We report a study on the adaptive response of a wild-type wine Saccharomyces cerevisiae strain, isolated from natural spontaneous grape must, to mild and progressive physiological stresses due to fermentation. We observed by two-dimensional electrophoresis how the yeast proteome changes during glucose exhaustion, before the cell enters its complete stationary phase. On the basis of their identification, the proteins representing the S. cerevisiae proteomic response to fermentation stresses were divided into three classes: repressed proteins, induced proteins and autoproteolysed proteins. In an overall view, the proteome adaptation of S. cerevisiae at the time of glucose exhaustion seems to be directed mainly against the effects of ethanol, causing both hyperosmolarity and oxidative responses. Stress-induced autoproteolysis is directed mainly towards specific isoforms of glycolytic enzymes. Through the use of a wild-type S. cerevisiae strain and PMSF, a specific inhibitor of vacuolar proteinase B, we could also distinguish the specific contributions of the vacuole and the proteasome to the autoproteolytic process.

The occurrence of killer yeasts in an area of Tuscany (central Italy) was studied. Killer yeasts were found in 88% of spontaneous wine fermentations from 18 wineries. The incidence of killers varied with respect to fermentation stage and vintage period, increasing from the first vintage to successive ones and from the commencement to the end of fermentation. At the end of fermentation, the proportion of killer strains relative to total yeast population was below 25% in 15 cases, above 75% in 6 cases, from 25 to 50%o in 5 cases, and from 50 to 75% in 3 cases. Karyotype analysis also showed a mixed killer population in the fermentations in which the killers dominated.

R .A . M U SM AN N O, T. D I M AG G IO AN D G. CO R AT ZA . 1999. Two different killer phenotypes were detected among K ¦ (killer) yeasts isolated from spontaneous wine fermentations using a plate bioassay. The two phenotypes differed in their degree of killer activity, and were designated as SK ¦ (strong killer) and WK ¦ (weak killer). Strains showing either phenotype were assayed for expression of killer activity under different growth conditions. Growth in must negatively affected expression of the killer activity of both phenotypes. The supernatant fluids from must cultures showed a lower killing effect than those from yeast phosphate dextrose broth (YPDB) cultures. The ability of the two K ¦ phenotypes to prevail on K-sensitive yeasts was studied in mixed-culture fermentation experiments. Under these conditions, only strains showing SK ¦ phenotype were able to prevail on the K-sensitive yeasts. These results suggest that the K ¦ phenotype could play a relevant role in spontaneous fermentations provided that the strain exhibits an SK ¦ phenotype, and that the latter phenotype should be preferred when selected K ¦ strains are to be used as fermentation starters.

Five extracts and pure compounds from the aerial parts of Hypericum triquetrifolium were tested for their antibacterial activity against 31 gram-positive and gram-negative strains using the agar dilution method (Lorian). The ethyl acetate extract exhibited a weak antibacterial activity against Staphylococcus strains, and pure constituents such as quercetin and I3,II8-biapigenin were the active components of this extract.

The EtOAc and n-BuOH extracts of Inga fendleriana inhibited Gram-positive, but not Gram-negative bacteria; a narrow spectrum of activity against Staphylococcus epidermidis was detected. The MIC values of the extracts ranged from 125 to 850 μg/mL. Quercetin 3-methylether, myricetin 3-O-rhamnoside and tricetin showed antibacterial activity against the same bacterial strains with MICs in the range from 31 to 250 μg/mL. In time-kill kinetic studies, the flavonoids showed bactericidal effects at the concentrations corresponding to four times the MICs.