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Applied and Environmental Microbiology, September 2005, p. 5420-5426, Vol. 71, No. 9
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.9.5420-5426.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Genetic Determinants of Volatile-Thiol Release by Saccharomyces cerevisiae during Wine Fermentation
Kate S. Howell,1,2 Mathias Klein,3 Jan H. Swiegers,1 Yoji Hayasaka,1 Gordon M. Elsey,1,4 Graham H. Fleet,2 Peter B. Høj,1 Isak S. Pretorius,1* and Miguel A. de Barros Lopes1,5The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, South Australia 5064, Australia,1 Food Science and Technology, School of Chemical Engineering and Industrial Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia,2 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, South Australia 5100, Australia,4 School of Pharmacy and Medical Sciences, University of South Australia, GPO Box 2471, Adelaide, South Australia 5001, Australia5
Received 14 December 2004/ Accepted 14 April 2005
Volatile thiols, particularly 4-mercapto-4-methylpentan-2-one (4MMP), make an important contribution to the aroma of wine. During wine fermentation, Saccharomyces cerevisiae mediates the cleavage of a nonvolatile cysteinylated precursor in grape juice (Cys-4MMP) to release the volatile thiol 4MMP. Carbon-sulfur lyases are anticipated to be involved in this reaction. To establish the mechanism of 4MMP release and to develop strains that modulate its release, the effect of deleting genes encoding putative yeast carbon-sulfur lyases on the cleavage of Cys-4MMP was tested. The results led to the identification of four genes that influence the release of the volatile thiol 4MMP in a laboratory strain, indicating that the mechanism of release involves multiple genes. Deletion of the same genes from a homozygous derivative of the commercial wine yeast VL3 confirmed the importance of these genes in affecting 4MMP release. A strain deleted in a putative carbon-sulfur lyase gene, YAL012W, produced a second sulfur compound at significantly higher concentrations than those produced by the wild-type strain. Using mass spectrometry, this compound was identified as 2-methyltetrathiophen-3-one (MTHT), which was previously shown to contribute to wine aroma but was of unknown biosynthetic origin. The formation of MTHT in YAL012W deletion strains indicates a yeast biosynthetic origin of MTHT. The results demonstrate that the mechanism of synthesis of yeast-derived wine aroma components, even those present in small concentrations, can be investigated using genetic screens.
* Corresponding author. Mailing address: The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA 5064, Australia. Phone: 61-8-83036600. Fax: 61-8-83036601. E-mail: Sakkie.Pretorius{at}awri.com.au.
Applied and Environmental Microbiology, September 2005, p. 5420-5426, Vol. 71, No. 9
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.9.5420-5426.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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