Impact of high sugar content on metabolism and physiology of indigenous yeasts

Abstract

This PhD project is part of an ARC Training Centre for Innovative Wine Production larger initiative to tackle the main challenges for the Australian wine industry. In particular, the aim is to address the implication of the increasing trend of sugar accumulation in ripe grapes that consequently results in high sugar musts and high ethanol wines. These increase the risk of sluggish and stuck fermentation, especially when only the indigenous microflora of yeast is exploited. At the beginning of fermentation, yeast cells must coordinate genome expression rapidly in response to external changes to maintain competitive fitness and cell survival. Understanding how cells modulate their adaptation strategies can be the key to predicting their capacity to survive in a harsh environment and consequently be able to influence wine composition. This project aims to give strategic advice to deal with fermentations by studying non-conventional yeast physiology in response to high sugar must and correlating it with growth and metabolism. Chapter 2 compares T. delbrueckii and S. cerevisiae oenological traits at a molecular level. The mechanisms behind the metabolic differences that exist between these two species were inspected using Next Generation Sequencing technology (ILLUMINA) and analysed by assembling RNA transcriptomes. In Chapter 3 two Australian indigenous yeast species genomes were sequenced with the newest Next Generation Sequencing (NGS) technology, Nanopore MinION. Chapter 4 further analyzed the global short-term stress adaptive response to grape must, implementing the technique previously used. The results, discussed in Chapter 5, summarize the improvements in high-throughput data analysis and reveal the genomic and physiological differences of these wine-related species.