The Science Behind Bacterial Storage

Bacteria, like all living organisms, require nutrients and optimal environmental conditions to grow and reproduce. Under starvation conditions, where nutrients are scarce or absent, the survival of bacteria depends heavily on the storage environment, particularly temperature.

Storage at 37°C

• 37°C is the optimal growth temperature for many pathogenic and laboratory bacteria, such as Escherichia coli.

• At this temperature, bacteria remain metabolically active, rapidly consuming any available resources.

• Under starvation at 37°C, bacteria quickly deplete their internal reserves, leading to cell death and loss of viability.

Storage at 4°C

• 4°C is a refrigeration temperature that significantly slows down bacterial metabolism.

• At this low temperature, the biochemical processes inside bacterial cells are drastically reduced.

• Bacteria enter a dormant or near-dormant state, conserving energy and resources, which enhances their survival under nutrient-limited conditions.

The Key Reason: Lowered Metabolic Activity

The main reason bacteria are best stored under starvation at 4°C rather than 37°C is:

(2) Overall metabolic activity is lowered

By lowering the temperature to 4°C, the metabolic activities of bacteria are suppressed. This means:

• Reduced consumption of internal energy reserves.

• Slower cellular processes, minimizing damage and prolonging survival.

• Lower risk of mutations and genetic drift compared to higher temperatures.

Why Not the Other Options?

• (1) Membrane freezes: At 4°C, bacterial membranes do not freeze; freezing occurs at much lower temperatures (below 0°C).

• (3) Increases enzyme efficiency: Low temperatures actually decrease enzyme efficiency, which is beneficial for storage, not for active growth.

• (4) Large mortality so low competition: The goal is to minimize mortality, not increase it.

Practical Applications

• Short-term storage: Bacterial cultures are often kept at 4°C on agar slants or in broth for days to weeks.

• Long-term storage: For months to years, bacteria are typically frozen at -80°C or lyophilized (freeze-dried).

Conclusion

Storing bacteria under starvation at 4°C is more effective than at 37°C because overall metabolic activity is lowered, allowing cells to survive longer with minimal resources.

Correct answer:
(2) Overall metabolic activity is lowered