Electrically induced concentration fluctuations in Escherichia coli suspensions

Biological cells are permanently exposed to electric fields by self generated or external electrical sources. It is important to understand whether and how very weak electric fields influence the electric properties of biological cells. In the present study, we demonstrate by the electro-optic method the induced concentration fluctuations in suspensions of Escherichia coli cells subjected to alternating electric fields of low intensity (20-240 V cm(-1)) and low frequency (0.2-100 Hz). A frequency window is formed where concentration fluctuations are already significant, but the sample is still stable enough under the action of the field and permits the application of longer pulses. Our assumption is that, in this range, conditions are created for the accumulation of considerable induced local density variations and the latter could be responsible for the appearance of instability and electroporation of E. coli cells at similar conditions. (C) 2002 Elsevier Science B.V. All rights reserved.