DNA perseverance of microorganisms exposed to silica: an experimental study

The persistence of DNA from microorganisms exposed to various concentrations of SiO2 (ranging from 0 to 3000 p.p.m.) was monitored over time. The impact of silica mineralization or silicification on the longevity of 16S rRNA and 16 s rDNA genes from whole cells of Bacillus subtilis and Escherichia coli K12 was quantified using real-time polymerase chain reaction (RT-PCR), and cells were visualized using optical microscopy. For B. subtilis, DNA longevity decreased in experiments with higher levels of SiO2 (1000 and 3000 p.p.m.), in comparison to zero or low (100 p.p.m.) levels. For B. subtilis, cell viability was greatest in the absence of silica, and markedly decreased in the presence of any concentration of silica. Survival of Escherichia coli cells, on the other hand, was not sensitive to silica in the solution. All cells died at similar rates over the 180 days they were monitored, decreasing to about 1% survival. DNA longevity for E. coli did appear to be enhanced to some degree by the presence of 1000 p.p.m. silica, but higher or lower concentrations showed no increased longevity in comparison to the no-silica control. Overall, findings of this study do not support the hypothesis that siliceous environments provide enhanced protection and preservation of DNA over time. However, results of this study do provide guidelines on the persistence of DNA that might be expected in modern silica-rich environments, which may be an important factor for proper characterization of present-day microbial communities.