In addition to the isolation and cultivation of pure strains, adequate preservation is also necessary. A wide variety of techniques are available for bacteria preservation. The primary aim of culture preservation is to maintain the organism alive, uncontaminated, and without variation or mutation, that is, to preserve the culture in a condition that is as close as possible to the original isolate.
Figure 1 Microbial Strains Preservation
Several methods have been successfully used for the preservation of microorganisms: repeated sub-culturing, preservation on agar beads, oil overlay of slant-grown cultures, use of silica gel and other sterile supports, cryopreservation and lyophilization. Among these, cryopreservation and lyophilization are highly utilized for culture collections and industry.
Cryopreservation refers to the preservation of biological materials at cryogenic temperatures, generally −80 °C, (dry ice) or −196 °C, (liquid nitrogen). Low temperature protects proteins and DNA from denaturation and damage and slows the movement of cellular water. Consequently, biochemical and physiological activities of the cells are essentially halted and cells are protected for long periods of time.
Lyophilization is the preferred long-term preservation method in most microbial resource centers (MRCs), due to the low cost of maintenance and ease of transportation of lyophilized cultures. Lyophilization gives satisfactory results for the preservation of many bacteria, yeast and sporulating fungi, but does not adequately preserve non-sporulating fungi, some species of yeast, and certain bacteria.
All microbiology laboratories preserve micro-organisms on agar slant. This is a simple and most economical method of preserving bacteria and fungi. Pure cultures can be successfully stored at 0-4°C either in refrigerators or in cold-rooms. This method is applied for short duration (2-3 weeks for bacteria and 3-4 months for fungi).
In this method, sterile liquid paraffin in poured over the slant (slope) of culture and stored upright at room temperature. The layer of paraffin ensures anaerobic conditions and prevents dehydration of the medium. This condition helps microorganisms or pure culture to remain in a dormant state and, therefore, the culture is preserved for several years. It is a simple and most economical method of maintaining pure cultures of bacteria and fungi.
Sodium chloride in high concentration is frequently an inhibitor of bacterial growth. Bacteria are suspended in 1% salt solution (sublethal concentration in screw cap tubes to prevent evaporation). The tubes are stored at room temperature. Whenever needed the transfer is made on agar slant.
Due to the vast diversity of microbial life and the time-consuming nature of preservation research, preserving medically, ecologically and industrially important strains would be paramount. We have established a mature technical platform to culture and preserve various microorganisms that can be isolated from readily available sources. Our microbiologists are dedicated to developing and optimizing robust preservation methods to ensure the long-term viability of different microorganisms. If you are interested in our microbial strains preservation service, please contact us for more details.