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Pore formation on proliferating yeast Saccharomyces cerevisiae cell buds by HM-1 killer toxin
T Komiyama1, T Ohta, H Urakami
1Department of Biochemistry, Niigata College of Pharmacy. komiyam@niigata-pharm.ac.jp
Abstract:
The cytocidal effect of HM-1 produced by Hansenula mrakii on yeast Saccharomyces cerevisiae cells was studied. The HM-1 strongly inhibited the growth of S. cerevisiae cells at a low concentration (IC50: 2.1 x 10(-8) M) by reducing the number of viable cells. The killer action of HM-1 was most efficient when cells were actively proliferating. Cells in a resting state were resistant, but they became HM-1-sensitive after about 90 min of culturing at 30 degrees C, concomitantly with the increment of budding index. In association with the reduction of viable cell number, ultraviolet light-absorbing cellular components were discharged from sensitive cells. HM-1 molecules appear to bind to susceptible cells rather loosely since cells incubated with HM-1 were able to proliferate after having been washed. By phase-contrast light microscopy and scanning electron microscopy, discharge of cell material was observed at the budding portions of HM-1-treated cells. Addition of sorbitol to make the culture medium isotonic partially reduced the cell death induced by HM-1. These results suggest that HM-1 acts on the budding region of proliferating yeast cells, resulting in pore formation, leakage of cell material and eventual cell death.
Insights
The yeast killer toxin HM-1 from Hansenula mrakii effectively inhibits Saccharomyces cerevisiae growth by targeting actively proliferating cells. This toxin causes cell death by inducing pore formation and material leakage, particularly at budding sites.
Area of Science:
- Mycology
- Cell Biology
- Biochemistry
Background:
- Hansenula mrakii produces a killer toxin, HM-1, with known antimicrobial properties.
- Yeast killer toxins are proteins that exhibit toxicity against sensitive yeast strains.
- Understanding the mechanism of action of yeast killer toxins is crucial for their potential applications.
Purpose of the Study:
- To investigate the cytocidal effect of HM-1 on Saccharomyces cerevisiae.
- To determine the mechanism by which HM-1 inhibits yeast cell growth.
- To identify the specific cellular targets and processes affected by HM-1.
Main Methods:
- Growth inhibition assays to determine IC50 values.
- Cellular viability studies under various conditions.
- Microscopy techniques (phase-contrast and scanning electron microscopy) to observe cellular changes.
- Treatment with sorbitol to assess the role of osmotic pressure.
Main Results:
- HM-1 exhibited strong growth inhibition of S. cerevisiae at low concentrations (IC50: 2.1 x 10(-8) M).
- Killer activity was highest in actively proliferating cells, while resting cells showed resistance.
- HM-1 treatment led to the discharge of UV-absorbing cellular components and cell material from budding regions.
- Cell death was partially reduced by isotonic conditions, suggesting a role for osmotic stress.
Conclusions:
- HM-1 acts on the budding region of proliferating yeast cells.
- The toxin induces pore formation, leading to leakage of cellular material and cell death.
- HM-1's mechanism involves targeting actively dividing cells and potentially disrupting cell wall integrity.