This study investigated how different Escherichia coli strains survive storage at -18°C in glycerol-containing media. Researchers tested 22 bacterial strains with varying DNA repair capacities, including wild-type and mutants deficient in genes like polA, uvrA, uvrB, uvrC, uvrD, recA, recF, lexA, and lon. Cultures were grown in LB medium, suspended in either LB medium or buffered saline (both with 50% glycerol), and stored at -18°C. Survival was measured by colony-forming ability over time. Results showed marked differences in cold-storage sensitivity among strains, but surprisingly, this sensitivity was not correlated with DNA repair capacity. Genetic control of storage death was evident from consistent strain differences, though some variability occurred between experiments. Growth temperature (30°C vs 37°C) did not affect survival. The suspending medium composition influenced survival, with buffered saline providing better protection than broth. The authors concluded that cold-storage lesions cannot be repaired by known repair mechanisms and that reproducible cold storage requires precise experimental control, particularly careful cooling procedures.

Key findings

• Storage death at -18°C in E. coli is genetically controlled but independent of known DNA repair mechanisms (polA, uvrA, uvrB, uvrC, uvrD, recA, recF, lexA, lon genes)
• Different bacterial strains showed markedly different sensitivities to storage death, with some strains maintaining colony-forming ability better than others
• Suspending medium composition significantly affected survival, with buffered saline providing better protection than LB broth medium
• Growth temperature prior to storage (30°C vs 37°C) did not influence survival at -18°C
• Cold-storage procedure reproducibility is limited by the cooling step, making practical storage impractical without specialized equipment