Influence of cytoplasm electrolyte concentration on Maxwell-Wagner polarizability of bacteria E. coli

Dielectrophoretic analysis of the impact of isopropyl alcohol on the electric polarisability of Escherichia coli whole-cells

Whole-cell biocatalysts are versatile tools in (industrial) production processes; though, the effects that impact the efficiency are not fully understood yet. One main factor that affects whole-cell biocatalysts is the surrounding medium, which often consists of organic solvents due to low solubility of substrates in aqueous solutions. It is expected that organic solvents change the biophysical and biochemical properties of the whole-cell biocatalysts, e.g. by permeabilising the cell membrane, and thus analysis of these effects is of high importance. In this work, we present an analysis method to study the impact of organic solvents on whole-cell biocatalysts by means of dielectrophoresis. For instance, we evaluate the changes of the characteristic dielectrophoretic trapping ratio induced by incubation of Escherichia coli, serving as a model system, in an aqueous medium containing isopropyl alcohol. Therefore, we could evaluate the impact on the electric polarisability of the cells. For this purpose, a special microchannel device was designed and Escherichia coli cells were genetically modified to reliably synthesise a green fluorescent protein. We could demonstrate that our method was capable of revealing different responses to small changes in isopropyl alcohol concentration and incubation duration. Complementary spectrophotometric UV-Vis (ultraviolet-visible light) absorbance analysis of released NAD(P)+/NAD(P)H cofactor and proteins confirmed our results. Based on our results, we discuss the biophysical effects taking place during incubation. Graphical abstract.

Electro-optic properties of organic nanotubes

In this review article the theoretical and experimental possibilities of applying EO-methods for estimation of the physico-chemical properties of the organic nanotubes (ONTs) are studied. The ONTs are highly organized nanostructures of strongly elongated, anysometric, and hollow cylinders with a size range of 1 nm to 10,000 nm, e.g. in aqueous solutions they could behave as colloid (disperse) particles. They have high interaction ability due to their extremely large curved, rolled-up external surfaces (bilayers of membrane walls) and unique properties because of their specific electric charge distribution and dynamics that make possible the functionalization of their surfaces. Thus they could template guestsubstances such as membrane proteins and protein complexes on the exterior surfaces and in the membrane. We performed our investigations for the case of ONT aqueous colloid suspension. Following our earlier proposition of the general expression for the electro-optic (EO) effect we derived equations for the evaluation of the electric properties of ONT particles such as mechanism of electric polarization and identification of their most important electric Dipole Moments (DM), permanent (pDM) and induced (iDMs). Further we recommend ways for the calculation of their magnitude and direction. Also we evaluated some geometrical properties such as length of the ONT particles and their polydispersity. The knowledge that we provided about the ONT properties may enable us to elucidate and predict their biological activity. Templating biological active ligands (such as membrane proteins and protein complexes) on the inner and outer surfaces as well as in the surface membrane creates their potential usefulness as carrier and deliverer of biopharmaceuticals in bio-nanodevices. The theoretical equations were compared with the experimental data for ONTs such as (lipid) LNT, Tobacco Mosaic Virus (TMV) and microtubules (MT). Comparison of EO methods with other methods used till now shows that the EO methods are faster, not invasive and do not alter the studied particles.

Polymer concentration dependence of kilohertz electric polarizability of alumina colloid particles with adsorbed carboxymethyl cellulose

Polyelectrolytes are soluble polymers composed of units having charged groups. Because of the high charge density, some of the counterions are adsorbed electrostatically (ion condensation) on the polyelectrolyte chain. It was shown that in direct electric field the condensed counterions and the chain move together as one whole but it is assumed that they are mobile in alternating field and participate in the polarization. Experimental evidence is obtained by electro-optical investigations of polyelectrolytes adsorbed on colloid particles-the observed low-frequency shift of the polarizability relaxation has been interpreted as condensed counterions' mobility. The present investigation aims to verify the reports for the condensed counterions' mobility in sinusoidal electric field. By means of electric light scattering we investigated a water suspension of γ-alumina particles with adsorbed carboxymethyl cellulose. Instead of the previously used frequency approach (dispersion dependence at saturated adsorption of the polyelectrolyte) we applied an amplitude approach-determination of the polarizability at frequency 1 kHz and increasing polyelectrolyte concentration (from zero to full adsorption saturation). The results indicate the absence of polarization owing to the condensed counterions. The main evidence was obtained by comparison of the concentration dependences of the polarizability (depending on all mobile counterions) and the electrophoretic mobility (determined only by the diffuse counterions). We concluded that the condensed counterions are immobile in sinusoidal field with intensity up to 0.5  kV cm (- 1) and frequency of 1 kHz and higher.

Electric polarizability changes during E. coli culture growth

The electric polarizability of bacteria has two main components: surface-charge dependent (SChD) and Maxwell-Wagner (MW). It has been reported that the low frequency SChD component of Escherichia coli K12 still arise in the frequency range 20kHz - 2MHz, together with the high-frequency MW one. All the previous experiments were carried out with bacterial cultures of E. coli K12 in the stationary phase. In the present work we study electric polarizability during culture growth with the aim of finding out how it is influenced by the physiological state of the cells. The electro-optical method of electric turbidimetry is used, which is based on the change in the optical density as a result of orientation of bacterial cells under the action of an applied electric field. Our results show that until the cell concentration increases exponentially, the polarizability and the cell size change synchronously, so that the polarizability is approximately a quadratic function of the average bacterial length. We explain this with dominance of the SChD component. However, that after the polarizability deceases twofold at insignificant length oscillations and the power of the function decreases to 1.5. The last result is interpreted as an increase in the MW component.

Influence of the medium electrolyte concentration on the electric polarizability of bacteria Escherichia coli in presence of ethanol

The electric polarizability is an important parameter of bacteria, giving information about the electric properties of the cells. In our previous works [A.M. Zhivkov, A.Y. Gyurova, Colloids Surf. B: Biointerfaces 66 (2008) 201; A.Y. Gyurova, A.M. Zhivkov, Biophys. Chem., 139 (2009) 8; A.M. Zhivkov, A.Y. Gyurova, J. Phys. Chem. B, 113 (2009) 8375] we have applied an experimental approach to distinguish the contribution of the components of the two types of interface electric polarizability-surface charge dependent (ChD) and Maxwell-Wagner (MW) polarizability. It is based on electro-optical study of the separate influence of the outer and inner medium electrolyte concentration, which changes the external ChD and internal MW components of polarizability; the last effect is reached by the membrane permeability increase in low ethanol concentration. In the present work we investigate the behavior of electric polarizability of Escherichia coli K12 at increasing the outer KCl concentration in presence of 10 vol.% ethanol in order to check if the polarizability components change independently from one another. The conclusion is that the outer electrolyte concentration influence indirectly the internal MW component by the trans-membrane concentration gradient, but the polarizability components themselves change independently.