Interaction of the fluorescent dye 1-N-phenylnaphthylamine with Escherichia coli cells during heat stress and recovery from heat stress.

The fluorescent dye 1-N-phenylnaphthylamine permeated Escherichia coli cells after exposure to a heat stress at 55 degrees C in Tris/Mg2+ buffer, pH 8.0. The rate of dye permeation increased with time during heat treatment and decreased gradually during subsequent incubation at 37 degrees C in a minimal medium. The initial level of rapid adsorption of the dye also increased with heating time, although it remained roughly constant during post-heating incubation. The results obtained suggest that the permeability barrier to the dye in the outer membrane was damaged by heat stress and was repaired after sublethal heating. RNA, protein and lipid syntheses, as well as an energy-yielding process, appeared to be necessary for the repair of impermeability to the dye.