We are in the process of investigating the stability of extracted genomic DNA over time when stored at different temperatures. DNA was extracted from a Bacillus subtilis cell pellet using the QIAGEN Genomic-tip procedure as outlined in the product details. The extracted DNA was eluted in TE buffer, aliquoted and stored at 4°C or -20°C. After set periods of time over twelve months, aliquots are removed from storage and libraries prepared for sequencing using the Ligation Sequencing Kit (SQK-LSK109). Prior to sequencing, the samples were SPRI size-selected.

In Figure 1, data is presented on the effect of the different storage conditions on read N50. No impact on sequencing throughput was observed and all samples delivered 3-star performance: 8+ Gb in 48 hours on flow cell FLO-MIN106, equivalent to the Lambda DNA supplied with the Control Expansion pack (EXP-CTL001).

Figure 1. The effect of storage of DNA at -20°C or at 4°C on the observed read N50 of DNA sequencing libraries. These data indicate some deterioration of read N50 may be observed when storing DNA at 4°C over a period of 6 months. Therefore, storage at -20°C is advised to maintain sample integrity.