Preservation and Maintenance

Factors should be taken into account when selecting the method of preservation (Parton and Willis, 1990) The degree of viability required on preservation The consequence of population and genetic changes on the organisms The number of samples requiring preservation The frequency of culture withdrawal The unit cost of the method chosen The nature of the culture The type of equipment available in the laboratory

Cryopreservation Freezing in liquid nitrogen or in freezers at -135 or below is the best preservation method for all cell type. The handling techniques, cryoprotectant (glycerol, dimethylsulfoxide, etc. ), freezing protocol, and thawing rates can be optimized for the particular cell. Provision must be made to safeguard against mechanical and electrical failure and the level of liquid nitrogen in the refrigerator must be maintained.

Freeze-drying (lyophilization) It is a more useful technique if the cells are to be distributed from the collection. Fewer organisms survive this technique and recovery of cells is lower than from cryopreservation. Freeze-drying should be optimized for different cell types. Most bacteria and most sporulating fungi are applicable. It is generally unsatisfactory for eukaryotic microalgae.

L-drying & oil storage Drying under vacuum without freezing (from the liquid state) has been used successfully for bacteria that are particularly sensitive to the initial freezing stage of freeze-drying. Storage on agar slant under a layer of paraffin has been used successfully for filamentous fungi as a long-term method. Bacteria are expected to survive 2-4 years.

Examples of some culture collections American Type Culture Collection (ATCC, atcc.org ), Manassa, Virginia, USA (All) Bioresource Collection and Research Center (BCRC, formerly CCRC, indexe.htm ), Food Industry Research and Development Institute, Hsinchu, Taiwan R.O.C. (All) Centraalbureau voor Schimmelcultures (CBS), Baarn, The Netherlands (Filamentous fungi and yeasts) Collection Nationale de Cultures de Microorganisms (CNCM), Paris, France (All) Deutsche Sammlung von Mikroorganismen und Zelkulture (DSMZ), Braunscheig, Germany (All) European Collection of Animal Cell Cultures (ECACC), Centre for Applied Microbiological Research (CAMR), Porton Down, UK (Animal cell cultures) National Collection of Industrial & Marine Bacteria (NCIMB), Aberdeen, UK (Bacteria)

ATCC CCRC Cryoprotectant Lyophilization