ARS OPEN COLLECTION STRAIN ACCESSION POLICIES

Microorganisms may be accepted into the open or public portion of the ARS Culture Collection at the discretion of the appropriate curator. Strains accepted for deposit should not be particularly fastidious in their growth requirements and must not exceed biosafety level 2 classification (i.e., strains must not be highly communicable and cause serious illness or death). Plant, human, and animal cell lines are not accepted. Detailed inquiries should be directed to the appropriate curator. A copy of the deposit form in PDF format can be obtained by clicking here.

The ADOBE® Acrobat® Reader® software needed to view and print this form can be downloaded at no charge by clicking here:

STRAIN MAINTENANCE IN THE COLLECTION

The majority of strains maintained in the ARS Culture Collection are kept as lyophilized (freeze-dried) preparations. Culture ampules in refrigerated storage are seen in the photo to the left.

The first large-scale use of lyophilization for culture preservation was pioneered at NCAUR by Wickerham for yeasts and by Raper for aspergilli and penicillia. The process consists of freezing microorganisms within small glass ampules in an appropriate liquid suspending medium such as bovine serum and applying a vacuum to sublime the water from the frozen preparations. Following drying, the ampules are sealed under vacuum with a gas-oxygen torch and then stored at 5ºC.

Lyophilized cultures are revived by breaking the ampule and placing the pellet of cells in a small tube of broth. Depending on the microorganism, the resuspended pellet may be incubated in a liquid medium or streaked onto agar. Viability of most organisms following lyophilization is seldom more than a few percent, giving rise to the concern that the process may select for atypical cells in the population. While there is some evidence to support this contention, the majority of strains appear genetically unchanged by the procedure and are certainly more faithfully preserved than by serial transfer on agar slants. Viability of lyophilized cultures can usually be measured in decades.

Some microorganisms, such as asporogenous filamentous fungi and certain yeasts and bacteria, do not survive the lyophilization process. These strains are maintained as frozen stocks in liquid nitrogen. Liquid nitrogen storage seems to cause little or no genetic change in cells. The reasons for not relying on this method exclusively for preservation of cultures are: cost and the fact that lyophilized preparations may be shipped by regular mail whereas strains preserved by liquid nitrogen must first be grown on agar or in liquid medium to avoid the expense of shipping frozen materials.