The conservation of microbes is similar to that of animal and plant conservation. Microbes, like animals and plants do not get extinct or endangered but they lose important traits with time either by spontaneous mutations or loss of certain genes. Microbial traits have been exploited for numerous, industrial, environmental, ecological, agricultural, medical and biotechnological purposes. It is hard to find any branch of science or engineering which is devoid of microbial application. So for future applications and study, they deserve to be conserved and that too scientifically. While plants and animal are conserved and protected in sanctuaries or parks, microbes are conserved in laboratories and collection centers/banks using specialized techniques.
Microbial conservation centers: Approximately, every country in the world have one or more microbial culture collection centers. Some microbial collection and conservation centers in the world are enlisted;
- American Type Culture Collection (ATCC), USA
- Bioresources Collection and Research Center (BCRC), Taiwan
- Collection of Aquatic Important Microorganisms (CAIM), Mexico
- Culture Collection of Algae and Protozoa (CCAP), UK
- Marine Biotechnology Institute Culture Collection (MBIC), Japan
- Microbial Type Culture Collection and Gene Bank (MTCC), India
- National Bank for Industrial Microorganisms and Cell Cultures (NBIMCC), Bulgaria
- National Collections of Industrial, Food and Marine Bacteria (NCIMB), UK
- National Collection of Yeast Cultures (NCYC), UK
- Agricultural Research Service Culture Collection (NRRL), USA
Laws of microbial conservation: The basic functions of existing culture collection centers in isolation, identification, maintenance; promotion and development of new collection banks or encouragement for new initiatives of collecting cultures and provision of standard scientific services are governed by WFCC (World Federation of Culture Collections) of IUMS (International Union of Microbiological Societies) and IUBS (International Union of Biological Sciences) commission. They recommend good culture collection practices; provide guidance in the form of guidelines to maintain authenticity of each culture and also to maintain microbiologically high standards of operation of all types of culture collection centers in the world.
The conservation methods
There are lot of methods of culture preservation which have been modified by individual culture collection centers for feasibility and using available resources. Basic conservation methods of bacteria are:
Subculturing or subcultivation: it is the oldest method of microbial preservation and is routinely performed in all microbiological laboratories. It involves transfer of colony mass from agar medium to suitable growth medium. They are maintained as agar slant cultures in a refrigerator. The cultures are periodically transferred to fresh media to retain viability.
Saline suspensions: Saline is inhibitory to bacterial growth. Therefore bacterial growth is inoculated in 1% saline. The suspension in screw caps can be stored at room temperature.
Agar slant cultures covered with oil: In this method, good bacterial growth on agar slants is covered with sterile mineral oil (1cm above tip of slant). Cultures can be transferred from slants whenever needed.
Preservation by vacuum drying: Microbes are dried in vacuum and stored in refrigerator for long time.
Preservation at very low temperature: Microbial growth is suspended in nutrient broth containing 15% glycerol or skim milk with 7.5% glucose. The suspension is frozen and preserved at -15 to -30˚C or in liquid nitrogen refrigerator.
Freeze drying or Lyophilization: This is most efficient and reliable method for storing cultures as long as 10years. In this method, microbes in ampoules are frozen over inside surface of vial by rotating in mixture of dry ice and alcohol at -78˚C. Frozen cells are immediately dried in vacuum. Lyophilization is also used for storage of sera, toxins, toxoids and enzymes.
Conservation of fungi, Actinomycetes and yeasts; algae, plant and animal viruses: Fungi are preserved as spores or spores and hyphal stage together in liquid nitrogen, lyophilization, and sterile soil or in sterile distilled water. Yeasts are stored by methods employed for bacteria. Algae are preserved by cryopreservation using suitable preservative in liquid nitrogen. Viruses are stored in liquid nitrogen at -196˚C in liquid phase or -150˚C in vapor phase.
Conservation of genome/gene sequences: It is stored as sequence database consisting of protein and nucleotide sequences of DNA from different microbes.
In all types of conservation methods, the microbes are stabilized into anabiotic state; meaning reduced or completely stopped vital metabolic activities of a cell. The microbial cell cannot be called dead as it is able to revive normal functioning when conditions are suitable. Thus anabiotic state is microbial adaptation to survive under imposed conditions of preservation. The growth media should be such that it should not alter biochemical or morphological characteristics of organism during storage and also support nutrient requirements of microbe during long storage.
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