Multidimensional exploration of Tc(VII) bio-reduction: Kinetics and cellular responses

Technetium-99 (⁹⁹Tc) is a long-lived radionuclide that poses significant environmental concerns due to its high mobility, which allows it to persist and spread in contaminated ecosystems. Among the various factors influencing its fate, microbial processes have garnered increasing attention. In this study, we assessed the effects of various environmental conditions on the kinetics of Tc(VII) bio-reduction and, for the first time, investigated the cellular responses triggered by Tc(VII) exposure through multi-omics analysis, with Bacillus cereus strain X-68 (B. cereus X-68) serving as a model organism. The results demonstrated that Tc(VII) could be reduced and accumulated within the cells as amorphous Tc(IV) hydrate by B. cereus X-68 under anaerobic conditions via a pH- and temperature-dependent enzymatic process, with key enzymes localized in the cytosol. Notably, electron transport mediators such as anthraquinone-2-sulfonate (AQS) and riboflavin significantly enhanced the reduction, emphasizing the importance of electron transfer efficiency. The accumulation of Tc in cells over time followed the two-compartment accumulation model. Furthermore, Tc(VII) exposure led to the downregulation of pathways associated with transcription, translation, cell division, chemotaxis, and colonization. Among these, Tc-triggered oxidative stress caused metabolic reprogramming, particularly in the TCA cycle, glycolysis, and proline metabolism, which enhanced NADH/NADPH synthesis, creating favorable conditions for Tc(VII) reduction. These findings elucidate the biochemical mechanisms underlying Tc-microbe interactions and provide valuable insights for developing strategies to assess and mitigate radioactive contamination in the environment.