Metagenomic analysis of heavy water-adapted bacterial communities

Micro-organisms can survive and thrive in unusual and extreme environments. Here, we present a metagenomic analysis of living bacteria found in highly pure, deleterious heavy water (>99% D₂O), stored in sealed plastic containers for more than 30 years, without any external supply. Deep DNA sequencing analyses have revealed that the most abundant genetic signatures were primarily associated with Pseudomonadota and Bacteroidota. These bacteria exhibited shorter gene lengths and depletion of polar and metabolically costly amino acids compared to the related species from light water environments. Genes related to DNA transposition, repair and modification were notably abundant, particularly mutant forms of the IS3 transposable elements family. We also explore potential carbon and energy sources and discuss the evolutionary implications of bacteria capable of surviving in such an extreme human-made environment.