Which of the following is preferable method for the long term storage of Microoraganisms?
Microbial resource centers and preservation research … Lyophilization is the preferred long-term preservation method in most MRCs due to the …
Lyophilization is the preferred long-term preservation method in most 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 (vegetative hyphae), some species of yeast (Lipomyces, Leucosporidium, Brettanomyces, Dekkera, Bulleera, Sporobolomyces) and certain bacteria [Aquaspirillum serpens, Clostridium botulinum, Helicobacter pylori; Smith et al., 2008)]. Lyophilization exerts stress on the cells during vacuum desiccation, and cells raised under stress may respond better to lyophilization (Morgan et al., 2006; Smith et al., 2008). For instance, a culture at stationary phase and low pH condition survived better during lyophilization than did cells in log phase grown at circumneutral pH (Palmfeldt & Hahn-Hagerdal, 2000; Corcoran et al., 2004). However, the above-mentioned generalization is not true for all groups of bacteria (Boumahdi et al., 1999). In general, a suspension medium with 1 × 108 cell mL−1 or more gives a better recovery, whereas glass-forming cryoprotectants are preferred over a eutectic crystallization salt (palmfeldt et al., 2003; Morgan et al., 2006). Although techniques of lyophilization are well established, optimization of lyoprotectants and suspension media are still necessary for certain microorganisms (Crowe et al., 1998; Miyamoto-Shinohara et al., 2000; Carvalho et al., 2003; Gomez Zavaglia et al., 2003; Streeter, 2003; Berner & Viernstein, 2006; Tindall, 2007; Siaterlis et al., 2009). An ideal suspension medium for lyophilization should contain lyoprotectants and matrix materials or excipients. The use of stationary phase cultures, borosilicate ampules, a 1–2% final moisture content of the lyophilized specimen, and storage at 4 °C in the dark are recommended for higher cell viability and longer stability with lyophilization (Morgan et al., 2006; Smith et al., 2008).
Both cryopreservation and lyophilization have advantages and disadvantages, and the response of preservation varies by species. Even different strains of the same species may respond differently to the same preservation method. The viability and longevity of microorganisms under preservation depends on some critical factors: (1) composition of the suspension and rehydration medium, (2) type of cryoprotectant used, (3) rate of cooling and thawing, (4) growth stage of the culture, (5) cell size and type, lipid content, water content, and initial density of cells (De Kievit et al., 2001; Hubalek, 2003; Ren et al., 2004; Morgan et al., 2006; Smith et al., 2008; Chian, 2010) Reff