Iron or sulfur respiration-an adaptive choice determining the fitness of a natronophilic bacterium Dethiobacter alkaliphilus in geochemically contrasting environments

Haloalkaliphilic microorganisms are double extremophiles functioning optimally at high salinity and pH. Their typical habitats are soda lakes, geologically ancient yet widespread ecosystems supposed to harbor relict microbial communities. We compared metabolic features and their determinants in two strains of the natronophilic species Dethiobacter alkaliphilus, the only cultured representative of the class "Dethiobacteria" (Bacillota). The strains of D. alkaliphilus were previously isolated from geographically remote Mongolian and Kenyan soda lakes. The type strain AHT1^T was described as a facultative chemolithoautotrophic sulfidogen reducing or disproportionating sulfur or thiosulfate, while strain Z-1002 was isolated as a chemolithoautotrophic iron reducer. Here, we uncovered the iron reducing ability of strain AHT1^T and the ability of strain Z-1002 for thiosulfate reduction and anaerobic Fe(II) oxidation. Key catabolic processes sustaining the growth of both D. alkaliphilus strains appeared to fit the geochemical settings of two contrasting natural alkaline environments, sulfur-enriched soda lakes and iron-enriched serpentinites. This hypothesis was supported by a meta-analysis of Dethiobacterial genomes and by the enrichment of a novel phylotype from a subsurface alkaline aquifer under Fe(III)-reducing conditions. Genome analysis revealed multiheme c-type cytochromes to be the most probable determinants of iron and sulfur redox transformations in D. alkaliphilus. Phylogeny reconstruction showed that all the respiratory processes in this organism are likely provided by evolutionarily related early forms of unconventional octaheme tetrathionate and sulfite reductases and their structural analogs, OmhA/OcwA Fe(III)-reductases. Several phylogenetically related determinants of anaerobic Fe(II) oxidation were identified in the Z-1002 genome, and the oxidation process was experimentally demonstrated. Proteomic profiling revealed two distinct sets of multiheme cytochromes upregulated in iron(III)- or thiosulfate-respiring cells and the cytochromes peculiar for Fe(II) oxidizing cells. We suggest that maintaining high variation in multiheme cytochromes is an effective adaptive strategy to occupy geochemically contrasting alkaline environments. We propose that sulfur-enriched soda lakes could be secondary habitats for D. alkaliphilus compared to Fe-rich serpentinites, and that the ongoing evolution of Dethiobacterales could retrace the evolutionary path that may have occurred in prokaryotes at a turning point in the biosphere's history, when the intensification of the sulfur cycle outweighed the global significance of the iron cycle.

Study of Phase Transformations and Hyperfine Interactions in Fe3O4 and Fe3O4@Au Nanoparticles

The paper presents the results of a study of iron oxide nanoparticles obtained by chemical coprecipitation, coated (Fe₃O₄@Au) and not coated (Fe₃O₄) with gold, which were subjected to thermal annealing. To characterize the nanoparticles under study, scanning and transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy on ⁵⁷Fe nuclei were used, the combination of which made it possible to establish a sequence of phase transformations, changes in morphological and structural characteristics, as well as parameters of hyperfine interactions. During the studies, it was found that thermal annealing of nanoparticles leads to phase transformation processes in the following sequence: nonstoichiometric magnetite (Fe_3-γO₄) → maghemite (γ-Fe₂O₃) → hematite (α-Fe₂O₃), followed by structural ordering and coarsening of nanoparticles. It is shown that nanoparticles of nonstoichiometric magnetite with and without gold coating are in the superparamagnetic state with a slow relaxation rate. The magnetic anisotropy energy of nonstoichiometric magnetite is determined as a function of the annealing temperature. An estimate was made of the average size of the region of magnetic ordering of Fe atoms in nonstoichiometric magnetite, which is in good agreement with the data on the average sizes of nanoparticles determined by scanning electron microscopy.

Peculiar Spin-Crossover Behavior in the 2D Polymer K[FeIII(5Cl-thsa)2]

A potassium salt of the N₂S₂O₂-coordination Fe(III) anion K[Fe(5Cl-thsa)₂] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K⁺ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K⁺ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T_1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to ⁵⁷Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (Δγ_HS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P2₁/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, ⁵⁷Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.

Study of Magnetic Properties of Fe100-xNix Nanostructures Using the Mössbauer Spectroscopy Method

Hyperfine interactions of 57Fe nuclei in Fe100-xNix nanostructures synthesized in polymer ion-track membranes were studied by Mössbauer spectroscopy. The main part of obtained nanostructures was Fe100-xNix nanotubes with bcc structure for 0 ≤ x ≤ 40, and with fcc structure for 50 ≤ x ≤ 90. The length, outside diameter and wall thickness of nanotubes were 12 μm, 400 ± 10 nm and 120 ± 5 nm respectively. For the studied nanotubes a magnetic texture is observedalong their axis. The average value of the angle between the direction of the Fe atom magnetic moment and the nanotubes axis decreases with increasing of Ni concentration for nanotubes with bcc structure from ~50° to ~40°, and with fcc structure from ~55° to ~46°. The concentration dependences of the hyperfine parameters of nanotubes Mössbauer spectra are qualitatively consistent with the data for bulk polycrystalline samples. With Ni concentration increasing the average value of the hyperfine magnetic field increases from ~328 kOe to ~335 kOe for the bcc structure and drops to ~303 kOe in the transition to the fcc structure and then decreases to ~290 kOe at x = 90. Replacing the Fe atom with the Ni atom in the nearest environment of Fe atom within nanotubes with bcc structure lead to an increase in the hyperfine magnetic field by "6-9 kOe", and in tubes with fcc structure-to a decrease in the hyperfine magnetic field by "11-16 kOe". The changes of the quadrupole shift and hyperfine magnetic field are linearly correlated with the coefficient -(15 ± 5)·10-4 mm/s/kOe.

Genomic Insights Into Energy Metabolism of Carboxydocella thermautotrophica Coupling Hydrogenogenic CO Oxidation With the Reduction of Fe(III) Minerals

The genus Carboxydocella forms a deeply branching family in the class Clostridia and is currently represented by three physiologically diverse species of thermophilic prokaryotes. The type strain of the type species, Carboxydocella thermautotrophica 41T, is an obligate chemolithoautotroph growing exclusively by hydrogenogenic CO oxidation. Another strain, isolated from a hot spring at Uzon caldera, Kamchatka in the course of this work, is capable of coupling carboxydotrophy and dissimilatory reduction of Fe(III) from oxic and phyllosilicate minerals. The processes of carboxydotrophy and Fe(III) reduction appeared to be interdependent in this strain. The genomes of both isolates were sequenced, assembled into single chromosome sequences (for strain 41T a plasmid sequence was also assembled) and analyzed. Genome analysis revealed that each of the two strains possessed six genes encoding diverse Ni,Fe-containing CO dehydrogenases (maximum reported in complete prokaryotic genomes), indicating crucial role of carbon monoxide in C. thermautotrophica metabolism. Both strains possessed a set of 30 multiheme c-type cytochromes, but only the newly isolated Fe-reducing strain 019 had one extra gene of a 17-heme cytochrome, which is proposed to represent a novel determinant of dissimilatory iron reduction in prokaryotes. Mössbauer studies revealed that strain 019 induced reductive transformation of the abundant ferric/ferrous-mica mineral glauconite to siderite during carboxydotrophic growth. Reconstruction of the C. thermautotrophica strains energy metabolism is the first comprehensive genome analysis of a representative of the deep phylogenetic branch Clostridia Incertae Sedis, family V. Our data provide insights into energy metabolism of C. thermautotrophica with an emphasis on its ecological implications.

Towards a revisitation of vesuvianite-group nomenclature: the crystal structure of Ti-rich vesuvianite from Alchuri, Shigar Valley, Pakistan

Vesuvianite containing 5.85 wt% TiO₂ from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been investigated by means of electron microprobe analyses, gas-chromatographic analysis of H₂O, X-ray powder diffraction, single-crystal X-ray structure refinement, ²⁷Al NMR, ⁵⁷Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are: a = 15.5326 (2), c = 11.8040 (2) Å, space group P4/nnc. The structure was refined to final R₁ = 0.031, wR₂ = 0.057 for 11247 I > 2σ(I). A general crystal-chemical formula of studied sample can be written as follows (Z = 2): ^[8-9](Ca_17.1Na_0.9) ^[8]Ca_1.0^[5](Fe²⁺_0.44Fe³⁺_0.34Mg_0.22) ^[6](Al_3.59Mg_0.41) ^[6](Al_4.03Ti_2.20Fe³⁺_1.37Fe²⁺_0.40) (Si₁₈O₆₈) [(OH)_5.84O_2.83F_1.33]. The octahedral site Y2 is Al-dominant and does not contain transition elements. Another octahedral site Y3 is also Al-dominant and contains Fe²⁺, Fe³⁺ and Ti. The site Y1 is split into Y1a and Y1b predominantly occupied by Fe²⁺ and Fe³⁺, respectively. The role of the Y1 site in the diversity of vesuvianite-group minerals is discussed.

Thermal stabilization of phase and structural state in binary lamellar metallic systems

The paper proposes and describes a physical model of thermally induced processes in binary lamellar systems. The model has been developed for the theoretical explanation of an experimentally revealed fact of thermal stabilization of intermetallic phases on the surface of a lamellar sample. Based on the model we developed an algorithm for calculations and a computer code that operates with three one-phase and two two-phase regions in the binary alloy state diagram. The computational model includes as inputs changes in concentration boundaries for existing phases with change in temperature, as well as arbitrary temperature-time regimes for the thermal treatment of the lamellar system under investigation. Good agreement between the theoretical calculations and Mössbauer investigations of binary lamellar Fe-Be systems has been achieved.

[High-temperature microbial sulfate reduction can be accompanied by magnetite formation]

The hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus was found to be capable of lithoautotrophic growth on medium containing molecular hydrogen, sulfate, and amorphous Fe(III) oxide. During the growth of this microorganism, amorphous Fe(III) oxide was transformed into black strongly magnetic sediment rich in magnetite, as shown by Mossbauer studies. Experiments involving inhibition of microbial sulfate reduction and abiotic controls revealed that magnetite production resulted from chemical reactions proceeding at elevated temperatures (83 degrees C) between molecular hydrogen, amorphous Fe(III) oxide, and sulfide formed enzymatically in the course of dissimilatory sulfate reduction. It follows that magnetite production in this system can be characterized as biologically mediated mineralization. This is the first report of magnetite formation as a result of activity of sulfate-reducing microorganisms.