PRESERVATION OF CULTURES 53 



Preservation in Lyophile Form 



Studies now in progress at the Northern Regional Research Laboratory 

 indicate that many, if not all, of the Aspergilli can be successfully main- 

 tained in a dried state for extended periods. Viability tests for a number of 

 species including A. terreus, A. niger, A. oryzae, A. flavus, and A. itaconicus 

 have been made at 3£ years; while a much greater and wider variety of 

 forms has been tested at 20 to 24 months. Positive results have been ob- 

 tained with all cultures tested, although comparatively few colonies devel- 

 oped from certain strains of A. niger, A. flavus, and the large-spored 

 members of the A. glaucus group. Observations are being continued and 

 in time information will be obtained as to the feasibility of employing this 

 as the principal means of maintaining a collection of molds. It is known 

 that many bacteria, especially staphylococci, streptococci, and pneumo- 

 cocci can be successfully preserved for periods up to 16 to 18 years (Elser, 

 Thomas, and Steffen, 1935; Swift, 1937). Wickerham and Andreasen 

 (1942) have presented evidence covering a period of one year which suggests 

 the practicability of applying the method to the yeasts. Such information 

 as we have to date regarding the molds seems to indicate that the method 

 may prove of great significance in two ways: first, as a means of prolonging 

 viability, and second, as a means of preserving in viable form spores of a 

 particular "generation," or other selected origin, which can be used in 

 comparative tests over a period of many months or even years. 



The drying technique employed at the Northern Regional Research Lab- 

 oratory is essentially like that described by Wickerham and Andreasen 

 (1942) and may be briefly summarized as follows: 



Employing aseptic techniques throughout, the spores from selected 

 cultures are suspended in sterile beef, or horse serum. The resulting sus- 

 pension is then dispensed into small cotton-stoppered Pyrex glass tubes 

 6 mm. by 100 mm. that have been properly labeled with glass-marking ink. 

 Approximately 0.05 to 0.1 cc. of the spore suspension is added to each tube 

 by means of a long thin-necked pipette. Most of the cotton plug is burned 

 away, and the remaining portion pushed down into the tube to prevent 

 possible contamination during the drying process. The tubes are inserted 

 in rubber sleeves on the manifold, as shown in figures 14 A and B, and low- 

 ered into a freezing bath of carbon dioxide ice and methyl cellosolve at a 

 temperature of approximately —40° C. The suspension is frozen almost 

 instantaneously. The manifold is connected to a vacuum pump and evacu- 

 ation and desiccation initiated. Water is removed from the system by the 

 insertion of a water-trap immersed in a C0 2 -methyl cellosolve filled Dewar 

 flask as shown in figure 14A, or in a column of drierite (anhydrous CaS0 4 ) 

 as shown in figure 14B. After a few minutes the temperature of the bath 



