Interaction between ferrihydrite and nitrate respirations by Shewanella oneidensis MR-1

Abstract

Shewanella oneidensis MR-1 is a model dissimilatory iron reducing bacterium and plays an important role in bioremediation and biogeochemical cycling of elements. Understanding the potential interaction between iron and nitrate respirations by S. oneidensis MR-1 is of great significance for environmental bioremediation. In this paper, the stimulating effect of nitrate on iron reduction by S. oneidensis MR-1 was reported, which was different from previous reports. Nitrate at environmentally relevant concentrations (e.g., <2mM) significantly enhanced the reduction of iron oxides, while nitrate at a higher concentration was detrimental to such a reduction. In the absence of nitrate, mutants of ΔnapB and ΔnrfA exhibited a more rapid iron oxides reduction than the wild type strain (WT). In the presence of 2mM nitrate, ΔnapB showed a promoted reduction ability, but ΔnrfA completely lost such a capability. Furthermore, after dosing 2mM nitrate, both WT and ΔnapB generated more ATP while ΔnrfA exhibited a reduced ATP production. This study demonstrates that nitrate respiration affected iron respiration of S. oneidensis MR-1 in a complex manner and its nitrate- and iron-respiration properties endowed this strain a great flexibility and adaptability to the fluctuation and availability of nitrate and iron.