Long-term preservation of active luminous bacteria by lyophilization

A simple method for long-term preservation of luminous bacteria is described. Cells of Vibrio fischeri, Photobacterium leiognathi and four strains of P. phosphoreum were suspended in a protective medium of low ionic strength (1% NaCl) supplemented with 15% lactose and 2% soluble starch, and lyophilized. The freeze-dried preparations were sealed under vacuum and stored at 4 degrees C. Luminous bacteria were resuscitated after six months by adding 2% NaCl up to the original volume. The rehydrated cells exhibited 16-28% of initial bioluminescence so that they could be used for a microbial test of toxicity (the Microtox test). This method is also useful for maintaining luminous bacteria in strain collections.