Evaluation of Two Matrices for Long-Term, Ambient Storage of Bacterial DNA

Culture-independent molecular analyses allow researchers to identify diverse microorganisms. This approach requires microbiological DNA repositories. The standard for DNA storage is liquid nitrogen or ultralow freezers. These use large amounts of space, are costly to operate, and could fail. Room temperature DNA storage is a viable alternative. In this study, we investigated storage of bacterial DNA using two ambient storage matrices, Biomatrica DNAstable^® Plus and GenTegra^® DNA.

We created crude and clean DNA extracts from five Streptococcus pneumoniae isolates. Extracts were stored at -30°C (our usual DNA storage temperature), 25°C (within the range of temperatures recommended for the products), and 50°C (to simulate longer storage time). Samples were stored at -30°C with no product and dried at 25°C and 50°C with no product, in Biomatrica DNAstable Plus or GenTegra DNA. We analyzed the samples after 0, 1, 2, 4, 8, 16, 32, and 64 weeks using the Nanodrop 1000 to determine the amount of DNA in each aliquot and by real-time PCR for the S. pneumoniae genes lytA and psaA. Using a 50°C storage temperature, we simulated 362 weeks of 25°C storage.

The average amount of DNA in aliquots stored with a stabilizing matrix was 103%-116% of the original amount added to the tubes. This is similar to samples stored at -30°C (average 102%-121%). With one exception, samples stored with a stabilizing matrix had no change in lytA or psaA cycle threshold (Ct) value over time (Ct range ≤2.9), similar to samples stored at -30°C (Ct range ≤3.0). Samples stored at 25°C with no stabilizing matrix had Ct ranges of 2.2-5.1.

DNAstable Plus and GenTegra DNA can protect dried bacterial DNA samples stored at room temperature with similar effectiveness as at -30°C. It is not effective to store bacterial DNA at room temperature without a stabilizing matrix.