CENTRO DE REFERENCIA PARA LACTOBACILOS
Unidad Ejecutora - UE
Killer phenotype determination of wine yeasts
LUCÍA M. MENDOZA; MARÍA C. MANCA DE NADRA; MARTA E. FARÍAS
Lugar: Mendoza, Argentina; Año: 2007
An inhibitory mechanism, which can occur in wine fermentations, is the so-called yeast killer activity. Killer yeasts have the intrinsic ability to kill sensitive yeasts by secreting a proteinaceous toxin to which they themselves are immune. We investigated the killer activity of Kloeckera apiculata mc1 and Saccharomyces cerevisiae mc2 and determined if the toxin production was involved in the diminution of maximum cell population in mixed culture. The tests were performed in plates of YPD medium containing 0.03 g/l methylene blue and 0.1 M citrate-phosphate buffer at different pH values (pH 3.5, 4.5 and 5). Strains are scored as killers when the inoculated strain on the lawn sensitive yeast is surrounded by a clear zone of inhibition fringed with blue colour. The sensitive character was detected inoculating killer reference strains on the lawn of the strains to be tested. The strain that did not respond to both reference strains was considered as neutral. The plates were incubated 3-5 days at 18 ºC. S. cerevisiae mc2 was killer sensitive against the reference killer toxins and K. apiculata was killer neutral. Additionally, none of the strains were killer positive towards the killer sensitive strain. The variation of pH from 3.6 to 5.0 did not bring about different results. When S. cerevisiae was seeded on K. apiculata lawn a zone of inhibition could be observed, but no ring of dead cells is present, indicating that the inhibition may be produced by metabolites other than yeast killer toxins.