Protection of freeze-dried Escherichia coli by trehalose upon exposure to environmental conditions.

Freeze-dried cultures of wild-type and genetically engineered strains of Escherichia coli lost their colony-forming ability upon exposure to air, visible light, and certain relative humidity levels. Both strains could be maximally protected from these lethal effects with 100 mM trehalose, a concentration calculated to just saturate the interphospholipid spaces in the cell membrane, thus preserving the liquid-crystalline structure. The trehalose protection was observed for at least 96 h. Trehalose increased viability as much as 2000-4000% over nontreated populations. In all cases, exposure to environmental conditions was more damaging to the genetically engineered strain.