Some observations in freeze-drying of recombinant bioluminescent Escherichia coli for toxicity monitoring

A recombinant bioluminescent bacteria, containing a fabA::luxCDABE fusion g ene, has been used to characterize freeze-drying methods, which may be conv eniently used as a tool for the development of a portable biosensor. Throug h residual water, viability, biosensing activity and scanning electron micr oscopy analyses, the characteristics that four cryoprotectants, trehalose, sucrose, sorbitol, and mannitol, conferred on freeze-dried samples were elu cidated, including the morphology, water content and activity of the cells. It was found that trehalose showed the best freeze-drying efficiency among the tested cryoprotectants and it might have a specific capacity limitatio n in protection of the cells during the freeze step. Humidity might result in damage to the cells, according to the viability, when exposed to air dur ing storage, while the water remaining post freeze-drying showed good corre lation with damage to the freeze-dried cells when under air-tight storage c onditions. The results with other recombinant bioluminescent bacteria indic ated that these findings might be general features of the freeze-drying pro cesses. (C) 2001 Elsevier Science B.V. All rights reserved.