Summary Pertechnetate, 99 Tc(VII)O 4 – , is a highly mobile radionuclide contaminant at US Department of Energy sites that can be enzymatically reduced by a range of anaerobic and facultatively anaerobic microorganisms, including Shewanella oneidensis MR‐1, to poorly soluble Tc(IV)O 2(s) . In other microorganisms, Tc(VII)O 4 – reduction is generally considered to be catalysed by hydrogenase. Here, we provide evidence that alth...