Adverse Effect of Air Exposure on the Stability of DNA Stored at Room Temperature

In view of the exponential increase of the number of DNA samples to be stored, classical conservation in freezers appears cumbersome and costly and may be subjected to the risks of natural disasters. Room temperature storage of dehydrated DNA emerges as an alternative solution because the main degradation pathways (depurination, base deamination, and base or sugar oxidation) of DNA involve water, solid state is known to generally slow down chemical processes because of reduction of molecular mobility, and there are multiple examples of retrieval of DNA aged at room temperature. However, DNA, even thoroughly dried, if left exposed to air, regains a fair amount of water and still undergoes strand breaking and oxidation. Moreover, the presence of the atmospheric pollutant ozone, very reactive toward DNA, should not be neglected. Thus, it appears that long-term storage of DNA at room temperature may require an absolute protection from the atmosphere. However, this protection cannot be provided by plastic containers because they are known to be permeable to moisture vapor. We therefore developed a new procedure for room temperature storage of DNA wherein DNA samples are stored under an anoxic and anhydrous atmosphere in small glass vials fitted in stainless-steel, laser-sealed capsules. Under these conditions, at room temperature or 70 degrees C, no DNA degradation was detected after 8-month or 1-week storage, respectively, whereas samples kept in air in closed plastic tubes, either naked or in the presence of matrices, underwent clear or strong degradation and/or aggregation. This study demonstrates the necessity of protecting DNA from air to preserve its integrity for room temperature storage.