Membrane malfunctions in freeze-dried Escherichia coli

Abstract

Freeze drying and exposure to oxygen of E. coli causes damage to the bacterial cytoplasmic membrane. Freeze-drying itself produces an injury to the transport system for ONPG and potassium, so as to make the membrane leaky to these compounds. This damage is partially repaired upon incubation of the reconstituted bacteria in nutrient medium. When, however, freeze dried bacteria are not held in vacuo before reconstitution, but exposed to oxygen, this damage to the bacterial membrane becomes more extensive and irreversible.