Geomicrobial Identification of Two Indian Bentonites and Their Impact on Barrier Performance for Disposal of Nuclear Waste

Abstract

In the long-term operation of any deep geological repository (DGR), microbial species can grow within and biological activity may take place. The presence of microbes can result in the production of small organic acids and siderophores that may change the properties of the buffer material and corrode the metal canisters. In the current study, the bacterial population of Bikaner and Barmer bentonites was investigated through the plate culture technique. For detailed analysis, 16S ribosomal RNA (rRNA) gene sequencing technique was carried out. The results showed that Bacillus tequilensis KTCT 13622(T) and Lysinibacillus fusiformis NBRC 15717(T) were present in the Bikaner bentonite, whereas Burkholderia contaminans LMG 23361(T) and Staphylococcus pasteuri ATCC 51129(T) were present in the Barmer bentonite. Bacillus tequilensis and Lysinibacillus fusiformis are rod-shaped, gram-positive, nonmoveable bacteria of phylum Firmicutes. Burkholderia contaminans is a gram-negative, rod-shaped, moveable bacterium of phylum Proteobacteria. Staphylococcus is a genus of gram-positive bacteria in phylum Firmicutes. Bacteria belonging to the phylum Firmicutes can restrict the mobility of toxic radionuclides by the process of biosorption; and bacteria belonging to the phylum Actinobacteria have the ability to change their shape by extending out branches, or filaments, and destabilizing the compactness of the backfill material. The identified bacteria would be helpful for designing DGRs, considering the long-term safety aspects.