Soil conservation for DNA preservation for bacterial molecular studies

The aim of this study was to select a method for preserving bacterial DNA i n soil samples in cases where there are no possibilities of using freezing or cooling methods. To overcome this difficulty, we hypothesized that addin g absolute ethanol to soil samples could be as successful to preserve bacte ria as it is to preserve insect or tissue samples for molecular studies. Ln an attempt to test this assumption, we compared four conservation conditio ns. After inoculation of soil samples with Escherichia coli, they were eith er kept at 28 degrees C, stored in the cold (4 degrees C), dried at 60 degr ees C, or treated with absolute ethanol. The relative effectiveness of the methods was evaluated by using both DNA recoveries and bacterial 16S rDNA a mplification as criteria. Two kinds of soils, i.e. sandy clay and clayey so il, were used. Soil conservation was tested for seven time periods ranging from 2 d to 1 year after bacterial inoculation. Results showed that cold co nservation or addition of absolute ethanol to the samples yielded similar D NA recoveries. For these treatments, successful amplifications are still ob tained after one year of conservation. The ethanol conservation of soil sam ples appears to be the easiest method to preserve the bacterial DNA because of its reliability and field convenience. (C) 2000 Editions scientifiques et medicales Elsevier SAS.