Genetic characterization of strains of Saccharomycescerevisiae responsible for 'refermentation' in Botrytis-affected wines.
OBJECTIVE
Saccharomyces cerevisiae is responsible for alcoholic fermentation of wines. However, some strains can also spoil sweet Botrytis-affected wines. Three 'refermentation' strains were isolated during maturation. Characterization of those strains in regards to their fingerprint, rDNA sequence and resistance to SO2, which constituted the main source of stress in Botrytis-affected wines, was carried out.


RESULTS
Refermentation strains could be clearly discriminated by interdelta fingerprinting. However, they exhibited close relationships by karyotyping. A part of RDN1 locus sequence was examined by using PCR-RFLP and PCR-DGGE. The resistance of refermentation strains to SO2 was performed by using real time quantitative PCR focusing on SSU1 gene.


CONCLUSIONS
Results suggested that refermentation strains were heterozygote in 26S rDNA and their ITS1-5.8S rDNA-ITS2 region sequence revealed relationships with 'flor' strains. As described in the literature for flor strain, two out of three refermentation strains constitutively developed a higher level of SSU1 expression than the reference strains, improving their putative tolerance to SO2. Therefore, refermentation strains of S. cerevisiae had developed many strategies to survive during maturing sweet wines.


CONCLUSIONS
Singularities in rDNA sequence and SSU1 overexpression revealed a natural adaptation. Moreover, genomic relationship between flor and refermentation strains suggested that stress sources could induced selection of survivor strains.
Divol
B
B
UMR oenologie-ampélologie, INRA--culté d'oenologie, Université Victor Segalen, Bordeaux 2, France.
Miot-Sertier
C
C
Lonvaud-Funel
A
A
D000079:Acetaldehyde / Q000032:analysis; D027321:Anion Transport Proteins / Q000235:genetics; D000975:Antioxidants / Q000494:pharmacology; D020171:Botrytis / Q000502:physiology*; D003470:Culture Media; D004271:DNA, Fungal / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D025141:Drug Resistance, Fungal / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D005285:Fermentation; D005516:Food Microbiology; D005800:Genes, Fungal / Q000235:genetics; D006579:Heterozygote; D019901:Locus Control Region / Q000235:genetics; D016533:Mycological Typing Techniques / Q000379:methods; D016133:Polymerase Chain Reaction / Q000379:methods; D012150:Polymorphism, Restriction Fragment Length; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000302:isolation & purification; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D013458:Sulfur Dioxide / Q000494:pharmacology; D014920:Wine / Q000382:microbiology*
D027321:Anion Transport Proteins; D000975:Antioxidants; D003470:Culture Media; D004271:DNA, Fungal; D004275:DNA, Ribosomal; D029701:Saccharomyces cerevisiae Proteins; C108311:Ssu1 protein, S cerevisiae; D013458:Sulfur Dioxide; D000079:Acetaldehyde