Microbial diversity of Toarcian argillite from Tournemire, France
Titre du congrès :ISSM 2008 - 7th International Symposium for Subsurface Microbiology
Ville du congrès :Shizuoka
Date du congrès :16/11/2008
Argillaceous media are being investigated in several countries as one of the geological formations that could possibly host an underground repository for radioactive waste due notably to their favourable hydraulic and chemical properties. The occurrence and potential effects of microbial activity on the physico-chemical environment of the disposal barriers have to be estimated in order to assess the evolution of their containment properties. The purpose of the present work is to characterise the microbial diversity of different zones of the Toarcian argillite in IRSN's Underground Research Laboratory (Tournemire, France), which presents geochemical characteristics close to those of the Callovo-Oxfordian argillite studied by the French national radioactive waste management agency (ANDRA) in Meuse/Haute-Marne. Cores were drilled in the excavation damaged zone (EDZ) and in the deeper undisturbed zone, as well as in a zone intersected by a geological fault. Subsamples were prepared in an anaerobic chamber and used to inoculate 20 different culture media under aerobic and anaerobic conditions. The results indicated that indigenous microorganisms were present in all core samples, but differed depending on the sampling depth and moisture content. Aerobic bacteria were identified in the EDZ and the wet faulted area, whereas sulfate-reducing bacteria were isolated from the wet faulted area only. Anaerobic heterotrophs were cultivated from the three zones, including the undisturbed one. More than 70 isolates were purified and identified. Analysis of 16S rRNA gene sequences showed that bacteria of the undisturbed zone can be affiliated to Bacillus species, whereas the two other sampling zones harbour more diverse microflora, including isolates closely related to taxons already characterized from deep subsurface, deep marine and polar environments.