Optimization of killer assays for yeast selection protocols

LOPES C.A.; SANGORRÍN M.P.

REVISTA ARGENTINA DE MICROBIOLOGíA

ASOCIACION ARGENTINA MICROBIOLOGIA

Año: 2010 vol. 42 p. 298 - 306

0325-7541

A new optimized semi-quantitative yeast killer assay is reported for the first time.The killer activity of 36 yeast isolates belonging to three species namely: Metschnikowiapulcherrima, Wickerhamomyces anomala and Torulaspora delbrueckii was tested with aview to the potential use of these yeasts as biocontrol agents against the wine spoilagespecies Pichia guilliermondii and P. membranifaciens.The effectiveness of the classical stike-based technique (qualitative method) andthe new semi-quantitative one was compared. The percentage of yeasts showing killeractivity was found to be higher by the semi-quantitative (60%) than by the qualitativemethod (45%). In all cases, the addition of 1% NaCl into the medium allowed a betterobservation of killer phenomenon.Important differences were observed in the killer capacity of different isolatesbelonging to a same killer species. The broadest spectrum of action was detected in isolates W. anomala NPCC 1023 and 1025, and M. pulcherrima NPCC 1009 and 1013.We also brought experimental evidence supporting the importance of the adequateselection of the sensitive isolate to be used in killer evaluation.The new semi-quantitative method proposed in this work enables to visualize therelationship between the number of yeasts tested and the growth of the inhibition halo(specific productivity). Hence, this experimental approach could become an interestingtool to be taken into account for killer yeast selection protocols.