Biogenic minerals formation by an Fe(III)-reducing Desulfitobacterium sp. isolate

Dissimilatory iron reduction is an anaerobic respiratory pathway, wherein ferric (Fe(III)) reducers couple the oxidation of organic acids, sugars and aromatic hydrocarbons to the reduction of Fe(III)-species [1]. This may lead to the formation of minerals such as magnetite (Fe(II)Fe(III)₂O₄) and siderite (Fe(II)CO₃) [2], which, in turn, can mediate the reduction of soluble pollutants as pertechnetate (Tc(VII)O₄⁻) to insoluble oxides (Tc(IV)O₂) [3].
The genus Desulfitobacterium contains obligate anaerobic bacteria that are capable of utilizing a wide range of electron acceptors, including nitrite, sulfite, metals, humic acids and halogenated organic compounds [4].
In this work, the Fe(III) reduction of a Desulfitobacterium species was examined. The microorganism has been isolated from bentonite, which is potentially used as geotechnical barrier in deep geological repositories for radioactive waste [5].
The cultivation conditions included DSMZ 579 medium with Na-acetate as electron donor to reduce Fe(III) citrate [6]. During cultivation, the formation of white precipitates was observed. The phases were collected both under aerobic and anaerobic conditions and repeatedly investigated by using Raman microscopy and powder X-ray diffraction (pXRD). It was noticed that the phases turned immediately to blue-greenish overnight under oxic conditions. Both Raman spectra and pXRD diffractograms can be attributed to vivianite (Fe(II)₃(PO₄)₂). Moreover, Raman spectra revealed the possible presence of pyrite (Fe(II)S₂), siderite, magnetite and hematite (FeIII₂O₃). These results suggest the ability of the bacterium of forming different Fe(II)-minerals. Notwithstanding, both methods indicate the change of the chemistry of the precipitates according to environmental factors. The Fe(II)-minerals formation by this microorganism depending on Fe(III)-compounds and background electrolytes is currently ongoing. The biogenic ferrous minerals will be studied regarding the reduction of Tc(VII)O₄⁻.

The authors acknowledge the German Federal Ministry of Education and Research (BMBF) for the financial support of NukSiFutur TecRad young investigator group (02NUK072).

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[2] Lee, et al., 2007, Geomicrobiology Journal, 24:1, 31-41
[3] Lloyd, et al., 2000, Appl Environ Microbiol., 66(9):3743-9
[4] Villemur et al., 2006, FEMS Microbiol Rev. 2006, 30(5):706-33
[5] Drozdowski J., et al., 2018, HZDR Annual Report, pp. 40, ISSN 2191-870
[6] https://www.dsmz.de/microorganisms/medium/pdf/DSMZ_Medium579.pdf. Accessed on 27.02.23