Impact of radionuclides and radiation on bacterial populations in the contaminated soil of Chernobyl
Nicolas Thédorakopoulos has defended his thesis on 20th December 2013 in Cadarache.
The nuclear power plants accidents of Chernobyl and Fukushima
demonstrate the importance of the understanding of the transfer of the
radioactive contamination in the environment and its ecological consequences.
Although certain studies have been realized on superior organisms of the food
chain, studies on telluric bacterial communities are scarce. The latter play
nevertheless an essential role in the mobility of contaminants in soils by
decreasing or improving their transfer towards other compartments (water,
vegetables and animals). Moreover radionuclides (RNs) can have toxic effects on
bacteria, leading to an inhibition of their participation in such transfer. The
objectives of this study were (1) to estimate the impact of the radioactive
contamination on bacterial communities belonging to a soil of the Chernobyl
exclusion zone (trench T22) and (2) to study the uranium-bacteria interactions
of a resistant strain, isolated from this soil. The various techniques used to
characterize the bacterial diversity (culture of bacteria, DGGE, 454
pyrosequencing) all testified of the multiplicity and the abundance of the
bacterial communities in spite of the contamination. An impact on the community
structure was difficult to assess by DGGE or cultural approach, but was
nevertheless highlighted by the use of pyrosequencing, suggesting the presence
of species more adapted to the contaminated soil conditions. A specific
molecular tool dedicated to the search of bacteria affiliated to the known
radiation resistant Deinococcus-Thermus phylum (for example the Deinococcus
radiodurans specie survives after an irradiation of several kGy) was developed.
However it did not reveal the presence of bacteria affiliated to such a phylum
in the studied soil. In parallel to the study of the bacterial biodiversity,
about fifty culturable bacteria were isolated from this site and were used as a
support to select a species (Microbacterium) capable to survive strong U(VI)
concentrations. The characterization of the interactions between the selected
bacteria isolate (Microbacterium) and U(VI) highlighted an active mechanism of
detoxification which involves an efflux of the U(VI) entering the cell and an
intracellular precipitation of U(VI) in form of autunite.