Bioelectrochemistry (v.64, #2)

Techniques of signal generation required for electropermeabilization by Marko Puc; Selma Čorović; Karel Flisar; Marko Petkovšek; Janez Nastran; Damijan Miklavčič (113-124).
Electropermeabilization is a phenomenon that transiently increases permeability of the cell plasma membrane. In the state of high permeability, the plasma membrane allows ions, small and large molecules to be introduced into the cytoplasm, although the cell plasma membrane represents a considerable barrier for them in its normal state. Besides introduction of various substances to cell cytoplasm, permeabilized cell membrane allows cell fusion or insertion of proteins to the cell membrane. Efficiency of all these applications strongly depends on parameters of electric pulses that are delivered to the treated object using specially developed electrodes and electronic devices—electroporators. In this paper we present and compare most commonly used techniques of signal generation required for electropermeabilization. In addition, we present an overview of commercially available electroporators and electroporation systems that were described in accessible literature.
Keywords: Electroporation; Electropermeabilization; Instrumentation; Electrochemotherapy; Gene transfection;

Electrochemical investigation of the dynamics of Mycobacterium smegmatis cells' transformation to dormant, nonculturable form by B.A Kuznetsov; M.E Davydova; M.O Shleeva; S.V Shleev; A.S Kaprelyants; A.I Yaropolov (125-131).
Dynamics of transformation of Mycobacterium smegmatis cells by cultivation under nonoptimal conditions (partial starvation) to dormant, nonculturable form has been studied. For this aim, an electrochemical method was developed to detect both viable and ‘viable but nonculturable’ (VBNC) cells. The current produced by bacteria placed at the electrode surface was measured in the presence of 2,6-dichlorophenol indophenol (DCIP) at the applied potential of 350 mV. It has been established that electrochemical activity changes parallel with the growth of biomass. The transition of M. smegmatis to a dormant, nonculturable state goes along with the decrease of the detection current up to 20% of the maximum level. This means that nonculturable cells have rather high rest metabolic activity. The course of the CFU values has a complicated character during bacterial growth. The placement of the bacterial culture on the solid medium appears to cause a new stress that stops proliferation and stimulates aggregation. Both processes distort CFU measurement results. The quantitative estimation of the viable but nonculturable cells by counting colonies, measuring optical density and current produced by bacteria has been discussed.
Keywords: Bioelectrochemistry; Electrochemical approach; Dynamics of bacterial transformation; Nonculturable and dormant bacteria; Mycobacterium smegmatis; Partial starvation stress; Metabolism level; Computer processing; Revealing latent pathogens;

The present study aims to investigate the quercetin–deoxyribonucleic acid (DNA) interaction occurring in bulk solution either electrochemically using differential pulse voltammetry or spectrophotometrically, in order to explain the possible DNA-damaging activity of quercetin. A very weak interaction between quercetin and DNA in solution was found to take place. However, since extensive quercetin-induced DNA damage via reaction with Cu(II) has been reported, an electrochemical study of the DNA–Cu(II)–quercetin system in solution was undertaken. The product of DNA interaction with quercetin–Cu(II) complex was observed. Damages to DNA were electrochemically recognized via the increasing of the anodic peaks corresponding to the oxidation of guanosine and adenosine bases and spectrophotometrically via increasing of the 260 nm adsorption band. It was also observed that dsDNA damage produced by the quercetin–Cu(II) complex occurred with time. Control experiments with different mixtures of Cu(II), quercetin, ssDNA, dsDNA or poly[A] were carried out in order to establish a possible mechanism of interaction between DNA and quercetin via Cu(II).
Keywords: DNA-electrochemical biosensors; Quercetin; Oxidation; Electrochemistry; Radical scavenging activity; Flavonoids;

Electrochemical study of quercetin–DNA interactions by Ana Maria Oliveira-Brett; Victor C Diculescu (143-150).
Quercetin interaction with dsDNA was investigated electrochemically using two types of DNA biosensor in order to evaluate the occurrence of DNA damage caused by oxidized quercetin. The results showed that quercetin binds to dsDNA where it can undergo oxidation. The radicals formed during quercetin oxidation cause breaks of the hydrogen bonds in the dsDNA finally giving rise to 8-oxoguanine since the DNA guanosine and adenosine nucleotides in contact with the electrode surface can easily be oxidized. A mechanism for oxidized quercetin-induced damage to dsDNA immobilized onto a glassy carbon electrode surface is proposed and the formation of 8-oxoguanine is explained. The importance of DNA-electrochemical biosensors in the determination of the interaction mechanism between DNA and quercetin is clearly demonstrated.
Keywords: DNA-electrochemical biosensors; Quercetin; Oxidation; Electrochemistry; Radical scavenging activity; Flavonoids;

Static and 50 Hz magnetic fields of 0.35 and 2.45 mT have no effect on the growth of Saccharomyces cerevisiae by M.J Ruiz-Gómez; M.I Prieto-Barcia; E Ristori-Bogajo; M Martı́nez-Morillo (151-155).
The present work reports the growth effects induced by static and sinusoidal 50 Hz magnetic fields (MF) on the haploid yeast strain Saccharomyces cerevisiae WS8105-1C. Magnetic fields were generated by a pair of Helmholtz coils (40 cm in diameter) with 154 turns of copper wire in each and separated 20 cm. The experiments were performed at 0.35 and 2.45 mT, and yeasts were exposed to MF during 24 and 72 h in the homogeneous field area. Growth was monitored by measuring the optical density at 600 nm. The data presented in the current report indicate that static and sinusoidal 50 Hz MF (0.35 and 2.45 mT) do not induce alterations in the growth of S. cerevisiae.
Keywords: Magnetic field; Yeast; Saccharomyces cerevisiae; Growth; Proliferation; Mutant;

Cyclic voltammetry was successfully applied to study the oxidation of nicotinamide adenine dinucleotide (NADH) both in homogeneous and heterogeneous phase. The first case was realized with a solution containing p-methylamino-phenolsulphate (MAP) as redox mediator and the diaphorase (DI) from Clostridium kluveri as enzyme while the second one by using both a glassy carbon (GC) and a carbon nanotube paste (CNTP) electrode modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde (3,4-DHB). Such systems were successively coupled with glucose dehydrogenase (GDH) reaction to realize the redox chain present in glucose biosensors. A critical comparison of the two systems was also reported.
Keywords: NADH oxidation; Cyclic voltammetry; p-methylamino-phenolsulphate; 3,4-Dihydroxybenzaldehyde; Modified electrode; Carbon nanotube paste electrode;