CHAPTER V 

 Maintenance and Preservation of Cultures 



Freeman A. Weiss 



INTRODUCTORY 



The title of this chapter suggests that there are two somewhat distinct 

 aims in keeping cultures of microorganisms — maintenance and preserva- 

 tion, or perhaps conservation would be a better term. Sometimes the 

 preservation of cultures is only a continuation of the process of maintain- 

 ing them, but often it implies something more. Maintenance means 

 essentially supporting the culture and keeping it alive, pure, and in 

 recognizably typical growth. Preservation has the connotation of long- 

 term maintenance, but in addition, in view of the propensity of all 

 organisms to vary — especially microorganisms because of the high fre- 

 quency of generations of which they are capable — it also means main- 

 taining them at essentially constant biological potentials. A preserved 

 culture, for example one lyophilized (from lyo, loose, + philos, loving) or 

 in dry soil, may appear macroscopically anything but typical, but it can 

 be restored to its typical morphology and usually to its initial physio- 

 logical and biochemical characteristics by suitable manipulation. On 

 the other hand, cultures that are merely maintained may show typical 

 form, may grow luxuriantly, but if they have lost some biological charac- 

 teristic for which they were primarily selected, they have not been satis- 

 factorily preserved. 



The basic function of a culture collection is to conserve cultures, not 

 merely maintain them. This distinction does not always appear, but it 

 exists, and it is with this in view that the methods and materials recom- 

 mended in this chapter were selected. They are essentially the pro- 

 cedures adopted by the American Type Culture Collection after long 

 experience in both maintaining and preserving cultures. These methods 

 also are subject to constant change as better techniques or materials are 

 discovered, and no claim to universal application or general superiority 

 is or can be made. In fact the procedures outlined here should always be 

 supplemented, at least for routine maintenance of cultures, by technics 



99 



