Treatment of yeast cells by electric field

Abstract

Saccharomyces cerevisiae (S. cerevisiae) – is a simple eukaryote cell, which serves as a model system for eukaryotes, as it is homologous to animal and plant cells, periodically used for studying fundamental cellular processes [1]. Yeast cells can be used as a bioreceptor in biosensors [1, 2]. Scanning electrochemical microscopy (SECM) provides the means to monitor cells in the specialized medium using non-invasive methods. SECM can be used to investigate changes in biosensors’ surface and to determine their reaction to different changes in the surrounding conditions, such as mediators and the effect of a temporary electric field. Atomic force microscopy (AFM) provided valuable information about the cell’s surface changes e.g. shape, size or any deformability induced in the cell’s membrane, the cytoskeleton and the cytosol. From force-distance curves, measured by AFM, it is possible to get additional information about the physical properties of biological samples, such as Young’s modulus and adhesion forces [3]. The influence of mediators and additionally applied electric field on cell viability can be determined from morphological data. The plasma membrane protects the cell from an outside environment and ensures its homeostasis. Yeast cells affected by an electric field could form hydrophilic or non-hydrophilic pores in the membrane, it may increase transportation of compounds which are usually not supposed to be transported to the inside of the cell. A study was conducted using a double mediator based system, lipophilic, which takes part in redox reactions inside the cell with NAD, NADP and many others, a hydrophilic mediator which is the final electron acceptor [1]. From the mediators used in the study the most effective for SECM cell imaging was found to be 9,10-phenanthraquinone (PQ), which acts as a second redox mediator in the charge transfer chain of yeast cells, when ferricyanide is used as a first redox mediator [2]. The UME current, measured with PQ as a second redox mediator, was more than 3 times higher than with other evaluated hydrophilic redox mediators. Therefore, the toxicity of PQ is also 3 times higher than other redox mediators. Yeast cells, affected by PQ, were measured by AFM in contact mode. The results show, that after exposure with 0.05 mM PQ, cell morphology was not greatly affected, but an increase in cells’ surface roughness was observed. After a second exposure with the same conditions, the cell’s surface appears smoother, which is a sign of decreased cell viability. Therefore, SECM and AFM are suitable for researching the effects of toxicity. Furthermore, going to continue investigation of the electric field application and its effects on yeast cell.