Yeasts killer/sensitivity phenotypes and halotolerance

Abstract

Yeast killer phenotype is not uniformly distributed within certain genera or even within some species. Salt has been described as enhancing killer action, especially in strains that have been isolated from salt environments. The aim of this work was to evaluate the extent of the correlation, if any, between killer/sensitivity and salt-stress tolerance phenotypes. A set of 58 different yeast strains (46 species) was studied. As it has been previously described, tolerance to salt stress can be classified in four major classes of tolerance: 1, 2, 3 and 4 M NaCl. Investigation of killer and sensitivity phenotypes was carried out in the absence and in the presence of NaCl from 0 to 3.5 M, in 0.5 M increments. On the basis of this study, two different groups of yeasts were established. One group was mainly composed of the more halotolerant killer yeasts, which also displayed an increase of killer spectrum in the presence of salt in the assay. The other group included the less halotolerant strains, whose killer spectrum was less significant and either did not vary consistently with salt stress in the assay or decreased in its presence. Although killer activity was found in yeasts belonging to the various classes of salt-stress tolerance, the percentage of strains showing this capacity increased significantly for the classes of higher halotolerance, while the percentage fraction of sensitive strains remained approximately constant. This suggests a phenotypic relationship between high halotolerance and killer capacity manifestation in the presence of high salt concentrations, which is not a consequence of an increase in sensitivity to salt stress of the target strains.

Fenotip ubilačkog kvasca nije jednoliko rasprostranjen unutar određenih vrsta ili čak unutar nekoga soja. Poznato je da sol pojačava ubilačko djelovanje, osobito onih sojeva izoliranih iz slanog okoliša. U ovom se radu nastojao procijeniti stupanj korelacije (ako postoji) između osjetljivosti ubilačkih svojstava te otpornosti prema soli pojednih fenotipova. Kao što je prije opisano, proučena je osjetljivost prema soli 58 različitih sojeva kvasca (46 vrsta). Kvasci su prema osjetljivosti razvrstani u četiri glavne skupine, a rast je utvrđen pri 1, 2, 3 i 4 M NaCl. Ispitivanje ubilačkih svojstava i osjetljivosti fenotipova provedeno je u odsutnosti i prisutnosti NaCl, u rasponu od 0 do 3,5 M, s porastom od 0,5 M. Utvrđene su dvije različite skupine kvasaca. Jedna je uglavnom bila sastavljena od ubilačkih kvasaca jače otpornih na sol, koji su pokazivali povećane ubilačke sposobnosti u prisutnosti soli. Druga je pak obuhvaćala sojeve manje otporne na sol, čija su ubilačka svojstva bila manje izražena, a nisu se bitno mijenjala u prisutnosti soli ili su se čak smanjivala. Određujući otpornost na sol uočeno je ubilačko svojstvo kvasaca koji pripadaju raznim razredima. Postotak sojeva koji su imali to svojstvo bitno je porastao kod onih s većom otpornosti prema soli, dok je postotak osjetljivih sojeva ostao približno konstantan. To upućuje na to da postoji fenotipski odnos između velike otpornosti prema soli i pojave ubilačkih svojstava uz veliki udjel soli, što nije posljedica povećane osjetljivosti sojeva prema stresu u prisutnosti soli.