N. I. Chistyakova

Investigations of Iron Minerals Formed by Dissimilatory Alkaliphilic Bacterium with 57Fe Mössbauer Spectroscopy

Anaerobic alkaliphilic bacterium of Geoalkalibacter ferrihydriticus type (strain Z‐0531), isolated from a bottom sediment sample from the weakly mineralized soda Lake Khadyn, have been analyzed. The strain uses the amorphous Fe(III)‐hydroxide (AFH) as an electron acceptor and acetate CH3COO− as an electron donor. Mossbauer investigations of solid phase samples obtained during the process of the bacterium growth were carried out at room temperature, 77.8 K, 4.2 K without and with the presence of an external magnetic field (6 T) applied perpendicular to the γ‐bebam.

Reduction of synthetic ferrihydrite by a binary anaerobic culture of Anaerobacillus alkalilacustris and Geoalkalibacter ferrihydriticus grown on mannitol at pH 9.5

In the course of an investigation of alkaliphilic iron reduction, metabiotic interactions in a binary culture reducing synthetic ferrihydrite (SF) have been studied. The binary culture contained two anaerobic bacteria: the alkaliphilic organotrophic bacillus Anaerobacillus alkalilacustris, which ferments sugars and sugar alcohols and is incapable of iron reduction, and the dissimilatory iron-reducing bacterium Geoalkalibacter ferrihydriticus, which is able to grow on acetate at the expense of anaerobic respiration. The experiments were performed under conditions of SF excess and deficiency. It was expected that G. ferrihydriticus would oxidize the acetate formed in the course of mannitol fermentation by A. alkalilacustris. The results were different from the expected ones: in the binary culture, fermentation products other than acetate were used for iron reduction; these were primarily formate and ethanol, which led to acetate accumulation rather than consumption. The reduction of SF to magnetite and/or siderite followed the earlier established regularities. The preferential order of donor utilization by G. ferrihydriticus did not conform to the energy yields of the corresponding reactions. Thus, it has been shown that there may be interactions in microbial communities that cannot be predicted from the characteristics of pure cultures. The degradation pathways of organic matter in communities may differ considerably from those observed in pure cultures, even in pure cultures of highly specialized organisms.

Mössbauer study of layered iron hydroxysulfides: Tochilinite and valleriite

Natural and synthetic layered iron hydroxysulfides: tochilinite and valleriite, have been investigated by Mössbauer spectroscopy. Tochilinite, magnetite, troilite, and pyrite phases were found in the products of tochilinite synthesis under different conditions. The relative contents of the phases found are determined as functions of the relative magnesium content in the initial mixture. Crystallochemical identification of the 57Fe subspectra of valleriite has been performed.

Mössbauer study of formation of iron oxides and carbonate by dissimilatory alkaliphilic bacterium

The process of amorphous Fe(III)-hydroxide (AFH) reduction by anaerobic alkaliphilic bacterium – Geoalkalibacter ferrihydriticus (strain Z-0531) was investigated by Mossbauer spectroscopy methods. Strain Z-0531 was isolated from the sediments of soda Lake Khadyn (Tuva, Russian Federation). The influence of AFH concentration and the concentration of anthraquinone-2,6-disulfonate added to the cultivation medium as well as the incubation time influence on the reducing process were studied. It was found that increase in the time of cultivation of bacteria led to an increase in the relative content of phases containing ferrous atoms that could be explained by the adaptation of bacterium to the cultivation medium.

Mössbauer study of compounds of Cu3 − xFexSnS4 and Cu2Fe1 −xZnxSnS4 systems

A Mössbauer study of the structural and charge states of 57Fe and 119Sn atoms in the compounds of Cu3 −xFexSnS4 and Cu2Fe1 − xZnxSnS4 systems was performed. It was shown that the iron atoms in the compounds of both systems were in the divalent and trivalent states occupying the tetrahedral positions of the structure. The character of the changes of the degree of covalency of the Fe2+-S, Fe3+-S and Sn4+-S bonds during the isomorphic substitution in the systems was established.

Mössbauer Investigation of Biologically-Induced Mineralization Processes

Mossbauer investigations of the kinetics of iron-containing mineral formation in controlled conditions by thermophilic Fe(III)-reducing bacteria were carried out. Anaerobic bacterium (strain Z-0001) was isolated from the ferric sediments of hot springs Stolbovskie, Kunashir Island. This microorganism used the amorphous Fe(III)-oxide as an electron acceptor and acetate CH3COO− as an electron donor. Probes of solid phase processed by bacteria were sampled at different time intervals for the cultures incubated with 20 and 100% of CO2 in gas phase and studied by Mossbauer spectroscopy. The influence of physical and chemical conditions on the mineral phase formation was also investigated.

Mössbauer and Magnetic Study of Solid Phases Formed by Dissimilatory Iron-Reducing Bacteria

Mössbauer investigations of solid phases that were formed during the reduction of amorphous synthesized ferrihydrite (SF) by thermophilic anaerobic iron-reducing bacterium Thermincola ferriacetica (strain Z-0001) and alkaliphilic anaerobic iron-reducing bacterium Geoalkalibacter ferrihydriticus (strain Z-0531) were carried out at room, liquid nitrogen and helium temperatures in the presence or the absence of an external magnetic field (6 T). The magnetization M (T, H) was measured in the temperature interval 80-300 K and magnetic field up to 10 kOe. It was performed zero field cooling (ZFC) and field cooling (FC) measurements of M (T).

Mössbauer study of isomorphous substitutions in Cu2Fe1-xCuxSnS4 and Cu2Fe1-xZnxSnS4 series

The investigation of isomorphous substitutions in minerals of stannite group was carried out for two series Cu2FeSnS4 – Cu3SnS4 (stannite – kuramite) and Cu2FeSnS4 – Cu2ZnSnS4 (stannite – kesterite) by 57Fe and 119Sn Mossbauer spectroscopy. The calculation of the lattice contribution to the electric field gradient tensor at the 57Fe nuclei and an estimation of the quadrupole shift for the determination of Fe3+ atom positions in the structure were carried out. The charge and structural states of Fe and Sn atoms in compounds of the two systems were determined. The schemes of isomorphous substitutions were found for both series in all range of iron concentrations. The changes in the covalence degree of the bonds Fe2+ − S, Fe3+ − S and Sn4+ − S in the process of the substitution were found.

EMR Spectra of Iron-Based Nanoparticles Produced by Dissimilatory Bacteria

We have studied electron magnetic resonance spectra of iron-oxide nanoparticles related to iron reduction metabolism of dissimilatory bacterium Thermincola ferriacetica. It is found that the resonance parameters of metabolic products change notably with time. The X-ray diffraction data indicates partial crystallization of iron oxide during long time storage under air open conditions.

Mössbauer Study of Iron Minerals Formed by Dissimilatory Bacterium

The kinetics of formation of iron-containing minerals by thermophilic dissimilatory iron-reducing bacteria Themincola ferriacetica (strain Z-0001) has been investigated by Mössbauer spectroscopy. The Mossbauer measurements were performed at room and low (77 and 4.2 K) temperatures and in a magnetic field of 6 T. Electron magnetic resonance (EМR) measurements were also carried out.