Killer yeasts produce an extracellular toxin which is lethal to other strains of yeasts, termed sensitive yeasts. Neutral yeasts are resistant to this killer factor and ...
World Journal of Microbio/ogy & Biotechnology 10, 358-359
Short Communication
Occurrence of killer yeasts in Argentine wineries F. Vazquez* and M.E. Toro Fifty-six wine must samples, from wineries in various regions of Argentina, were examined at different fermentation stages for the presence of killer yeast strains. The distribution of isolated killer strains was markedly different from one region to another. Key words: Argentina, killer yeasts, wineries.
Killer yeasts produce an extracellular toxin which is lethal to other strains of yeasts, termed sensitive yeasts. Neutral yeasts are resistant to this killer factor and do not kill sensitive cells. In Latin America, only Brazilian researchers have reported the presence of killer yeast strains in wineries (Carrau et al. 1988). This is the first report of such yeasts in Argentina.
Materials and Methods
Isolation of Yeast Strains Samples were obtained from wineries located in four Argentine provinces: Mendoza, San Juan, La Rioja and Salta. Sampling was performed in sterile conditions with musts not seeded with selected yeasts. Musts were sampled as fresh musts and at the intermediate and final stages of fermentation. The musts from which yeast strains were isolated belonged to 17 grape varieties. Detection of Killer and Sensitive Character The yeasts were characterized according to Sommers & Bevan (1969) at pH 3.5 or 4.5. Three assays under identical conditions were carried out for each strain. The reference yeasts used to verify killer and sensitive effects in the isolated strains were, respectively, ATCC 36900 (NCYC 738) and NCYC 1006.
Results and Discussion The killer-sensitive interactions were observed only among yeast strains belonging to the Saccharomyces genus (Kregervan Rij 1984). Results are shown in Tables 1 and 2. Of the 56 musts examined, 16 contained killer yeast strains. The occurrence of killer yeasts differed markedly from one region to another. The highest frequency of killer yeasts was in San Juan (33%) and no such yeasts were found in Salta. A similar patchy distribution was observed in France by Cuinier & Gros (1983). Reports from Brazil on killer yeasts (Carrau et al. 1988) showed variable frequencies but none lower than 28%. Cuinier & Gross (1983) and Carrau et al. (1988) found that most of their strains were neutral and killer. However, in three Argentinian provinces out of the four surveyed, sensitive yeasts were dominant in the wine musts. Killer yeast strains were isolated at every fermenting stage (Table 2). The fre-
Table 1. Characteristics of yeast strains isolated from Argentine wine musts Origin
Salta La Riga San Juan Mendoza
No. of samples
Frequency of yeast (%)
No. of samples Sensitive with killer yeast strains
Killer
Neutral
8
0
7
19
18 38
82 44
2
28 13
33 8
51 17
16 75
12 2
0
Killer yeasts in Argentine wineries Table 2. Charecterlatlcs of the yeast strains Isolated from Argentine wine musts st different stages of fermentation Fermentation No. of stage samples
