Chapter 9 : Procedures for the Storage of Microorganisms *

Abstract:

This chapter presents methods that can be used for the storage of bacteria, protozoa, fungi, and viruses. There are two types of cryoprotective agents: those that enter the cell and protect the intracellular environment and others that protect the external milieu of the organism. Glycerol and dimethyl sulfoxide (DMSO) are most often used for the former; sucrose, lactose, glucose, mannitol, sorbitol, dextran, polyvinylpyrrolidone, polyglycol, and skim milk are used for the latter. To protect microorganisms from damage during the freezing process, during storage, and during thawing, cryoprotective agents are often added to the culture suspension. Whereas most bacteria, fungi, and viruses survive better with such additives, studies have shown that cryoprotective agents significantly damage others. Freeze-drying is considered to be the most effective way to provide long-term storage of most bacteria, yeasts, sporulating molds, and viruses. The preparation is then used in smaller volumes as described above for freezing. All of the material presented in this chapter applies primarily to the preservation of bacteria. Subculturing is the simplest method of maintaining living fungi and involves serial transfer to fresh solid or liquid media. Storage is accomplished usually at room or refrigerator temperature. All of the techniques described have been applied to the storage of yeasts and fungi. Viruses tend to be more stable than other microorganisms because of their small size and simple structure, and the absence of free water. Many viruses can be stored for months at refrigerator temperatures or for years by ultralow-temperature freezing or freeze-drying.