Optimal storage conditions for highly dilute DNA samples: a role for trehalose as a preserving agent.

DNA extraction from trace samples or noninvasively collected samples often results in the recovery of low concentration solutions of DNA that are prone to DNA degradation or other loss. Because of the difficulty in obtaining such samples, and their potentially high value in wildlife and forensic studies, it is critical that optimal methods are employed for their long-term storage. We assessed the amplification yield of samples kept under different storage conditions with the addition of potential preserving agents. We stored dilutions of known concentration human placental DNA, and gorilla fecal DNA, under four conditions (+4 degrees C, -20 degrees C, -80 degrees C, dry at room temperature), and with three additives (Tris EDTA (TE) buffer, Hind III digested Lambda DNA, trehalose). The effectiveness of the treatment methods was tested at regular intervals using qPCR to assess the quantity of amplifiable DNA, and a PCR assay of a larger 757 bp fragment to evaluate the quality of that remaining DNA. The highest quantity of DNA remained in samples stored at -80 degrees C, regardless of storage additives, and those dried at room temperature in the presence of trehalose. Surprisingly, DNA quality was best preserved in the presence of trehalose, either dried or at -80 degrees C; significant quality loss occurred with -20 degrees C and +4 degrees C storage.