The yeast flora associated with the surface of grapes during ripening was studied with regard to different sectors of the grape skin and the position in the bunch by means of traditional as well as more vigorous preisolation and precounting treatments. The yeast number per square centimeter of skin increases with ripening and is highest in the area immediately surrounding the stem. The cluster sector closer to the peduncle seems to constitute a favorable substrate for yeasts, hosting a resident flora about 10 and 100 times higher than the central and lower parts of the bunch, respectively.Kloeckera apiculata was the normal resident species of grapes regardless of the sector or the ripening period, and constitutes the fermenting flora of mature grapes. The ecological implications of the results of this survey are discussed.

Strains of the genera Saccharomyces, Saccharomycodes, Schizosaccharomyces, Hanseniaspora, Kluyveromyces, Pichia, Kloeckera, and Torulopsis were examined for killer, sensitive, neutral, and killer-sensitive characteristics against a killer strain (NCYC738) and a sensitive strain (NYCC1006) of Saccharomyces cerevisiae. Thirty-one Saccharomyces cerevisiae strains out of 782 screened were able to kill the sensitive test strain; 707 appeared to be sensitive and 44 neutral. A high frequency of killer phenotypes (71.4%) was found in Hansenula anomala var. anomala strains. No killer strains were present in the remaining 17 species considered.

The yeast flora associated with the surface of various natural materials have been studied on the assumption that individual cells and microcolonies are strongly retained by gummy and mucous secretions. Preisolation treatments based on vigorous shaking, percolation with an excess of water, and the sonication of samples allowed the recovery of a much higher number of species than did traditional isolation procedures. Results confirmed that a sequence of aggressive and disruptive actions on samples, together with an enrichment culture, is necessary to obtain an exhaustive picture of the actual yeast flora.

No abstract

No abstract

The cross-reaction between 6 killer strains of Saccharomyces cerevisiae and 41 killer strains of Hansenula anomala var. anomala was examined. Fifteen strains of Hansenula killed one or more cultures of S. cerevisiae. None of the killer strains of H. anomala var. anomala was killed by S. cerevisiae killer strains or by killer strains of the same species. In S. cerevisiae different killer toxin and immunity systems were represented. Intraspecific killing activity was not found among the 41 strains of H. anomala var. anomala.

No abstract

The screening for ‘killer’ character among 23 strains of the genus Kluyveromyces showed the presence of three ‘killer’ strains (K. phaffii; K. vanudenii and K. wikenii). Their ‘killer’ activity against yeasts of other genera is in agreement with the results of others studies. Particularly K. phaffii inhibited many strains of Kloeckera apiculata.