Microbial dynamics in the aquatic environments of a nuclear reactor

Nuclear reactors waters are typically maintained in ultrapure state and are exposed to varying levels of radiation. Despite the extremely challenging conditions, microorganisms have been previously detected in these environments. The aim of this work was to investigate the bacterial communities in different waters of the BR2 nuclear reactor at SCK CEN, with a particular focus on the basin surrounding the reactor vessel. First, we investigated the viable microbial population in various water bodies using a cultivation-based approach. This yielded an extensive strain collection of 33 bacterial species. One of the isolated strains, Sphingomonas melonis, was shown to be somewhat radiation-resistant, as it survived a radiation dose of 2.1 kGy. Next, we characterized the long-term community dynamics in the basin through 16S rRNA amplicon sequencing. This resulted in the characterization of a diverse bacterial population displaying clear shifts in community profiles: cycles of operation were mostly dominated by an unclassified Gammaproteobacterium and Pelomonas, whereas Methylobacterium prevailed during shutdowns. Finally, we studied the functional characteristics of the microbial community in the basin through shotgun metagenomics. Several pathways with a role in cell function recovery after irradiation were more highly represented during shutdowns. Furthermore, two MAGs were almost entirely reconstructed from the metagenome, namely Bradyrhizobium sp. BTAi1 and Methylobacterium sp. UNC378MF. In conclusion, we managed to uncover a large bacterial diversity in various waters of the BR2, which were shown to harbor significant evolutionary adaptations allowing them to survive in these extremely challenging environments.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 202

Cyclical Patterns Affect Microbial Dynamics in the Water Basin of a Nuclear Research Reactor

The BR2 nuclear research reactor in Mol, Belgium, runs in successive phases of operation (cycles) and shutdown, whereby a water basin surrounding the reactor vessel undergoes periodic changes in physico-chemical parameters such as flow rate, temperature, and radiation. The aim of this study was to explore the microbial community in this unique environment and to investigate its long-term dynamics using a 16S rRNA amplicon sequencing approach. Results from two sampling campaigns spanning several months showed a clear shift in community profiles: cycles were mostly dominated by two Operational Taxonomic Units (OTUs) assigned to unclassified Gammaproteobacterium and Pelomonas, whereas shutdowns were dominated by an OTU assigned to Methylobacterium. Although 1 year apart, both campaigns showed similar results, indicating that the system remained stable over this 2-year period. The community shifts were linked with changes in physico-chemical parameters by Non-metric Multidimensional Scaling (NMDS) and correlation analyses. In addition, radiation was hypothesized to cause a decrease in cell number, whereas temperature had the opposite effect. Chemoautotrophic use of H2 and dead cell recycling are proposed to be used as a strategies for nutrient retrieval in this extremely oligotrophic environment

Direct Meta-Analyses Reveal Unexpected Microbial Life in the Highly Radioactive Water of an Operating Nuclear Reactor Core

International audienceThe pools of nuclear reactor facilities constitute harsh environments for life, bathed with ionizing radiation, filled with demineralized water and containing toxic radioactive elements. The very few studies published to date have explored water pools used to store spent nuclear fuels. Due to access restrictions and strong handling constraints related to the high radioactivity level, nothing is presently known about life in water pools that directly cool nuclear cores. In this work, we investigated the microbial communities in the cooling pool of the French Osiris nuclear reactor using direct meta-omics approaches, namely, DNA metabarcoding and proteotyping based on 16S ribosomal RNA gene sequencing and on peptide analysis, respectively. We identified 25 genera in the highly radioactive core water supply during operation with radionuclide activity higher than 3 × 10 9 Bq/m 3. The prevailing genera Variovorax and Sphingomonas at operation were supplanted by Methylobacterium, Asanoa, and Streptomyces during shutdown. Variovorax might use dihydrogen produced by water radiolysis as an energy source