Relationship between electroporation conditions, electropermeability and respiratory activity for Frankia strain ACN14a.

The use of electroporation for introducing macromolecules into intact cells of the actinomycete Frankia was investigated. Electropermeability was demonstrated by the uptake of dextran (70 kDa) molecules labeled with fluorescein isothiocyanate (FITC) inside Frankia cells. Upon pulsation with an exponentially decaying electric field, the cell membranes became permeable. Loading increased with initial pulsed electric field strength and capacitance. Increased loading efficiency was inversely related to INT (2-(p-iodophenyl-3-(p-nitrophenyl)-5- phenyltetrazolium chloride) reduction activity (respiring bacteria) of the cell population. The presence of CaCl2 in the electroporation and resealing buffer raised INT-reduction activity but K2SO4 decreased this activity. Resealing of electropores was confirmed by a decreasing FITC-dextran loading through the recovery period. The use of FITC-dextran molecules and INT-reduction assay are two new approaches for the study of permeabilization and cellular activity of electroporated bacteria.