Frédéric Jorand

Surface structure and nanomechanical properties of Shewanella putrefaciens bacteria at two pH values (4 and 10) determined by atomic force microscopy.

The nanomechanical properties of gram-negative bacteria (Shewanella putrefaciens) were investigated in situ in aqueous solutions at two pH values, specifically, 4 and 10, by atomic force microscopy (AFM). For both pH values, the approach force curves exhibited subsequent nonlinear and linear regimens that were related to the progressive indentation of the AFM tip in the bacterial cell wall, including a priori polymeric fringe (nonlinear part), while the linear part was ascribed to compression of the plasma membrane. These results indicate the dynamic of surface ultrastructure in response to changes in pH, leading to variations in nanomechanical properties, such as the Youngs modulus and the bacterial spring constant.

Abiotic Process for Fe(II) Oxidation and Green Rust Mineralization Driven by a Heterotrophic Nitrate Reducing Bacteria (Klebsiella mobilis)

Green rusts (GRs) are mixed Fe(II)-Fe(III) hydroxides with a high reactivity toward organic and inorganic pollutants. GRs can be produced from ferric reducing or ferrous oxidizing bacterial activities. In this study, we investigated the capability of Klebsiella mobilis to produce iron minerals in the presence of nitrate and ferrous iron. This bacterium is well-known to reduce nitrate using an organic carbon source as electron donor but is unable to enzymatically oxidize Fe(II) species. During incubation, GR formation occurred as a secondary iron mineral precipitating on cell surfaces, resulting from Fe(II) oxidation by nitrite produced via bacterial respiration of nitrate. For the first time, we demonstrate GR formation by indirect microbial oxidation of Fe(II) (i.e., a combination of biotic/abiotic processes). These results therefore suggest that nitrate-reducing bacteria can potentially contribute to the formation of GR in natural environments. In addition, the chemical reduction of nitrite to ammonium by GR is observed, which gradually turns the GR into the end-product goethite. The nitrogen mass-balance clearly demonstrates that the total amount of ammonium produced corresponds to the quantity of bioreduced nitrate. These findings demonstrate how the activity of nitrate-reducing bacteria in ferrous environments may provide a direct link between the biogeochemical cycles of nitrogen and iron.

Kinetic and Thermodynamic Analysis During Dissimilatory γ-FeOOH Reduction: Formation of Green Rust 1 and Magnetite

In laboratory experiments, lepidocrocite reduction by the dissimilatory iron reducing bacteria, Shewanella putrefaciens , is known to generate extra-cellular iron (II-III) minerals as green rust (GR) or magnetite. However, the parameters controlling the formation of these minerals remain unclear. In order to identify these parameters, reduction experiments were designed to obtain either GR or magnetite with methanoate as electron source and lepidocrocite (γ-FeOOH) as the electron acceptor. The mineral products were monitored by XRD analyses, and the rate of reduction and E h /pH evolution were assessed during GR and magnetite formation. The only difference between the two conditions lies with the inoculum size: magnetite is systematically produced by the treatments containing the lowest cell density (5 × 10 8 CFU mL −1 ) and GR1(CO 3 2− ) precipitated in the highest cell density (2 × 10 9 CFU mL −1 ). We showed that 100 μ M of anthraquinone 2,6 disulfonate (AQDS) did not influence the nature of the biogenic minerals. In addition, based on thermodynamic calculations, we observed that the E h /pH paths in the Pourbaix diagram depend on the nature of the minerals formed, i.e. GR1(CO 3 2− ) or Fe 3 O 4 . However, the Pourbaix diagram cannot be used to forecast unambiguously the nature of these minerals. We propose that a close association of bacterial cells and γ -FeOOH particles occurs during the Fe(III) mineral reduction. We hypothesis that this aggregation influences the bio-reduction rate and is related to the nature of the biogenic mineral precipitated in the reduction media.

Bacterial and iron oxide aggregates mediate secondary iron mineral formation: green rust versus magnetite

In the presence of methanoate as electron donor, Shewanella putrefaciens, a Gram-negative, facultative anaerobe, is able to transform lepidocrocite (gamma-FeOOH) to secondary Fe (II-III) minerals such as carbonated green rust (GR1) and magnetite. When bacterial cells were added to a gamma-FeOOH suspension, aggregates were produced consisting of both bacteria and gamma-FeOOH particles. Recently, we showed that the production of secondary minerals (GR1 vs. magnetite) was dependent on bacterial cell density and not only on iron reduction rates. Thus, gamma-FeOOH and S. putrefaciens aggregation pattern was suggested as the main mechanism driving mineralization. In this study, lepidocrocite bioreduction experiments, in the presence of anthraquinone disulfonate, were conducted by varying the [cell]/[lepidocrocite] ratio in order to determine whether different types of aggregate are formed, which may facilitate precipitation of GR1 as opposed to magnetite. Confocal laser scanning microscopy was used to analyze the relative cell surface area and lepidocrocite concentration within the aggregates and captured images were characterized by statistical methods for spatial data (i.e. variograms). These results suggest that the [cell]/[lepidocrocite] ratio influenced both the aggregate structure and the nature of the secondary iron mineral formed. Subsequently, a [cell]/[lepidocrocite] ratio above 1 x 10(7) cells mmol(-1) leads to densely packed aggregates and to the formation of GR1. Below this ratio, looser aggregates are formed and magnetite was systematically produced. The data presented in this study bring us closer to a more comprehensive understanding of the parameters governing the formation of minerals in dense bacterial suspensions and suggest that screening mineral-bacteria aggregate structure is critical to understanding (bio)mineralization pathways.

Formation of Hydroxysulphate Green Rust 2 as a Single Iron(II-III) Mineral in Microbial Culture

Although GR2(SO4 2-) can be easily formed by abiotic synthesis, the biotic formation of hydroxysulphate as a single iron(II-III) mineral in microbial culture and its characterization was not achieved. This study was carried out to investigate the sole formation of GR2(SO4 2-) during the reduction of γ-FeOOH by a dissimilatory iron-respiring bacterium, Shewanella putrefaciens CIP 8040T. Reduction experiments were performed in a non-buffered medium devoid of organic compounds, with 25 mM of sulphate and with a range of lepidocrocite concentrations with H2 as the electron donor under nongrowth conditions. The resulting biogenic solids, after iron-respiring activity, were characterized by X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and electron microscopy (SEM and TEM). The sulphate has been identified as the intercalated anion by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In addition, the structure of this sulphate anion was discussed. Our experimental study demonstrated that, under H2 atmosphere, the biogenic solid was a GR2(SO4 2-), as the sole iron(II-III) bearing mineral, whatever the initial lepidocrocite concentration. The crystals of the biotically formed GR2(SO4 2-) are significantly larger than those observed for GR2(SO4 2-) obtained through abiotic preparation, < 15 μ m diameter as against 0.5–4 μm, respectively.

Competitive Formation of Hydroxycarbonate Green Rust 1 versus Hydroxysulphate Green Rust 2 in Shewanella putrefaciens Cultures

The formation of hydroxysulphate green rust 2, a Fe(II-III) compound commonly found during corrosion processes of iron-based materials in seawater, has not yet been reported in bacterial cultures. Here we used Shewanella putrefaciens, a dissimilatory iron-reducing bacterium to anaerobically catalyze the transformation of a ferric oxyhydroxide, lepidocrocite (γ-FeOOH), into Fe(II) in the presence of various sulphate concentrations. Biotransformation assays of γ-FeOOH were performed with formate as the electron donor under a variety of concentrations. The results showed that the competitive formation of hydroxycarbonate green rust 1 (GR1(CO3 2−)) and hydroxysulphate green rust 2 (GR2(SO4 2 −)) depended upon the relative ratio (R) of bicarbonate and sulphate concentrations. When R ≥ 0.17, GR1(CO3 2 −) only was formed whereas when R < 0.17, a mixture of GR2(SO4 2 −) and GR1(CO3 2 −) was obtained. These results demonstrated that the hydroxysulphate GR2 can originate from the microbial reduction of γ-FeOOH and confirmed the preference for carbonate over sulphate during green rust precipitation. The solid phases were characterized by X-ray diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy. Diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of intercalated carbonate and sulphate in green rusts structure. This study sheds light on the influence of dissimilatory iron-reducing bacteria on microbiologically influenced corrosion.

Advantage Provided by Iron for Escherichia coli Growth and Cultivability in Drinking Water

ABSTRACT The presence of iron, used both as a nutrient and as an electron acceptor, was demonstrated to give an advantage to Escherichia coli bacteria in drinking water. Slight additions of ferrous sulfate to water with initial low iron concentrations led to a significant increase in the number of E. coli bacteria. The presence of ferric oxide in water under anaerobic conditions increased bacterial cultivability.

Key role of the kinetics of γ-FeOOH bioreduction on the formation of Fe(II–III) minerals

During bacterial reduction of γ-FeOOH lepidocrocite in the presence of formate as electron donor at initial pH 7.5 in bicarbonate buffer, the obtained Fe(II–III) minerals were characterised by transmission Mossbauer spectroscopy (TMS) and X-ray diffraction (XRD). Two types of kinetics, high and slow, of γ-FeOOH bioreduction were obtained. The high rate of ferric oxyhydroxide reduction produced magnetite whereas the slow rate yielded hydroxycarbonate green rust.

Reduction of ferric green rust by Shewanella putrefaciens

Aims:  To reduce carbonated ferric green rust (GR*) using an iron respiring bacterium and obtain its reduced homologue, the mixed FeII–FeIII carbonated green rust (GR).

Microbial Reduction of Lepidocrocite γ-FeOOH by Shewanella putrefaciens; The Formation of Green Rust

Dissimilatory iron-reducing bacteria (DIRB) couple the oxidation of organic matter or H2 to the reduction of iron oxides. The bacterial reduction of a most common well-crystallised ferric oxyhydroxide, γ-FeOOH was investigated using DIRB Shewanella putrefaciens, strain CIP 8040. Experiments were conducted in the presence of neither organic buffer nor phosphate, with formate as electron donor, bicarbonate, and anthraquinone-2,6-disulfonate (AQDS, a humic acid analogue) that influenced the extent of ferric oxide bioreduction. The production of Fe2+ was followed with time. The solid phases obtained after bacterial iron reduction were analysed by transmission Mossbauer spectroscopy (TMS) and X-ray diffraction (XRD). Biogenic formation of green rust 1 compound, which contains carbonate anions, [FeII2FeIII2(OH)8]2+⋅[CO32−]2− was observed. TMS was used to follow the evolution of the green rust abundance during the bacterial culture.