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Varela C, Bartel C, Onetto C, Borneman A. Targeted gene deletion in Brettanomyces bruxellensis with an expression-free CRISPR-Cas9 system. Appl Microbiol Biotechnol 2020; 104:7105-7115. [DOI: 10.1007/s00253-020-10750-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 06/10/2020] [Accepted: 06/16/2020] [Indexed: 12/11/2022]
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Varela C, Bartel C, Nandorfy DE, Borneman A, Schmidt S, Curtin C. Identification of flocculant wine yeast strains with improved filtration-related phenotypes through application of high-throughput sedimentation rate assays. Sci Rep 2020; 10:2738. [PMID: 32066762 PMCID: PMC7026045 DOI: 10.1038/s41598-020-59579-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 01/30/2020] [Indexed: 11/24/2022] Open
Abstract
In most yeast-driven biotechnological applications, biomass is separated from the aqueous phase after fermentation or production has finished. During winemaking, yeasts are removed after fermentation by racking, filtration, or centrifugation, which add costs to the overall process and may reduce product yield. Theoretically, clarification and filtration can be aided through use of yeast strains that form flocs due to cell-cell binding, a process known as flocculation. However, because early flocculation can cause stuck/sluggish fermentations, this phenotype is not common amongst commercially available wine yeasts. In this study we sought to identify wine strains that exhibit late-fermentation flocculant behaviour using two complementary approaches; a high-throughput sedimentation rate assay of individual strains and a competitive sedimentation assay using a barcoded yeast collection. Amongst 103 wine strains, several exhibited strong sedimentation at the end of the wine fermentation process under various environmental conditions. Two of these strains, AWRI1688 and AWRI1759, were further characterised during red winemaking trials. Shiraz wines produced with both strains displayed improved filtration-related properties. AWRI1759 produced wines with greater filterability, whereas AWRI1688 enabled the recovery of larger wine volumes after racking. Thus, this study demonstrates the effective use of sedimentation screening assays to identify wine yeasts with practical winemaking applications.
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Affiliation(s)
- Cristian Varela
- The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide, SA, 5064, Australia. .,Department of Wine & Food Science, University of Adelaide, Glen Osmond, SA 5064, Adelaide, Australia.
| | - Caroline Bartel
- The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide, SA, 5064, Australia
| | | | - Anthony Borneman
- The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide, SA, 5064, Australia
| | - Simon Schmidt
- The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide, SA, 5064, Australia
| | - Chris Curtin
- The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide, SA, 5064, Australia.,College of Agricultural Sciences, Oregon State University, Wiegand Hall, 3051 SW Campus Way, Corvallis, OR, 97331, USA
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Inactivating Mutations in Irc7p Are Common in Wine Yeasts, Attenuating Carbon-Sulfur β-Lyase Activity and Volatile Sulfur Compound Production. Appl Environ Microbiol 2019; 85:AEM.02684-18. [PMID: 30658969 DOI: 10.1128/aem.02684-18] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 01/11/2019] [Indexed: 01/19/2023] Open
Abstract
During alcoholic fermentation of grape sugars, wine yeasts produce a range of secondary metabolites that play an important role in the aroma profile of wines. In this study, we have explored the ability of a large number of wine yeast strains to modulate wine aroma composition, focusing on the release of the "fruity" thiols 3-mercaptohexan-1-ol (3-MH) and 4-mercapto-4-methylpentan-2-one (4-MMP) from their respective cysteinylated nonvolatile precursors. The role of the yeast gene IRC7 in thiol release has been well established, and it has been shown that a 38-bp deletion found in many wine strains cause them to express a truncated version of Irc7p that does not possess cysteine-S-conjugate β-lyase activity. In our data, we find that IRC7 allele length alone does not fully explain the capacity of a strain to release thiols. Screening of a large number of strains coupled with analysis of genomic sequence data allowed us to identify several previously undescribed single-nucleotide polymorphisms (SNPs) in IRC7 that, when coupled with allele length, more robustly explain the ability of a particular yeast strain to release thiols from their cysteinylated precursors. We also demonstrate that allelic variation of IRC7 not only affects the release of thiols but modulates the formation of negative volatile sulfur compounds from the amino acid cysteine. The results of this study provide winemakers with an improved understanding of the genetic determinants that affect wine aroma and flavor, which can be used to guide the choice of yeast strains that are fit for purpose.IMPORTANCE Volatile sulfur compounds contribute to wine aromas that may be considered pleasant, such as "tropical," "passionfruit," and "guava," as well as aromas that are considered undesirable, such as "rotten eggs," "onions," and "sewer." During fermentation, wine yeasts release some of these compounds from odorless precursor molecules, a process that is most efficient when performed by yeasts that express active forms of the protein Irc7p. We show that most wine yeasts carry mutations that reduce activity of this protein, affecting the formation of volatile sulfur compounds that impart both pleasant and unpleasant aromas. The results provide winemakers with guidance on the choice of yeasts that can emphasize or deemphasize this particular contribution to wine quality.
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Morard M, Macías LG, Adam AC, Lairón-Peris M, Pérez-Torrado R, Toft C, Barrio E. Aneuploidy and Ethanol Tolerance in Saccharomyces cerevisiae. Front Genet 2019; 10:82. [PMID: 30809248 PMCID: PMC6379819 DOI: 10.3389/fgene.2019.00082] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 01/28/2019] [Indexed: 12/31/2022] Open
Abstract
Response to environmental stresses is a key factor for microbial organism growth. One of the major stresses for yeasts in fermentative environments is ethanol. Saccharomyces cerevisiae is the most tolerant species in its genus, but intraspecific ethanol-tolerance variation exists. Although, much effort has been done in the last years to discover evolutionary paths to improve ethanol tolerance, this phenotype is still hardly understood. Here, we selected five strains with different ethanol tolerances, and used comparative genomics to determine the main factors that can explain these phenotypic differences. Surprisingly, the main genomic feature, shared only by the highest ethanol-tolerant strains, was a polysomic chromosome III. Transcriptomic data point out that chromosome III is important for the ethanol stress response, and this aneuploidy can be an advantage to respond rapidly to ethanol stress. We found that chromosome III copy numbers also explain differences in other strains. We show that removing the extra chromosome III copy in an ethanol-tolerant strain, returning to euploidy, strongly compromises its tolerance. Chromosome III aneuploidy appears frequently in ethanol-tolerance evolution experiments, and here, we show that aneuploidy is also used by natural strains to enhance their ethanol tolerance.
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Affiliation(s)
- Miguel Morard
- Departament de Genètica, Universitat de València, Valencia, Spain.,Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - Laura G Macías
- Departament de Genètica, Universitat de València, Valencia, Spain.,Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - Ana C Adam
- Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - María Lairón-Peris
- Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - Roberto Pérez-Torrado
- Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - Christina Toft
- Departament de Genètica, Universitat de València, Valencia, Spain.,Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
| | - Eladio Barrio
- Departament de Genètica, Universitat de València, Valencia, Spain.,Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (IATA), CSIC, Valencia, Spain
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Cordente AG, Capone DL, Curtin CD. Unravelling glutathione conjugate catabolism in Saccharomyces cerevisiae: the role of glutathione/dipeptide transporters and vacuolar function in the release of volatile sulfur compounds 3-mercaptohexan-1-ol and 4-mercapto-4-methylpentan-2-one. Appl Microbiol Biotechnol 2015; 99:9709-22. [PMID: 26227410 DOI: 10.1007/s00253-015-6833-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 07/07/2015] [Accepted: 07/11/2015] [Indexed: 11/29/2022]
Abstract
Sulfur-containing aroma compounds are key contributors to the flavour of a diverse range of foods and beverages, such as wine. The tropical fruit characters of Sauvignon Blanc wines are attributed to the presence of the aromatic thiols 3-mercaptohexan-1-ol (3-MH), its acetate ester 3-mercaptohexyl acetate (3-MHA), and 4-mercapto-4-methylpentan-2-one (4-MMP). These aromatic thiols are not detectable in grape juice to any significant extent but are released by yeast during alcoholic fermentation. While the processes involved in the release of 3-MH and 4-MMP from their cysteinylated precursors have been studied extensively, degradation pathways for glutathione S-conjugates (GSH-3-MH and GSH-4-MMP) have not. In this study, a candidate gene approach was taken, focusing on genes known to play a role in glutathione and glutathione-S-conjugate turnover in Saccharomyces cerevisiae. Our results confirm the role of Opt1p as the major transporter responsible for uptake of GSH-3-MH and GSH-4-MMP, and identify vacuolar Ecm38p as a key determinant of 3-MH release from GSH-3-MH. ECM38 was unimportant, on the other hand, for release of 4-MMP, and abolition of vacuolar biogenesis caused an increase in the amount of 4-MMP released. The alternative cytosolic glutathione degradation pathway was not involved in release of either thiol from their glutathionylated precursors. Finally, cycling of GSH-3-MH and/or its breakdown intermediates between the cytosol and the vacuole or extracellular space was implicated in modulation of 3-MH formation. Together, these results provide new targets for development of yeast strains that optimize release of these potent volatile sulfur compounds, and further our understanding of the processes involved in glutathione-S-conjugate turnover.
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Affiliation(s)
- Antonio G Cordente
- The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia
| | - Dimitra L Capone
- The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia
| | - Chris D Curtin
- The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA, 5064, Australia.
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