Iron reducing bacteria reduce ferric iron to ferrous iron under anaerobic conditions. One of the first studies that studied iron fractionation in iron-reducing bacteria studied the bacterium Shewanella algae. S. algae was grown on a ferrihydrite substrate, and was then allowed to reduce iron. The study found that S. algae preferentially reduced Fe over Fe, with a δFe value of -1.3‰.
More recent experiments have studied the bacterium Shewanella putrefaciens and its reduction of Fe(III) in goethite. These studies have found δFe values of -1.2‰ relative to the goethite. The kinetics of this fractionation were also studied in this experiment, and it was suggested that the iron isotope fractionation is likely related to the kinetics of the electron transfer step.
Most studies of other iron reducing bacteria have found δFe values of approximately -1.3‰. At high Fe(III) reduction rates, δFe values of -2 – -3‰ relative to the substrate have been observed. The study of iron isotopes in iron reducing bacteria enable the development of an improved understanding regarding the metabolic processes operating in these organisms.