Biology of killer yeasts

Abstract

Killer yeasts secrete proteinaceous killer toxins lethal to susceptible yeast strains. These toxins have no activity against microorganisms other than yeasts, and the killer strains are insensitive to their own toxins. Killer toxins differ between species or strains, showing diverse characteristics in terms of structural genes, molecular size, mature structure and immunity. The mechanisms of recognizing and killing sensitive cells differ for each toxin. Killer yeasts and their toxins have many potential applications in environmental, medical and industrial biotechnology. They are also suitable to study the mechanisms of protein processing and secretion, and toxin interaction with sensitive cells. This review focuses on the biological diversity of the killer toxins described up to now and their potential biotechnological applications.

Antagonistic yeasts competes for iron with winter wheat stem base pathogens

“…Yao and Tian (2005) applied the antagonist Cryptococcus laurentii to control postharvest diseases (Monilinia fructicola and Penillium expansum) in peach fruit. The cited authors noted the maximum activity levels of 1,3-glucanase and peroxidase (POD) and enhanced effects of yeasts fungi have been also observed in previous research (Marquina et al 2002;Walker et al 1995;Vero et al 2009). The studies of other authors have shown that A. pullulans isolates may produce the enzymes glucanase and chitinase in the presence of Penicillium expansum cell walls (Vero et al 2009).…”

Characterization of some indigenousSaccharomyces cerevisiaeisolates obtained during vinification of ‘Kalecik Karasi’ and ‘EMIR’ grapes grown in Central Anatolia

“…These phenotypes are: killer (K); killer-sensitive (K-S); sensitive (S); neutral (N) (Delfini and Formica, 2001). Several killer toxin types has been described for S. cerevisiae, however K2-type toxin has proved to be the most important one in winemaking because it is active at pH values during wine production (Marquina et al, 2002). In the present study, it was found that ten S. cerevisiae isolates were sensitive, four isolates were neutral, five isolates were killer-sensitive and only one isolate was killer (Table V).…”

Mycoviruses: future therapeutic agents of invasive fungal infections in humans?

“…In the search for novel and more selective antifungal agents, fungal cell wall components represent primary targets, as these structures are restricted to yeasts and higher fungi and do not occur in human cells [44,45]. Each of the mentioned cell wall components has been shown to act as the primary binding site for different yeast killer toxins [46][47][48][49]. In addition, for killer toxins secreted by various strains of the yeast Hansenula it was demonstrated that these toxins not only bind to yeast cell wall components, but that they also strongly inhibit de novo L-1,3-D-glucan biosynthesis [50,51].…”

“…These derivatives have shown activity against various human fungal pathogenic fungi including C. albicans and may be therapeutic when administered parentally. For reviews of killer toxin/antibodies the reader is referred to Marquina et al [49], Magliani et al [55], and Schmitt and Breinig [40].…”