Phage production and maintenance of stocks, including expected stock lifetimes

In microbiology, preservation of an archival stock or a "master stock" of a given microorganism is essential for many reasons including scientific research, conservation of the genetic resources and providing the foundation for several biotechnological processes. The objective is to preserve the initial characteristics of the microorganism and to avoid the genetic drift that occurs when the organism is maintained indefinitely in an actively growing state. The same holds true in phage biology and it is of particular interest when a collection of phages is to be maintained. The aim of this chapter is to provide phage biologists with general procedures to prepare and maintain bacteriophage stocks on a long-term basis. The protocols described below should be considered as general guidelines because although many phages and bacterial strains can be propagated and stored in these conditions, specific media and/or growth and storage conditions must be evaluated for each phage and bacterium. Since it was not the scope of this chapter to provide an exhaustive list of these particular conditions, we instead highlighted the main factors affecting phage amplification and storage. We hope this will help phage biologists to develop their own strategies for their preferred phages.