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

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

doi:10.3389/fmicb.2021.744115

Abstract

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.

Highlights

Waters of nuclear facilities are constantly filtered and deionized to remove dissolved radionuclides, as well as impurities and ions that could become activated
Microbes can be present in the form of planktonic populations or biofilms, which can adhere to metal surfaces in Spent Nuclear Fuel Pools (SNFPs), potentially leading to microbiologically influenced corrosion (MIC; Zhang et al, 1999; Giacobone et al, 2011; Smart et al, 2014)
In order to study the dynamics of the bacterial community in the basin water, two sampling campaigns spanning multiple cycle and shutdown periods were performed using a 16S rRNA amplicon sequencing approach

Summary

Introduction

Waters of nuclear facilities are constantly filtered and deionized to remove dissolved radionuclides, as well as impurities and ions that could become activated They are exposed to varying levels of ionizing radiation depending on their proximity with radioactive sources (up to 40 kGy h−1 as estimated in the primary circuit of the BR2 reactor during operation). Microbes can be present in the form of planktonic populations or biofilms, which can adhere to metal surfaces in SNFPs, potentially leading to microbiologically influenced corrosion (MIC; Zhang et al, 1999; Giacobone et al, 2011; Smart et al, 2014) This phenomenon has been investigated, together with the radionuclide bioaccumulation potential of some bacterial strains (Jolley, 2002; Tisakova et al, 2013), these studies mainly focused on cultivation-based approaches at a single point in time to identify and characterize the detected microorganisms. Knowledge on the evolution of these communities over time is currently lacking

Objectives

Methods

Results

Conclusion