Bacterial diversity in bentonites, engineered barrier for deep geological disposal of radioactive wastes

The long-term disposal of radioactive wastes in a deep geological repository is the accepted international solution for the treatment and management of these special residues. The microbial community of the selected host rocks and engineered barriers for the deep geological repository may affect the performance and the safety of the radioactive waste repository. In this work the bacterial community of bentonite formations of Almeria (Spain), selected as reference material for bentonite engineered barriers in the disposal of radioactive wastes, was studied. 16S rRNA gene-based approaches were used to study the bacterial community of the bentonite samples by traditional clone libraries and Illumina-sequencing. A high bacterial diversity was found by both techniques, with phylotypes belonging to 13 different bacterial phyla: Acidobacteria, Actinobacteria, Armatimonadetes, Bacteroidetes, Choloroflexi, Cyanobacteria, Deinococcus-Thermus, Firmicutes, Gemmatimonadetes, Planctomycetes, Proteobacteria, Nitrospirae and Verrucomicrobia. The dominant groups of the community were mainly represented by Proteobacteria and Bacteroidetes.
Some of the identified genera were previously described for their capacity to interact with iron and different heavy metals as well as radionuclides, as for example, Acidovorax, Ralstonia, Variovorax and Sphingomonas. The results obtained in this work demonstrate the high bacterial diversity of these Spanish bentonite formations, and their possible negative effect on the structure of the clay minerals as well as interactions with different radionuclides, which may affect the safety of the deep geological repository of radioactive wastes.