Oenological traits of Lachancea thermotolerans show signs of domestication and allopatric differentiation
The yeast Lachancea thermotolerans (previously Kluyveromyces thermotolerans) is a species of large, yet underexplored, oenological potential. This study delivers comprehensive oenological phenomes of 94 L. thermotolerans strains obtained from diverse ecological niches worldwide, classified in nine genetic groups based on their pre-determined microsatellite genotypes. The strains and the genetic groups were compared for their alcoholic fermentation performance, production of primary and
... metabolites and pH modulation in Chardonnay grape juice fermentations. The common oenological features of L. thermotolerans strains were their glucophilic character, relatively extensive fermentation ability, low production of acetic acid and the formation of lactic acid, which significantly affected the pH of the wines. An untargeted analysis of volatile compounds, used for the first time in a population-scale phenotyping of a non-Saccharomyces yeast, revealed that 58 out of 90 volatiles were affected at an L. thermotolerans strain level. Besides the remarkable extent of intra-specific diversity, our results confirmed the distinct phenotypic performance of L. thermotolerans genetic groups. Together, these observations provide further support for the occurrence of domestication events and allopatric differentiation in L. thermotolerans population. The largely untapped biotechnological potential of yeasts other than Saccharomyces cerevisiae is triggering rising scientific interest. One remarkable example is Lachancea thermotolerans, a ubiquitous species occupying a range of anthropic and wild habitats that cover a large geographic span 1-4 . In particular, this yeast is a common constituent of grape/wine microbiota 5,6 , and has thus been explored for its application in oenology. Indeed, multiple studies have evaluated the oenological performance of L. thermotolerans isolates 7-10 delivering conclusive results; L. thermotolerans does not impart any obvious faults to the wine, rather, it can positively affect its chemical and sensory profile. In oenological environments, L. thermotolerans is a relatively robust fermenter, depending on the strain and physiochemical conditions, capable of achieving up to 13.6% (v/v) ethanol 11 . As typical for non-Saccharomyces yeasts, L. thermotolerans pure cultures cannot 'complete' wine fermentation (i.e. deplete all sugars), and therefore require sequential or simultaneous addition of another co-starter, generally an S. cerevisiae strain 5 . Due to the antagonistic activity of S. cerevisiae towards L. thermotolerans, mediated by mechanisms of cell-cell contact and secretion of antimicrobial peptides 12 , the outcomes of such co-fermentations are inoculation-dependant. The initial absence and/or lower inoculation densities of S. cerevisiae allows for the prolonged persistence and, in turn, greater metabolic contribution, of L. thermotolerans strains 9,13,14 .