Cyclical patterns affect microbial dynamics in the water basin of a nuclear research reactor

Valerie Van Eesbeeck, Ruben Props, Mohamed Mysara, Pauline C. M. Petit, Corinne Rivasseau, Jean Armengaud, Pieter Monsieurs, Jacques Mahillon, Natalie Leys

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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 H-2 and dead cell recycling are proposed to be used as a strategies for nutrient retrieval in this extremely oligotrophic environment.

Original languageEnglish
Article number744115
JournalFrontiers in Microbiology
Number of pages11
Publication statusPublished - 2021


  • nuclear reactor
  • ultrapure water
  • ionizing radiation
  • 16S rRNA amplicon sequencing
  • aquatic microbiome
  • extreme environment
  • SP-NOV
  • FUEL
  • LIFE

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