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Anti-Candida activity of a novel killer toxin from the yeast Williopsis mrakii
Abstract:
A screening of putative killer yeast strains showed that spore-forming ascomycetous yeasts of the genera Pichia and Williopsis displayed the broadest range of activity against sensitive strains of Candida spp. and Saccharomyces cerevisiae. Williopsis mrakii (NCYC 500) showed extensive anti-Candida activity against strains isolated from clinical specimens. W. mrakii killer factor was produced in minimal media as a function of growth and its activity reached constant levels as cells entered stationary phase. The proteinaceous killer toxin was found to be unstable without a specific range of temperature and pH (above 30 degrees C and pH 4.0), and further analysis showed that the active toxin molecule was an acidic polypeptide with a relative molecular mass between 1.8-5.0 kDa. At critical concentrations the killer factor exerted a greater effect on stationary phase cells of Candida than cells from an exponential phase of growth. At low concentrations, the killer toxin produced a fungistatic effect on sensitive yeasts but at higher concentrations there was evidence to suggest that membrane damage accounted for the zymocidal effects of the killer factor. the cidal nature of the toxin was reflected in a rapid decrease in sensitive cell viability. Findings presented suggest that W. mrakii killer toxin has potential as a novel antimycotic agent in combatting medically important strains of Candida.
Insights
Killer yeasts, Williopsis mrakii, produce a potent toxin effective against Candida species. This proteinaceous killer factor shows potential as a novel antimycotic agent for clinical applications.
Area of Science:
- Microbiology
- Mycology
- Biochemistry
Background:
- Killer yeasts are known to produce toxins that inhibit the growth of sensitive yeast strains.
- Candida species are significant human pathogens, causing a range of infections.
Purpose of the Study:
- To screen for killer yeast strains with broad-spectrum activity against Candida and Saccharomyces cerevisiae.
- To characterize the killer toxin produced by Williopsis mrakii and evaluate its potential as an antimycotic agent.
Main Methods:
- Screening of ascomycetous yeasts for killer activity.
- Cultivation of Williopsis mrakii in minimal media and monitoring toxin production.
- Characterization of the killer toxin's stability (temperature, pH) and molecular mass.
- Assessing the effect of the toxin on different growth phases of Candida cells.
Main Results:
- Williopsis mrakii and Pichia species exhibited broad killer activity against Candida and Saccharomyces cerevisiae.
- W. mrakii produced a proteinaceous killer toxin, stable above 30°C and pH 4.0, with a molecular mass of 1.8-5.0 kDa.
- The toxin demonstrated fungistatic effects at low concentrations and membrane-disrupting, cidal effects at higher concentrations against Candida, particularly stationary phase cells.
Conclusions:
- Williopsis mrakii killer toxin shows significant anti-Candida activity against clinical isolates.
- The toxin's characteristics suggest its potential as a novel antimycotic agent for combating medically important Candida strains.