In situ bacterial colonization of compacted bentonite under deep geological high-level radioactive waste repository conditions

Abstract

Subsurface microorganisms are expected to invade, colonize, and influence the safety performance of deep geological spent nuclear fuel (SNF) repositories. An understanding of the interactions of subsurface dwelling microbial communities with the storage is thus essential. For this to be achieved, experiments must be conducted under in situ conditions. We investigated the presence of groundwater microorganisms in repository bentonite saturated with groundwater recovered from tests conducted at the Aspö underground Hard Rock Laboratory in Sweden. A 16S ribosomal RNA and dissimilatory bisulfite reductase gene distribution between the bentonite and groundwater samples suggested that the sulfate-reducing bacteria widespread in the aquifers were not common in the clay. Aerophilic bacteria could be cultured from samples run at <or=55 degrees C but not at >or=67 degrees C. Generally, the largely gram-negative groundwater microorganisms were poorly represented in the bentonite while the gram-positive bacteria commonly found in the clay predominated. Thus, bentonite compacted to a density of approximately 2 g cm(-3) together with elevated temperatures might discourage the mass introduction of the predominantly mesophilic granitic aquifer bacteria into future SNF repositories in the long run.

Bacterial diversity and production of sulfide in microcosms containing uncompacted bentonites

“…In general, these organisms would be active when residual oxygen is present in microcosms. Similar aerobic bacilli and pseudomonads have been identified elsewhere in studies of dense bentonite blocks ( Fru and Athar, 2008 ; Jalique et al., 2016 ), indicating that these microorganisms may proliferate in DGR buffers to some extent under oxic conditions following repository closure.…”

“…Taken together, this study, along with recent discoveries of bacteria of the genera Desulfosporosinus, Sedimentibacter, Bacillus, Paenibacillus, Pseudomonas and Tissierella in highly-compacted MX-80 ( Fru and Athar, 2008 ; Persson et al., 2011 ; Jalique et al., 2016 ), not only indicates that microorganisms of these taxa are ubiquitous in commercial Wyoming bentonite, but also suggests the potential for these prokaryotes to exist transiently during evolution of conditions in the DGR ( e.g., when sufficient pore space, water, energy and carbon sources are available). The majority of discovered bacteria shared a similar metabolic capacity to obtain energy primarily via fermentation, rather than respiration.…”

“…The prevalence of Desulfosporosinus spp. in microcosms with MX-80 bentonites has previously been reported ( Fru and Athar, 2008 ; Persson et al., 2011 ).…”

Validating DNA Extraction Protocols for Bentonite Clay

“…Indeed, no or very small amounts of DNA have been recovered even from spiked clay samples (12, 16). Nonetheless, Chi Fru and Athar (17) extracted DNA from MX-80 bentonite using an optimized phenol-chloroform method and generated a clone library for analysis. Lopez-Fernandez and colleagues (18) extracted DNA from Spanish bentonite deposits with up to 96% montmorillonite using a gentle sodium dodecyl sulfate (SDS) lysis method with polyethylene glycol precipitation and a final purification using a silica-based column.…”

The geomicrobiology of CO2 geosequestration: a focused review on prokaryotic community responses to field-scale CO2 injection

“…Furthermore, increasing consideration should be placed on incorporating the potential impacts derived from operational-dependent engineering , such as the emplacement of injection and sampling wells, into the analysis pipeline, as these can influence subsurface microbial community composition and function (Morozova et al, 2011 ; Bordenave et al, 2012 ; Lavalleur and Colwell, 2013 ; Mu et al, 2014 ). The same principles of systems biology apply to the study of many other subsurface environments, such as hydrocarbon rich reservoirs (Dojka et al, 1998 ; Golby et al, 2011 ; Joshi et al, 2014 ) and radioactive waste storage sites (Nazina et al, 2004 ; Chi Fru and Athar, 2008 ).…”