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.