Winemaking and bioprocesses strongly shaped the genetic diversity of the ubiquitous yeast Torulaspora delbrueckii

Diversity of yeast strains of the genus Hanseniaspora in the winery environment: What is their involvement in grape must fermentation?

Isolated yeast populations of Chardonnay grape must during spontaneous fermentation were compared to those isolated on grape berries and in a winery environment before the arrival of the harvest (air, floor, winery equipment) and in the air through time. Two genera of yeast, Hanseniaspora and Saccharomyces, were isolated in grape must and in the winery environment before the arrival of the harvest but not on grape berries. The genus Hanseniaspora represented 27% of isolates in the must and 35% of isolates in the winery environment. The isolates of these two species were discriminated at the strain level by Fourier transform infrared spectroscopy. The diversity of these strains observed in the winery environment (26 strains) and in must (12 strains) was considerable. 58% of the yeasts of the genus Hanseniaspora isolated in the must corresponded to strains present in the winery before the arrival of the harvest. Although the proportion and number of strains of the genus Hanseniaspora decreased during fermentation, some strains, all from the winery environment, subsisted up to 5% ethanol content. This is the first time that the implantation in grape must of populations present in the winery environment has been demonstrated for a non-Saccharomyces genus.

TdPIR minisatellite fingerprinting as a useful new tool for Torulaspora delbrueckii molecular typing

Torulaspora delbrueckii yeast strains are being increasingly applied at the industrial level, such as in the winemaking process, and so their identification and characterisation require effective, fast, accurate, reproducible and reliable approaches. Therefore, the development of typing techniques that allow discrimination at the strain level will provide an essential tool for those working with T. delbrueckii strains. Here, 28 T. delbrueckii strains from various substrates were characterised using different PCR-fingerprinting molecular methods: random amplified polymorphic DNA with polymerase chain reaction (RAPD-PCR), minisatellites SED1, AGA1, DAN4 and the newly designed T. delbrueckii (Td)PIR, and microsatellites (GAC)5 and (GTG)5. The aim was to determine and compare the efficacies, reproducibilities and discriminating powers of these molecular methods. RAPD-PCR using the M13 primers and the newly designed TdPIR3 minisatellite primer pair provided discrimination of the greatest number of T. delbrueckii strains. TdPIR3 clustered the 28 strains into 16 different groups with an efficiency of 100%, while M13 clustered the strains into 17 different groups, although with a lower efficiency of 89%. Moreover, the TdPIR3 primers showed reproducible profiles when the stringency of the PCR protocol was varied, which highlighted the great robustness of this technique. In contrast, variation of the stringency of the M13 PCR protocol resulted in modification of the amplified profiles, which suggested low reproducibility of this technique.