Putting microbial diversity to work in shaping wine style
The AWRI has a long history in microbial strain development and the successful deployment and commercialisation of newly-developed strains. This project aims to build on that history.
There is substantial scope to both refine existing strains (such as the ‘rose’ yeast and Saccharomyces bayanus hybrids) and optimise their use through varietal or wine style pairing. For example, building on knowledge gained through production of the ‘rose’ yeast, this project will explore the degree to which yeast aromatic profiles can be modulated by modification of carbon flux through amino acid biosynthetic pathways.
Molecular technology will help to determine what is possible, and will provide foundational knowledge on biosynthetic pathways and markers for strain selection. Identification of molecular markers for specific aromatic traits will permit targeted selection of strains isolated during bioprospecting work.
In addition, this project will tap into resources identified in other AWRI projects that have a bioprospecting focus. Novel microorganisms, after initial screening, will be put to work directly through use of appropriate winemaking techniques and/or be used as source material for introducing greater genetic diversity into existing wine strains. Together these breeding and selection strategies will deliver non-genetically modified germplasm that can be used by industry, and will provide new microorganisms for winemakers seeking a point of differentiation in their wines.
Production of yeasts that enhance ‘floral’ characteristics of wine
Through the targeted use of amino acid analogues, it was possible to isolate a wine yeast that substantially overproduced 2-phenylethanol and 2-phenylethyl acetate (Cordente et al. 2018) and hence produced wines with enhanced ‘floral’ characteristics. However, the high concentrations of 2-phenylethanol and the associated tryptophol and tyrosol produced by this yeast were only suited to the production of a narrow range of wines. Work in the past year has focused on yeasts producing intermediate concentrations of 2-phenylethanol and 2-phenylethyl acetate. These yeasts not only produced different concentrations of these ‘floral’ aroma compounds but produced them in different ratios and with different concentrations of tryptophol and tyrosol. These strains were evaluated at pilot scale during the 2018 vintage and sensory and chemical analysis are scheduled for later in the year. It is hoped that they will both expand the range of wines for which ‘floral’ aromatic enhancement can be used and also shed light on yeast secondary metabolism and the production of indole-related metabolites and their oenological qualities.
Bringing stability to hybrid yeasts
The bringing together of two different species of yeast, as occurs during the production of interspecific hybrids through rare mating, can expose genomic incompatibilities, with genomic instability often the result. Genomic incompatibilities can cause the seemingly random loss of sometimes large genetic elements during propagation, and with this loss comes the potential for loss of desirable traits. A program of adaptive conditioning of an F1 hybrid (a child of two parents) was undertaken using serial fermentation of Chardonnay (Bellon et al. 2018). Analysis of chromosomal loss at the end of each fermentation in the series revealed loss of S. uvarum chromosome 14 to be the most prominent alteration, and this occurred early in the series. In short, genome stabilisation happened quickly, with subsequent genetic alterations representing sporadic events that did not propagate through the population. The advantage of this approach is that traits critical for performance during fermentation of grape juice are perpetuated while ensuring that strains resulting from this process are able to be propagated without further loss of critical genomic elements.
A vintage trial comparing a large group of interspecific hybrids, all products of rare mating with diverse non-cerevisiae species, was undertaken in 2018. This is the first ‘head-to-head’ comparison of such a diverse array of hybrids and will provide a robust understanding of the different characters that diversifying the genetic basis of S. cerevisiae can bring to wine.
Bellon, J.R., Ford, C.M., Borneman, A.R., Chambers, P.J. 2018. Improved industrial interspecific wine yeasts using chromosomal mutations as potential makers for increased fitness. Front. Microbiol. 9(1442): 1-12.
Cordente, A.G., Solomon, M., Schulkin, A., Francis, I.L., Barker, A., Borneman, A.R., Curtin, C.D. 2018. Novel wine yeast with ARO4 and TYR1 mutations that overproduce ‘floral’ aroma compounds 2-phenylethanol and 2-phenyethyl acetate. Appl. Microbiol. Biotechnol. 102(14): 5977-5988.