MICRO-ORGANISMS 27 



contamination as long as the tube is unopened. Second, lyophilized 

 cultures are essentially dormant and therefore changes associated with 

 growth are absent. Strains removed from lyophil have the same 

 physiological, cultural, and morphological characteristics as before 

 lyophilization. The value of retaining these characteristics is obvious 

 in industrial fermentations and in taxonomical investigations. Third, 

 the longevity of lyophilized cultures exceeds that of cultures main- 

 tained by any other method. For example, Lactobacillus leichmannii, 

 which often fails to survive more than a week in refrigerated stab or 

 deep cultures, has been recovered repeatedly from lyophil after as long 

 as 3i/2 years. Probably it would survive for at least 5 to 10 years. 



Our experience with lyophilization has entailed the processing of 

 more than 10,000 strains in about 60 genera of bacteria, all available 

 species of actinomycetes, and most yeasts and other fungi, especially 

 in the genera Aspergillus and Penicillium and in the order Mucorales. 

 The ARS Culture Collection of micro-organisms has been maintained 

 for about 20 years. Among the bacteria, yeasts, and molds in this 

 collection, no large or important group has failed to survive lyophili- 

 zation. 



Contrary to general opinion, lyophilization does not require expen- 

 sive equipment, lengthy processing, or highly trained technicians. 

 The most expensive piece of equipment needed is a vacuum pump, like 

 that found in most microbiological laboratories. The remainder of 

 the apparatus consists of a manifold and a cold trap, which can be 

 made by a glassblower, and assorted pieces of glass and rubber tubing. 

 The manifold is generally made to hold two to three dozen tubes, so 

 that many tubes of one culture or one or a few tubes of several cultures 

 may be processed simultaneously. 



By the methods used successfully at the ARS Culture Collection, 

 30 tubes may be completely processed in 2 hours. During this period 

 the cells or spores are scraped from slants or plates or centrif uged out 

 of broth culture, suspended in bovine serum, dispensed to lyophil 

 tubes, frozen, dried, and sealed with an oxygen-gas crossfire torch. 

 The resulting lyophilized cultures are stored in vials in a refrigerator. 

 An ordinary 9-cubic foot household refrigerator fitted with trays holds 

 about 20,000 lyophil tubes. In a similar space the number of test-tube 

 cultures that could be accommodated would not exceed 2,500. Cul- 

 tures lyophilized by this method are viable for years. Those put up 

 in 1940,^ when the ARS Culture Collection was established, are viable 

 and typical after more than 20 years. 



Lyophilization of cultures for industrial fermentations is especially 

 useful. When a run is unusually successful, it is a good practice to 

 reisolate the fermentative agent and to make multiple lyophil cultures 

 for future reference. Thereafter, whenever the current culture is 

 suspected of becoming unsatisfactory for any reason, it is best to dis- 

 card it and to begin succeeding runs with a culture freshly removed 

 from lyophil. Such procedures will save much time and tedious work. 



NOMENCLATURE AND TAXONOMY 



Nomenclature and taxonomy, two subdivisions of the sciences, are 

 of special concern and applicability to the biological scientist. No- 



