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Yeasts population associated with grapes from Northwest Argentina, a region with a significant vine-growing increase over the past years, was evaluated. Ten species of non-Saccharomyces yeasts were identified from four grape varieties (Malbec, Merlot, Syrah and Torrontes) being Hanseniaspora uvarum the dominant species. Typing of isolates revealed genetic variability within Hanseniaspora genus and also high variability was observed according to their oenological characteristics. Based on the oenological properties, the most adequate strains as starter cultures were H. uvarum HuT7, HuMe15, HuS16, H. vineae HvT-mc1 and Metschnikowia pulcherrima MpT2/MpT3. These selected yeasts exhibited moderate resistance to SO2, reduced values of volatile acidity, null or low production of H2S, high levels of enzymes related to aroma and did not produce killer toxins. Further studies using mixed cultures of these non-Saccharomyces strains and S. cerevisiae are needed to validate the contribution of selected indigenous yeasts on wine organoleptic characteristics. [ABSTRACT FROM AUTHOR]

The yeast Hanseniaspora uvarum liberates a killer toxin lethal to sensitive strains of the species Saccharomyces cerevisiae. Secretion of this killer toxin was inhibited by tunicamycin, an inhibitor of N-glycosylation, although the mature killer protein did not show any detectable carbohydrate structures. Culture supernatants of the killer strain were concentrated by ultrafiltration and the extracellular killer toxin was precipitated with ethanol and purified by ion exchange chromatography. SDS-PAGE of the electrophoretically homogenous killer protein indicated an apparent molecular mass of 18,000. Additional investigations of the primary toxin binding sites within the cell wall of sensitive yeast strains showed that the killer toxin of Hanseniaspora uvarum is bound by β-1, 6- d-glucans. [ABSTRACT FROM AUTHOR]

By heat treatment killer strains of the type K1 of Saccharomyces cerevisiae that are known to harbour dsRNA plasmids were completely cured, whereas only a small fraction of the clones of the killer type K2 had lost the dsRNA dependent killer character. The K2 killers but not the strains of killer type K1 were easily cured by cycloheximide. Killer strains of Hanseniaspora uvarum were not curable by heat treatment. Curing was successfull with cycloheximide or 5-fluorouracil. Two double-stranded RNA plasmids were detected in the killer strains of H. uvarum. The smaller dsRNA plasmid was absent in the strains that were cured of their killer character by 5-fluorouracil. The killer character of H. uvarum was transferred to S. cerevisiae by spheroplast fusion. The fusion products showing the killer character contained both dsRNA plasmids, obviously the smaller plasmid (M-dsRNA) carries the genes for killer toxin formation. Killer strains of Pichia kluyveri were not curable of their killer character, in these strains no dsRNA plasmids were detected. [ABSTRACT FROM AUTHOR]