The detection of a viable bacterial community in high-purity heavy water (D₂O), stored for over 30 years in hermetically sealed containers, raised a fundamental question: how these microorganisms were able to survive, and even remain active, in an environment apparently devoid of external energy sources. One of the hypotheses put forward is that the products of secondary cosmic radiation (gamma rays, muons and neutrons), or the interactions of this radiation with the D₂O itself, may provide sufficient energy to maintain the viability of this microbial community.
To test this hypothesis, a long-term experiment was launched at the LSC in 2022, comparing the evolution of bacterial communities incubated under very low-radiation conditions with samples kept at the surface and various experimental controls. Although the first study encountered methodological limitations that prevented the precise quantification of bacterial abundance due to the formation of cell aggregates, the results revealed changes in the composition and dynamics of the microbial communities, as well as greater genetic diversity than expected.
The conclusions drawn have enabled the experiment to be redesigned and a new phase to be proposed, aimed at determining more precisely the effect of reduced radiation on survival, the structure of bacterial communities and the molecular mechanisms which could explain their adaptation to extreme energy conditions.