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

Area of Science:

• Microbiology
• Environmental Science
• Nuclear Engineering

Background:

• The BR2 nuclear research reactor in Mol, Belgium, features a unique aquatic environment subject to cyclical operational changes.
• Physico-chemical parameters like flow rate, temperature, and radiation fluctuate periodically within the reactor's water basin.

Purpose of the Study:

• To explore the microbial community within the BR2 nuclear reactor's water basin.
• To investigate the long-term dynamics of this microbial community in response to operational cycles.

Main Methods:

• 16S rRNA amplicon sequencing was employed to analyze microbial community composition.
• Non-metric Multidimensional Scaling (NMDS) and correlation analyses were used to link community shifts with environmental parameters.

Main Results:

• Distinct microbial community profiles were observed between reactor operation (cycles) and shutdown phases.
• Unclassified Gammaproteobacterium and Pelomonas dominated during cycles, while Methylobacterium was prevalent during shutdowns.
• The microbial community structure remained stable over a 2-year period, despite seasonal variations.

Conclusions:

• Microbial community composition in the BR2 reactor is strongly influenced by operational cycles and associated physico-chemical changes.
• Radiation may decrease microbial cell numbers, while increased temperature appears to promote growth.
• Chemoautotrophy and dead cell recycling are proposed as nutrient acquisition strategies in this oligotrophic environment.