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 20 kHz - 2 MHz, 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. (C) 2009 Elsevier Inc. All rights reserved.