Influence of Cytoplasm Electrolyte Concentration on Maxwell−Wagner Polarizability of Bacteria E. coli

Abstract

The electric polarizability of bacteria is considered in the literature to have a surface charge dependent (ChD) and a Maxwell-Wagner (MW) mechanism. We distinguish experimentally both the types of interface polarizability by the frequency of the electric field and the medium electrolyte concentration. It was shown in a previous work ( Zhivkov , A. M. ; Gyurova , A. Y. Colloids Surf., B 2008 , 66 , 201. ) that the ChD component is shown up on the outer bacteria surface even at megahertz frequencies. The MW polarizability is studied in the present work in the range from 20 kHz to 20 MHz by change in the inner (cytoplasm) electrolyte concentration. The ion transport through the cytoplasmic membrane of alive and fixed by formaldehyde E. coli K12 is accelerated by adding of ethanol in low concentration. The frequency dependence and the kinetics of the electric polarizability and the size of the bacteria are investigated by conservative electric dichroism, based on the alteration of the optical density at orientation of the cells in electric field. The conclusion is that the internal MW component has the main contribution to the change in the total bacteria polarizability, as well as the external MW and the internal ChD components are not shown up.

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

“…It was shown that the ionic flow through the ethanol treated membrane is not able to change significantly the outer electrolyte concentration at our experimental conditions and therefore the magnitude of EChD component remains almost constant [14]. This means that the decrease in the difference between the values of polarizability in absence and in presence of 10 vol.% ethanol with the increase in the electrolyte concentration is not related to an additional decrease in EChD component except that resulting from the presence of KCl.…”

“…The estimation of the inner electrolyte concentration showed that it is high enough and therefore IChD component practically does not exhibit. That let us to conclude that IMW component has the main contribution on the inner membrane surface at the frequency range mentioned above [14].…”

“…Furthermore, it has been shown that the increase in the ionic strength after incubation in 0.1 M KCl results in polarizability increase. We note that in the mentioned experiment the bacteria were firstly incubated in distilled water (which leads to a slow decreasing of the cytoplasm electrolyte concentration, which usual value is about 0.1 M [14]) and then in 0.15 M KCl, which causes cytoplasm concentration increasing (faster at the ethanol presence). The estimation of the inner electrolyte concentration showed that it is high enough and therefore IChD component practically does not exhibit.…”

“…The existence of two charged surfaces of bacteria cover leads to consider two ChD components-external (EChD) and internal (IChD). So, we take into account four components of the electric polarizability [12][13][14] like it was suggested for erythrocytes [5]. The considering of only two polarizability components is correct in the case of solid particles, but it has been applied for bacteria by now too [6,7,11].…”

“…In our articles regarding bacteria electric polarizability we have suggested an experimental way for distinguishing the types of surface polarizability by changing the outer and inner electrolyte concentration and with the frequency of the applied electric field [12][13][14]. Our approach is based on a principle difference between ChD and MW polarizability components-they have completely opposite behavior by varying the ionic strength: ChD polarizability decreases [6,7,11] and MW one increases [1,10] with the increase in the electrolyte concentration.…”