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Physiological and Genomic Characterization of a Nitrate-Reducing Fe(II)-Oxidizing Bacterium Isolated from Paddy Soil

Hu, Min, Chen, Pengcheng, Sun, Weimin, Li, Fangbai, Cui, Jianghu
Geomicrobiology journal 2019 v.36 no.5 pp. 433-442
Cupriavidus metallidurans, X-ray diffraction, acetates, anaerobic conditions, bacteria, biomineralization, carbon, electron transfer, ferrous chloride, genes, genomics, iron, lepidocrocite, oxidation, paddy soils, ribosomal RNA, sequence analysis, sodium nitrate
In this study, a neutrophilic, heterotrophic bacterium (strain Paddy-2) that is capable of ferrous iron [Fe(II)] oxidation coupled with nitrate (NO₃⁻) reduction (NRFO) under anoxic conditions was isolated from paddy soil. The molecular identification by 16S rRNA gene sequencing identified the strain as Cupriavidus metallidurans. Strain Paddy-2 reduced 97.7% of NO₃⁻and oxidized 89.7% of Fe(II) over 6 days with initial NaNO₃ and FeCl₂ concentrations of 9.37 mM and 4.72 mM, respectively. Acetate (5 mM) was also supplied as a carbon source and an alternative electron donor. A poorly crystalline Fe(III) mineral was the main component observed after 15 days of growth in culture, whereas lepidocrocite was detected in the X-ray diffraction spectrum after 3 months of culture. The homologous genes in electron transfer during Fe(II) oxidation (cyc1, cymA, FoxY, FoxZ, and mtoD) were also identified in the genomes of strain Paddy-2 and other reported NRFO bacteria. These genes encoding c-Cyts may play a role in electron transfer during the process of NRFO. These results provide evidence for the potential of NO₃⁻ to affect Fe(II) oxidation and biomineralization in bacterium from anoxic paddy soil.