanism of release may involve multiple genes. Deletion of the same genes in a homozygous derivative of the commercial wine yeast, VL3, confirmed the importance of these genes in 4MMP release. Interestingly, a yeast strain with a deletion in a putative carbon sulfur lyase gene, YAL012w, was found to produce increased levels of another sulfur compound, 2-methyltetrathiophen-3-one (MTHT). While this compound had previously been shown to contribute to wine aroma its source was unknown. The increased level of production of MTHT in the yal012w Δ strain relative to the parent suggests a role for yeast in generating this aroma compound.