Population-wide diversity study in Lachancea thermotolerans highlights superior starters for winemaking

Abstract

Grapes from warm(ing) climates often contain excessive sugars but lack acidity. This can lead to highly alcoholic wines with compromised stability and balance. The yeast Lachancea thermotolerans can ameliorate such wines due to its metabolic peculiarity – partial fermentation of sugars to lactic acid. This study aimed to elucidate the population-wide diversity in L. thermotolerans, whilst selecting superior strains for wine sector. An extensive collection of isolates (~200) sourced from different habitats worldwide was first genotyped on 14 microsatellite loci. This revealed differentiation of L. thermotolerans genetic groups based on the isolation substrate and geography. The 94 genotyped strains were then characterised in Vitis vinifera cv. Chardonnay fermentations. The comprehensive dataset comprised microbial growth and fermentation kinetics, primary metabolites and 90 volatile compounds. The common traits of L. thermotolerans strains were their glucophilic character, relatively extensive fermentation ability (>7.3 % v/v EtOH), low production of acetic acid and formation of lactic acid. A seven-fold variation was observed in concentrations of lactate (1.8 – 12 g/L), significantly affecting the wine pH (3.2 – 3.8). Besides the strain-derived variation (significant effect on 80/114 parameters), the metabolic dataset showed separation of pre-determined L. thermotolerans genetic groups. The superior L. thermotolerans strains were further evaluated in co-inoculations and sequential inoculations with Saccharomyces cerevisiae, required for fermentation completion. The chemical and sensory modulations in wines further highlighted the potential of L. thermotolerans strains to produce ‘fresher’ wines with lower ethanol content and improved flavour/balance.