The colonization of an irradiated environment: the case of microbial biofilm in a nuclear reactor

Abstract

The investigation of the microbial community change in the biofilm, growing on the walls of a containment tank of TRIGA nuclear reactor revealed a thriving community in an oligotrophic and heavy-metal-laden environment, periodically exposed to high pulses of ionizing radiation (IR). We observed a vertical IR resistance/tolerance stratification of microbial genera, with higher resistance and less diversity closer to the reactor core. One of the isolated Bacillus strains survived 15 kGy of combined gamma and proton radiation, which was surprising. It appears that there is a succession of genera that colonizes or re-colonizes new or IR-sterilized surfaces, led by Bacilli and/or Actinobacteria, upon which a photoautotrophic and diazotrophic community is established within a fortnight. The temporal progression of the biofilm community was evaluated also as a proxy for microbial response to radiological contamination events. This indicated there is a need for better dose-response models that could describe microbial response to contamination events. Overall, TRIGA nuclear reactor offers a unique insight into IR microbiology and provides useful means to study relevant microbial dose-thresholds during and after radiological contamination.

Graphical Abstract

Keywords:

• Microbial biofilm
• radiation microbiology
• research reactor
• ionizing radiation
• radioecology
• bacterial microbiome

Acknowledgements

The authors acknowledge the financial support from the Slovenian Research Agency for Research Core Funding No. (P2-0073) and support to “Infrastructural Centre Microscopy of Biological Samples” (MRIC UL, I0-0022-0481-08) at Biotechnical Faculty, University of Ljubljana, which provided microscopic service. TT was funded by the Slovenian Research Agency (Research Core Funding No. P1-0237). We gratefully acknowledge help of Ricardo Pedroza with Figure 6. SL gratefully acknowledges financial support from P1-0143 (Slovenian Research Agency).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors acknowledge the financial support from the Slovenian Research Agency for Research Core Funding No. (P2-0073). TT was funded by the Slovenian Research Agency (Research Core Funding No. P1-0237).

Notes on contributors

Arne Bratkic

Arne Bratkic is a marine biogeochemist, focused on interactions between microbes and trace elements. He is interested particularly in iron and other biogenic metals’ bioavailability, their connection with carbon cycle and the implications these have in the changing global Ocean. Arne has developed new tracers of iron redox biogeochemistry and is now Scientific Associate at the National Institute of Biology - Marine Biology Station in Slovenia.

Anze Jazbec

Anze Jazbec is shift supervisor at Jožef Stefan Institute TRIGA research reactor. He is responsible for the modifications and modernization of the reactor. Anze helps researchers to set up and license new experiments and new experimental devices at the reactor.

Natasa Toplak

Natasa Toplak: During her PhD at the National Institute of Biology in Ljubljana, Natasa Toplak, PhD, explored genetic resistance mechanisms in transgenic potato plants using novel molecular techniques. Natasa now works in a private company, assisting customers with training and application support for advanced molecular technologies, specializing in next-gen sequencing, qPCR, and digital PCR.

Simon Koren

Simon Koren: After finishing PhD in monoclonal antibody / prion disease research, Simon Koren continued his career in a private company, where he is supporting customers through sales, training, and application support. Continuing hands-on laboratory experience and research, in recent years mainly focused on next-generation sequencing and metagenomics.

Sonja Lojen

Sonja Lojen is interested in isotope ecology and geochemistry. Currently, she is a research counselor at the Jozef Stefan Institute and an associate professor at the University of Nova Gorica in Slovenia.

Tinkara Tinta

Tinkara Tinta is a marine microbial ecologist investigating microbial community dynamics during natural and anthropogenic perturbations in marine environment. Her research focuses on the interactions between bacteria and jellyfish and the implications for the biogeochemical cycles in the ocean. She has a multidisciplinary scientific background with B.Sc. in Biochemistry and Ph.D. in Environmental Sciences with more than 10 years of full-time research experience in the field of marine microbial ecology.

Rok Kostanjsek

Prof. dr. Rok Kostanjsek - full professor of zoology, Head of Chair of zoology at the Department of Biology, Biotechnical Faculty, University of Ljubljana and head of Infrastructure Center for Microscopy of Biological Samples, which operates within the network of infrastructure centers of the University of Ljubljana.

Luka Snoj

Luka Snoj is head of TRIGA reactor, head of reactor physics division at the Jozef Stefan Institute and associate professor at the Faculty of Mathematics and physics, University of Ljubljana. His research interest is mainly theoretical reactor physics related to practical applications in power and research reactors, in particular: Monte Carlo transport of neutrons and photons in fission and fusion nuclear reactors.