Determination of the electrokinetic potential of Rhizobium leguminosarum bv trifolii Rt24.2 using Laser Doppler Velocimetry--a methodological study.

Electrokinetic potential (ζ, zeta potential) is one of the parameters which characterize the physicochemical properties of the bacterial cell envelope. The term is often used in the context of adhesiveness of bacteria and biofilm formation. This work presents the methodological aspects of zeta potential determination in strain Rt24.2 of Rhizobium leguminosarum using Laser Doppler Velocimetry combined with Phase Analysis Light Scattering and changed electric field techniques. The influence of media (0.9% NaCl, 0.2% NaCl, TY, GYM, 79CA, 20E and M1), temperature of measurement, number of measurement repetitions, phase of culture, concentration of bacteria, and storage at low temperature on the value of electrokinetic potential was investigated and a comparison was drawn between live and dead bacteria. All of those factors modified the zeta potential, showing that these parameters should be precisely specified in studies of bacterial electrokinetic potential, which is not always done. The obtained results also indicated that the zeta potential of Rhizobium leguminosarum should be determined directly in samples without storage at a defined bacterial density. The measurement should be done only once in a sample inserted into the cell of a measuring device to eliminate changes occurring in the sample (increase of electrolytic conductivity) under the electric field used.