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Microbial electrosynthesis system (MES) is a promising method that can use carbon dioxide, which is a greenhouse gas, to produce methane which acts as an energy source, without using organic substances. However, this bioelectrical reduction reaction can proceed at a certain high applied voltage when coupled with water oxidation in the anode coated with metallic catalyst. When coupled with the oxidation of HS– to SO 4 2−, methane production is thermodynamically more feasible, thus implying its production at a considerably lower applied voltage. In this study, we demonstrated the possibility of electrotrophic methane production coupled with HS– oxidation in a cost-effective bioanode chamber in the MES without organic substrates at a low applied voltage of 0.2 V. In addition, microbial community analyses of biomass enriched in the bioanode and biocathode were used to reveal the most probable pathway for methane production from HS– oxidation. In the bioanode, electroautotrophic SO 4 2− production accompanied with electron donation to the electrode is performed mainly by the following two steps: first, incomplete sulfide oxidation to sulfur cycle intermediates (SCI) is performed; then the produced SCI are disproportionated to HS– and SO 4 2−. In the biocathode, methane is produced mainly via H 2 and acetate by electron-accepting syntrophic bacteria, homoacetogens, and acetoclastic archaea. Here, a new eco-friendly MES with biological H 2 S removal is established. [Display omitted]. [ABSTRACT FROM AUTHOR]

Chemolithoautotrophic Campylobacterota are widespread and predominant in worldwide hydrothermal vents, and they are key players in the turnover of zero-valence sulfur. However, at present, the mechanism of cyclooctasulfur activation and catabolism in Campylobacterota bacteria is not clearly understood. Here, we investigated these processes in a hydrothermal vent isolate named Sulfurovum indicum ST-419. A transcriptome analysis revealed that multiple genes related to biofilm formation were highly expressed during both sulfur oxidation and reduction. Additionally, biofilms containing cells and EPS coated on sulfur particles were observed by SEM, suggesting that biofilm formation may be involved in S0 activation in Sulfurovum species. Meanwhile, several genes encoding the outer membrane proteins of OprD family were also highly expressed, and among them, gene IMZ28_RS00565 exhibited significantly high expressions by 2.53- and 7.63-fold changes under both conditions, respectively, which may play a role in sulfur uptake. However, other mechanisms could be involved in sulfur activation and uptake, as experiments with dialysis bags showed that direct contact between cells and sulfur particles was not mandatory for sulfur reduction activity, whereas cell growth via sulfur oxidation did require direct contact. This indirect reaction could be ascribed to the role of H2S and/or other thiol-containing compounds, such as cysteine and GSH, which could be produced in the culture medium during sulfur reduction. In the periplasm, the sulfur-oxidation-multienzyme complexes soxABXY1Z1 and soxCDY2Z2 are likely responsible for thiosulfate oxidation and S0 oxidation, respectively. In addition, among the four psr gene clusters encoding polysulfide reductases, only psrA3B3C3 was significantly upregulated under the sulfur reduction condition, implying its essential role in sulfur reduction. These results expand our understanding of the interactions of Campylobacterota with the zero-valence sulfur and their adaptability to deep-sea hydrothermal environments. [ABSTRACT FROM AUTHOR]

Low atomicity clusters present properties dependent on the size, due to the quantum confinement, with well‐defined electronic structures and high stability. Here it is shown that Ag5 clusters catalyze the complete oxidation of sulfur to S+6. Ag5 catalytic activity increases with different oxidant species in the order O2 ≪ H2O2 < OH•. Selective oxidation of thiols on the cysteine residues of glutathione and thioredoxin is the primary mechanism human cells have to maintain redox homeostasis. Contingent upon oxidant concentration, Ag5 catalyzes the irreversible oxidation of glutathione and thioredoxin, triggering apoptosis. Modification of the intracellular environment to a more oxidized state to mimic conditions within cancer cells through the expression of an activated oncogene (HRASG12V) or through ARID1A mutation, sensitizes cells to Ag5 mediated apoptosis. While cancers evolve to evade treatments designed to target pathways or genetic mutations that drive them, they cannot evade a treatment that takes advantage of aberrant redox homeostasis, which is essential for tumor progression and metastasis. Ag5 has antitumor activity in mice with orthotopic lung tumors reducing primary tumor size, and the burden of affected lymphatic nodes. The findings suggest the unique intracellular redox chemistry of Ag5 may lead to new redox‐based approaches to cancer therapy. [ABSTRACT FROM AUTHOR]

Methane is produced in a microbial electrosynthesis system (MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions. In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS− oxidized to SO 4 2− at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H 2 was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea , and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H 2 was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion, the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens, including Methanobacterium and Methanolinea, produced methane via H 2. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxidative weathering of pyrite plays an important role in the biogeochemical cycling of Fe and S in terrestrial environments. While the mechanism and occurrence of biologically accelerated pyrite oxidation under acidic conditions are well established, much less is known about microbially mediated pyrite oxidation at circumneutral pH. Recent work (Percak‐Dennett et al., 2017, Geobiology, 15, 690) has demonstrated the ability of aerobic chemolithotrophic microorganisms to accelerate pyrite oxidation at circumneutral pH and proposed two mechanistic models by which this phenomenon might occur. Here, we assess the potential relevance of aerobic microbially catalyzed circumneutral pH pyrite oxidation in relation to subsurface shale weathering at Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) in Pennsylvania, USA. Specimen pyrite mixed with native shale was incubated in groundwater for 3 months at the inferred depth of in situ pyrite oxidation. The colonized materials were used as an inoculum for pyrite‐oxidizing enrichment cultures. Microbial activity accelerated the release of sulfate across all conditions. 16S rRNA gene sequencing and metagenomic analysis revealed the dominance of a putative chemolithoautotrophic sulfur‐oxidizing bacterium from the genus Thiobacillus in the enrichment cultures. Previously proposed models for aerobic microbial pyrite oxidation were assessed in terms of physical constraints, enrichment culture geochemistry, and metagenomic analysis. Although we conclude that subsurface pyrite oxidation at SSCHZO is largely abiotic, this work nonetheless yields new insight into the potential pathways by which aerobic microorganisms may accelerate pyrite oxidation at circumneutral pH. We propose a new "direct sulfur oxidation" pathway, whereby sulfhydryl‐bearing outer membrane proteins mediate oxidation of pyrite surfaces through a persulfide intermediate, analogous to previously proposed mechanisms for direct microbial oxidation of elemental sulfur. The action of this and other direct microbial pyrite oxidation pathways have major implications for controls on pyrite weathering rates in circumneutral pH sedimentary environments where pore throat sizes permit widespread access of microorganisms to pyrite surfaces. [ABSTRACT FROM AUTHOR]

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[Display omitted] • Six oxo-Re(V) complexes containing Salophen ligands, which are different groups on the N -aryl backbone and phenolate arms, were prepared for oxidation to sulfoxides of sulfur compounds using t BuOOH as the oxidizing agent. • A simple and efficient method for sulfur oxidation with excellent yield and high chemoselectivity was developed. • This methodology has remarkable advantages, such as low catalyst loading, fast reaction times, clean reactions, and catalyst stability towards air and moisture. • A general mechanism was proposed for the oxo-Re(V)-catalyzed oxidation reaction of sulfur compounds with t BuOOH as the oxidant. • To elucidate the intrinsic mechanism of the sulfoxidation reaction, the active species that play a major role were investigated. Oxidation, which converts sulfides into sulfoxides, is a widely used method for producing synthetic intermediates in various industries such as chemical, medicinal chemistry, and biology. In this study, we synthesized six oxo-rhenium(V) complexes, ReOClL1-6, using salophen ligands, which are different groups on the N -aryl backbone and phenolate arms, to develop selective and stable oxidation catalysts. Their structures were confirmed using 1H-, 13C- NMR, MALDI-TOF MS, and FTIR. In particular, optimum conditions have been investigated to overcome the synthetic challenge of the direct and selective production of oxidation products such as sulfoxides and/or sulfones. This was achieved with a short reaction time, low catalyst loading, and excellent yields. ReOClL1-6 complexes are active homogeneous catalysts for the oxidation of sulfur compounds (with t BuOOH to sulfoxide). ReOClL4 complex demonstrated superior catalytic performance compared to other complexes, owing to the electronic properties of the ligand scaffold. A general mechanism was proposed for the oxorhenium-catalyzed oxidation reaction of sulfur compounds with t BuOOH as the oxidant. The mechanism includes (i) coordination of t BuOOH to the catalyst, (ii) a homolytic t BuO–OH bond cleavage by oxo-Re(V) complex leads to t BuO and OH radicals, (iii) coordination of OOtBu radicals to the oxo-Re center, formed by OtBu radicals transferring a peroxy H atom in the presence of excess t BuOOH and (iv) a second homolytic bond cleavage of t BuOOORe species by oxo-Re(V) complex leads to t BuO and O 2 − radicals. [ABSTRACT FROM AUTHOR]

The sulfur oxidation on the Ni (1 0 0), (1 1 0) and (1 1 1) surfaces are systematically studied using the first-principles method based density functional theory. It is found that sulfur oxidation is most difficult on the Ni (1 0 0) surface. Surprisingly, the existence of OH can greatly improve the sulfur oxidation on Ni (1 0 0) at 0.25 ML sulfur coverage. A detailed picture on how OH improves sulfur oxidation on Ni (1 0 0) surface is presented, which is helpful to explain how H 2 O can effectively improve the sulfur tolerance of the Ni based SOFC anode catalysts. [ABSTRACT FROM AUTHOR]

Deep-sea vesicomyid clams, including the genus Phreagena, harbor obligate sulfur-oxidizing symbiotic bacteria in gill epithelial cells. Difficulty in maintaining Phreagena clams in rearing tanks has been a major obstacle to achieving a better understanding of their unique biology. To improve the method of rearing Phreagena clams, here we reared them in an artificial chemosynthetic aquarium and evaluated the effects of the aquarium system on long-term clam rearing. We compared the survival of clams reared in the artificial chemosynthetic tank with the survival of those in the normal tank, and analyzed the symbiont abundance using semi-quantification of fluorescent in situ hybridization signals. Our results indicate that the artificial chemosynthetic aquarium system had specific effects on symbiont abundance and possibly on host survival. Furthermore, transmission electron microscopic observations of sulfur globules in the symbiont cells and expression analyses of the dsrA gene of the symbiont indicated that stocked elemental sulfur could be consumed as an energy source to reduce sulfide shortages. We discuss the importance of higher and more stable sulfide concentrations and the proportions of available O and CO in driving appropriate metabolic functions of the symbiont and improving the survival of the clams. [ABSTRACT FROM AUTHOR]

Alkaliphilic sulfur-oxidizing bacteria are highly abundant in naturally occurring soda lakes, where they are found both in surface waters and sediments. Here we studied oxidation of sulfide and thiosulfate in batch cultures of Thioalkalimicrobium aerophilum and Thioalkalivibrio versutus , two species that represent different metabolic types, as indicated by the absence or presence of sulfur production during growth, respectively. With thiosulfate, both species showed the expected sulfur oxidation patterns; however, during growth on sulfide, both T . aerophilum and T . versutus produced sulfur as an intermediate. While T . aerophilum likely uses a Sox-type sulfur oxidation pathway, T . versutus appeared to use a combination of some Sox proteins with heterodisulfide reductase complexes, which is supported by gene expression data. Interestingly, intermediate sulfur production by T . versutus occurred when the sulfur source in the medium had been nearly exhausted, which is unlike what has been described for the well-studied Dsr/Sox pathway in phototrophic sulfur bacteria. Inclusion of some carbon sources (acetate, propionate, fructose) slightly enhanced growth of T . versutus and T . aerophilum in batch cultures, suggesting that carbon co-assimilation may be occurring. Our results indicate that sulfur oxidation processes in alkaliphilic sulfur oxidizers are more complex than previously assumed, and that the enzymes involved warrant further study. [ABSTRACT FROM AUTHOR]

• SMFC was an effective approach to minimize P release to overlying water. • SMFC was conducted to study the effect of S oxidation on P release from sediment. • FeS of sediment was decreased and SO 4 2− of pore water was increased in SMFC group. • Sulfur-oxidizing bacteria were dominant in the SMFC group. • S oxidation process was a neglected contributor to minimizing P release with SMFC. In this study, long-term operation (300 days) of sediment microbial fuel cell (SMFC) was conducted to investigate the effect of sulfur oxidation on phosphorus (P) release from sediment. The result described that the released P to the water column of SMFC group was much lower during the whole operated time, suggesting SMFC was an effective approach to inhibit endogenous P release from sediment. FeS in the sediment was decreased in the vicinity of anode and SO 4 2− concentration was accumulated in the pore water from day 160 onward, suggesting the occurrence of FeS oxidation process. At the same time, part of dissolved Fe2+ was upward-diffused and oxidized to Fe(III) oxides, followed by adsorption P, rendering higher BD-P buildup in the surface sediment (612.50 ± 32.25 μg/g). Further, the potential of sulfur-oxidizing bacteria, Tumebacillus (7.31%) and family Desulfobulbaceae (3.06%), were dominant, confirming bio-sulfur oxidation process in the SMFC group. In conclusion, sulfur oxidation process was a significant contributor to minimize P release from sediment in SMFC. [ABSTRACT FROM AUTHOR]

The oxidation of chemisorbed sulfur on Pt(111) was studied in 0.1 M H 2 SO 4 using combined electrochemical and in situ optical reflectance. The adsorbed sulfur adlayer, prepared by immersion of the Pt electrode in Na 2 S solution, was successively removed by potential cycling between 0.05 and 1.22 V vs. RHE. Correlation of the electrochemical data with the parallel measured changes in optical reflectance provides insight into the intermediate steps of the sulfur oxidation process. In addition to features related to sulfur oxidation and Pt oxide formation and reduction, two transient cathodic current peaks at rather negative potentials (0.19 and 0.41 V) are observed the first cycles, which can be assigned to intermediates of the sulfur oxidation process. The sulfur coverage oxidized in each cycle is initially large but then decreases rapidly, becoming negligibly small after about 10 cycles. Furthermore, a nonlinear change of the reflectance with decreasing sulfur coverage is observed, which suggests changes in the nature of the S-Pt bond with coverage. [ABSTRACT FROM AUTHOR]

Penicillins, as bactericidal antibiotics, have been widely used to treat infections for several decades. Their structure contains both aromatic and thioether moieties susceptible to free radical oxidation. The•OH induced oxidation mechanism of amoxicillin was investigated by pulse radiolysis techniques and by final product analysis performed after steady-state γ-irradiation. The predominant sites of the•OH attack are suggested to be the thioether group, initially yielding an•OH adduct to the sulfur, and the aromatic ring. This adduct to the sulfur converts to sulfur radical cation, which has three competitive reaction paths: (1) by deprotonation at the adjacent carbonα-(alkylthio)alkyl radicals form, which undergo disproportionation leading presumably to sulfoxide as main product; (2) via the pseudo-Kolbe mechanism it may transform toα-aminoalkyl radicals; (3) the radical cation can be stabilized through intramolecular S.˙.O bond formation. The reaction mechanism suggests the presence of a short-living and a stabilized (via hydrogen bonding) long-living•OH adduct to the sulfur. The three-electron bonded dimers of amoxicillin were not formed owing to steric hindrance. Thiyl radicals were also present in equilibrium withα-aminoalkyl radicals. In the presence of dissolved oxygen, aromatic ring hydroxylation occurred along with complex reactions resulting in e.g. oxidation of the methyl groups. The formation of the sulfoxide is especially effective in the presence of dissolved oxygen, under anaerobic condition, however, it is also generated owing to H2O2andα-(alkylthio)alkyl radicals. The thioether moiety appears to be more sensitive to oxidation compared to the aromatic ring in case of amoxicillin. [ABSTRACT FROM AUTHOR]

Little is known about the importance and/or mechanisms of biological mineral oxidation in sediments, partially due to the difficulties associated with culturing mineral-oxidizing microbes. We demonstrate that electrochemical enrichment is a feasible approach for isolation of microbes capable of gaining electrons from insoluble minerals. To this end we constructed sediment microcosms and incubated electrodes at various controlled redox potentials. Negative current production was observed in incubations and increased as redox potential decreased (tested -50 to -400mV vs. Ag/AgCl). Electrode-associated biomass responded to the addition of nitrate and ferric iron as terminal electron acceptors in secondary sediment-free enrichments. Elemental sulfur, elemental iron and amorphous iron sulfide enrichments derived from electrode biomass demonstrated products indicative of sulfur or iron oxidation. The microbes isolated from these enrichments belong to the genera Halomonas, Idiomarina, Marinobacter, and Pseudomonas of the Gammaproteobacteria, and Thalassospira and Thioclava from the Alphaproteobacteria. Chronoamperometry data demonstrates sustained electrode oxidation from these isolates in the absence of alternate electron sources. Cyclic voltammetry demonstrated the variability in dominant electron transfer modes or interactions with electrodes (i.e., biofilm, planktonic or mediator facilitated) and the wide range of midpoint potentials observed for each microbe (from 8 to -295mV vs. Ag/AgCl). The diversity of extracellular electron transfer mechanisms observed in one sediment and one redox condition, illustrates the potential importance and abundance of these interactions. This approach has promise for increasing our understanding the extent and diversity of microbe mineral interactions, as well as increasing the repository of microbes available for electrochemical applications. [ABSTRACT FROM AUTHOR]

Here, we report a type strain AST-10 representing a novel species Sulfurimonas hongkongensis within Epsilonproteobacteria, which is involved in marine sedimentary sulfur oxidation and denitrification. Strain AST-10 (= DSM 22096 = JCM 18418) was isolated from the coastal sediment at the Kai Tak Approach Channel connected to Victoria Harbour in Hong Kong. It grew chemolithoautotrophically using thiosulfate, sulfide or hydrogen as the sole electron donor and nitrate as the electron acceptor under anoxic conditions. It was rod-shaped and grew at 15-35°C (optimum at 30°C), pH 6.5-8.5 (optimum at 7.0-7.5), and 10-60 g L NaCl (optimum at 30 g L). Genome sequencing and annotation of strain AST-10 showed a 2,302,023 bp genome size, with 34.9% GC content, 2,290 protein-coding genes, and 42 RNA genes, including 3 rRNA genes. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT studies on hydroperoxide oxidation of sulfur species. • Mechanistic pathways were modelled and interpreted. • Pathways modelled here provide a substantial library for the improvement of current chemical kinetic models. Density Functional Theory calculations (DFT) are reported on the reactions of hydroperoxides with different classes of sulfur: thiols (RSH), sulfides (RSR) and disulfides (RSSR), all of which are important trace species in the auto-oxidation of jet fuel. It is shown that thiols can react under auto-oxidation conditions with hydroperoxides to form sulfonic acids and alcohols. In contrast, it is shown that disulfide species are more likely to form thiyl radicals, which are less likely to be important for the direct autoxidation of fuels due to prohibitive reaction barriers. The reaction mechanisms reported here for sulfur oxidation and the associated calculated thermodynamic data can be used to extend the applicability of current chemical kinetic models for fuel autoxidation, which are currently treated as a single elementary reaction despite the range of sulfur species found in fuels. [ABSTRACT FROM AUTHOR]

Bacteria that oxidize reduced sulfur compounds like H2S often transiently store sulfur in protein membrane-bounded intracellular sulfur globules; intracellular in this case meaning found inside the cell wall. The cultured bacteria that form these globules are primarily phylogenetically classified in the Proteobacteria and are chemotrophic or photoautotrophic. The current model organism is the purple sulfur bacterium Allochromatium vinosum. Research on this bacterium has provided the groundwork for understanding the protein membranes and the sulfur contents of globules. In addition, it has demonstrated the importance of different genes (e.g. sulfur oxidizing, sox) in their formation and in the final oxidation of sulfur in the globules to sulfate (e.g. dissimilatory sulfite reductase, dsr). Pursuing the characteristics of other intracellular sulfur globule-forming bacteria through genomics, transcriptomics and proteomics will eventually lead to a complete picture of their formation and breakdown. There will be commonality to some of the genetic, physiological and morphological characteristics involved in intracellular sulfur globules of different bacteria, but there will likely be some surprises as well. Copyright © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

SoxAX cytochromes are heme-thiolate proteins that play a key role in bacterial thiosulfate oxidation, where they initiate the reaction cycle of a multi-enzyme complex by catalyzing the attachment of sulfur substrates such as thiosulfate to a conserved cysteine present in a carrier protein. SoxAX proteins have a wide phylogenetic distribution and form a family with at least three distinct types of SoxAX protein. The types of SoxAX cytochromes differ in terms of the number of heme groups present in the proteins (there are diheme and triheme versions) as well as in their subunit structure. While two of the SoxAX protein types are heterodimers, the third group contains an additional subunit, SoxK, that stabilizes the complex of the SoxA and SoxX proteins. Crystal structures are available for representatives of the two heterodimeric SoxAX protein types and both of these have shown that the cysteine ligand to the SoxA active site heme carries a modification to a cysteine persulfide that implicates this ligand in catalysis. EPR studies of SoxAX proteins have also revealed a high complexity of heme dependent signals associated with this active site heme; however, the exact mechanism of catalysis is still unclear at present, as is the exact number and types of redox centres involved in the reaction. [ABSTRACT FROM AUTHOR]

Abstract: Three packing materials for sulfur oxidizing denitrification packed bed systems seeded with acclimated anoxic sludge were evaluated. Two porous media were prepared via thermal fusion with sodium bicarbonate as porogen: sulfur fused with powdered (1) calcium carbonate (CaCO3) (SCa) and (2) oyster shell (SCr). Randomly packed sulfur and limestone granules (S+L) media were used as the control. Results revealed that SCr is the most suitable media as it exhibited the highest nitrate removals and lowest nitrite accumulation. It has macrovoidal pores which facilitated microbial attachment. Additionally, SCr had the highest CaCO3 loading per unit volume and highest media dissolution rate which was favorable to avert pH decrease. But due to high denitrification activity, high sulfate levels in SCr may necessitate a post-treatment step prior to effluent discharge. Due to poor biomass attachment, S+L is most sensitive to change in fluid flow condition. As hydraulic retention time is decreased, S+L exhibited intensive and irreversible performance decline. Inferior denitrification performance of SCa was mainly due to low CaCO3 loading per unit volume, low dissolution kinetics and low alkalinity consumption by denitrifiers. Using modified Stover–Kincannon kinetic model, overall performance and denitrification capacities can be arranged as SCr>S+L>SCa. [Copyright &y& Elsevier]

A ruthenium complex [Ru(H2O){Et2NpyS4(O3)2}] · (4) containing sulfinates, sulfenates S-donors, and water as co-ligand has been synthesized from oxidation of hydrazine complex [Ru(N2H4)(Et2NpyS4)] (3) and completely characterized with X-ray structural analysis [Et2Npy [image omitted]= 4-(diethylamino)-2,6-bis[(2-mercaptophenyl)thiomethyl]pyridine(2-)]. Complex 4 exhibits distorted octahedral coordination of the ruthenium center and the d [Ru-Ssulfinates] and d [Ru-Ssulfenates] are almost equivalent. The average d[S-Osulfinate] at 148.0 pm is ca 10 pm longer than the average d [S-Osulfenate] at 138.0 pm. The sulfinates IR(KBr) bands are located in the range 1132-1113 cm-1 as two band sets, ν(SO)asym and ν(SO)sym, whereas the sulfenates show a single absorbance at approximately 882 cm-1. The lower frequency of the ν(SO) stretches of the sulfenates as compared to that of their sulfinate rivals indicates a weaker S-O bond in the sulfenates and is consistent with X-ray crystal structure data (vide infra). Oxidation of the dithiol ligand Et2NpyS4-H2 (1) under the same condition afforded the disulfide, in this case forming a macrocyclic ligand S,S-Et2NpyS4 (2) as is evidenced by an X-ray crystal structure determination. Thus, the oxidation of 3 involves activation of either the oxygen or thiolate by the ruthenium center. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation of finely ground (−200μm) bornite (Cu5FeS4) by Acidithiobacillus ferrooxidans was evaluated in oxygen uptake and shake flasks experiments. The oxidation was a net acid-consuming reaction. Residual bornite was not detected by X-fray diffraction in solids after 2 days of contact in acid leach solution, indicating that the chemical and biological oxidation of bornite was relatively fast. Virtually 100% of copper solubilization was achieved in A. ferrooxidans cultures with or without ferrous iron, while in abiotic controls the copper extraction was around 30%. Bornite was not oxidized by Acidithiobacillus thiooxidans in respirometric or shake flasks experiments. Covellite (CuS) was detected as a secondary phase under all experimental conditions. Sulfur and jarosite were formed only in the presence of A. ferrooxidans. [Copyright &y& Elsevier]

Abstract: Mesophilic iron and sulfur-oxidizing acidophiles are readily found in acid mine drainage sites and bioleaching operations, but relatively little is known about their activities at suboptimal temperatures and in cold environments. The purpose of this work was to characterize the oxidation of elemental sulfur (S0), tetrathionate (S4O6 2−) and ferrous iron (Fe2+) by the psychrotolerant Acidithiobacillus strain SS3. The rates of elemental sulfur and tetrathionate oxidation had temperature optima of 20° and 25°C, respectively, determined using a temperature gradient incubator that involved narrow (1.1°C) incremental increases from 5° to 30°C. Activation energies calculated from the Arrhenius plots were 61 and 89kJmol−1 for tetrathionate and 110kJmol−1 for S0 oxidation. The oxidation of elemental sulfur produced sulfuric acid at 5°C and decreased the pH to approximately 1. The low pH inhibited further oxidation of the substrate. In media with both S0 and Fe2+, oxidation of elemental sulfur did not commence until all available ferrous iron was oxidized. These data on sequential oxidation of the two substrates are in keeping with upregulation and downregulation of several proteins previously noted in the literature. Ferric iron was reduced to Fe2+ in parallel with elemental sulfur oxidation, indicating the presence of a sulfur:ferric iron reductase system in this bacterium. [Copyright &y& Elsevier]

Abstract: The central protein of the sulfur-oxidizing enzyme system of Paracoccus pantotrophus, SoxYZ, reacts with three different Sox proteins. Its active site Cys110Y is on the carboxy-terminus of the SoxY subunit. SoxYZ “as isolated” consisted mainly of the catalytically inactive SoxY-Y(Z)2 heterotetramer linked by a Cys110Y-Cys110Y interprotein disulfide. Sulfide activated SoxYZ “as isolated” 456-fold, reduced the disulfide, and yielded an active SoxYZ heterodimer. The reductant tris(2-carboxyethyl)phosphine (TCEP) inactivated SoxYZ. This form was not re-activated by sulfide, which identified it as a different inactive form. In analytical gel filtration, the elution of “TCEP-treated” SoxYZ was retarded compared to active SoxYZ, indicating a conformational change. The possible enzymes involved in the re-activation of each inactive form of SoxYZ are discussed. [Copyright &y& Elsevier]

The article discusses a study which isolated and characterized the Acidithiobacillus ferrooxidants strain D3-2, which has a high copper bioleaching activity, from a copper mine in Chile. It is indicated that the sulfite oxidase of strain D3-2 was much more resistant to sulfite ion than that of ATCC 23270. It is confirmed that the strain D3-2 ables to solubilize copper from chalcopyrite than strain ATCC 23270, with a sulfite-sensitive sulfite oxidase.

The article discusses the purification of sulfide:quinone oxidoreductase (SQR) from the acidophilic iron-oxidizing bacterium, Acidithiobacillus ferrooxidans, grown on sulfur medium. Western blotting analysis revealed an increased level of SQR synthesis in the A. ferroxidans NASF-1 cells, grown on sulfur medium. This implied the involvement of SQR in elemental sulfur oxidation in the sulfur-grown A. ferrooxidans NASF-1 cells.

Abstract: It is known that methylthio-s-triazines can be transformed to the corresponding 2-hydroxy derivatives through sulfoxides and sulfones in aerobic and flooded soil; however, production of sulfoxides and/or sulfones from methylthio-s-triazines by isolated s-triazine-degrading bacteria has not been reported yet. In the present study, a new bacterial strain, JUN7, was obtained from Japanese soil; the bacterium is capable of transforming simetryn to 2-methylsulfinyl 4,6-bis(ethylamino)-s-triazine (sulfoxide simetryn) and 2-hydroxy-4,6-bis(ethylamino)-s-triazine (2-hydroxy simetryn) in a Luria-Bertani (LB) medium. This is the first isolation of the specific microorganism that mediates sulfur oxidation of methylthio-s-triazines, as far as we know. Strain JUN7 could decrease other methylthio-s-triazines such as dimethametryn and prometryn, but not chlorinated s-triazines (atrazine, simazine, and terbuthylazine) and methoxy-s-triazine (atraton) in 1/10 LB medium. Strain JUN7 did not possessed gene atzA or trzN encoding triazine-degrading enzymes, suggesting that the strain may have another metabolic system. Characterizations of strain JUN7 based on comparative morphology, physiological classification, and comparison of the partial 16S rRNA sequence indicated that it is assigned as a Bacillus cereus species. [Copyright &y& Elsevier]

Thermo-acidophilic prokaryotes isolated from geothermal sites in Yellowstone National Park were identified as novel α- Proteobacteria, distantly related (~93% 16S rRNA gene identity) to the mesophilic acidophile Acidisphaera rubrifaciens. One of these isolates (Y008) was shown to be more thermophilic than all previously characterized acidophilic proteobacteria, with a temperature optimum for growth between 50 and 55°C and a temperature maximum of 65°C. Growth was observed in media maintained at pH between 1.75 and 3.0 and was fastest at pH between 2.5 and 3.0. The G + C content of Y008 was 71.8±0.9 mol%. The acidophile was able to grow heterotrophically on a range of organic substrates, including various monosaccharides, alcohols and amino acids and phenol, though growth on single organic compounds required the provision of one or more growth factors. The isolate oxidized sulfur to sulfuric acid in media containing yeast extract, but was not capable of autotrophic growth with sulfur as energy source. Growth occurred under aerobic conditions and also in the absence of oxygen via anaerobic respiration using ferric iron as terminal electron acceptor. Based on these genotypic and phenotypic traits, it is proposed that Y008 represents the type species of Acidicaldus organivorus, gen. nov., sp. nov. [ABSTRACT FROM AUTHOR]

Abstract: Microbial redox reactions involving inorganic sulfur compounds, mainly the sulfur anions, are one of the vital reactions responsible for the environmental sulfur balance. These reactions are mediated by phylogenetically diverse prokaryotes, some of which also take part in the extraction of metal ions from their sulfur containing ores. These sulfur oxidizers oxidize inorganic sulfur compounds like sulfide, thiosulfate etc. to produce reductants that are used for carbon dioxide fixation or in respiratory electron transfer chains. The sulfur oxidizing gene cluster (sox) of α-Proteobacteria comprises of at least 15 genes, forming two transcriptional units, viz., soxSR and soxVWXYZABCDEFGH. SoxV is known to be a CcdA homolog involved in the transport of reductants from cytoplasm to periplasm. SoxW and SoxS are periplasmic thioredoxins, which (SoxW) interact with SoxV and thereby help in the redox reactions. We have employed homology modeling to construct the three-dimensional structures of the SoxV, SoxW and SoxS proteins from Rhodovulum sulfidophilum. With the help of docking and molecular dynamics simulations we have identified the amino acid residues of these proteins involved in the interaction. The probable biochemical mechanism of the transport of reductants through the interactions of these proteins has also been investigated. Our study provides a rational basis to interpret the molecular mechanism of the biochemistry of sulfur anion oxidation reactions by these ecologically important organisms. [Copyright &y& Elsevier]

Abstract: Microbial oxidation of reduced inorganic sulfur compounds mainly sulfur anions in the environment is one of the major reactions of the global sulfur cycle mediated by phylogenetically diverse prokaryotes. The sulfur oxidizing gene cluster (sox) of α-Proteobacteria comprises of at least 16 genes, which form two transcriptional units, viz., soxSRT and soxVWXYZABCDEFGH. Sequence analysis reveals that soxD gene product (SoxD) belongs to the di-heme cytochrome c family of electron transport proteins whereas soxC gene product (SoxC) is a sulfur dehydrogenase. We employed homology modeling to construct the three-dimensional structures of the SoxC and SoxD from Paracoccus pantotrophus. SoxD protein is known to interact with SoxC. With the help of docking studies we have identified the residues involved in the interaction of SoxC and SoxD. The putative active site geometries of these two proteins as well as the structural basis of the involvements of these proteins in electron transport process during the oxidation of sulfur anions are also investigated. [Copyright &y& Elsevier]

Examines the effects of cyanide, azide, and 2-n-Heptyl-4- hydroxy-quinoline-N-oxide (HQNO) on the oxidation of ferrous ion or elemental sulfur with Acidithiobacillus ferrooxidans NASF-1 cells grown in iron- or sulfur-medium. Indication that iron oxidation of both iron- and sulfur-grown cells was strongly inhibited by cyanide and azide, but not by HQNO; Relative resistance of sulfur oxidation to cyanide and azide; Inhibition of sulfur oxidation by HQNO; Higher sulfide oxidation, ubiquinol dehydrogenase activity, and sulfide:quinone oxidoreductase (SQR) activity in sulfur-grown cells more than in iron-grown cells; Finding that sulfide oxidation in the presence of ubiquinone with the membrane fraction was inhibited by HQNO, but not by cyanide, azide, antimycin A, and myxothiazol; Measurement of the transcription of three genes, encoding an aa3-type cytochrome c oxidase (coxB), a bd-type ubiquinol oxidase (cydA), and an sqr, by real-time reverse transcription polymerase chain reaction; Similarity of transcriptional levels of coxB and cydA genes in sulfur- and iron- grown cells, but that of sqr was 3-fold higher in sulfur-grown cells than in iron-grown cells; Proposed model for the oxidation of reduced inorganic sulfur compounds in A. ferrooxidans NASF-1 cells.

The thermodynamic and kinetic aspects of the oxidation of methanethiol to dimethyl disulfide by oxygen were studied using ab-initio molecular techniques. The reaction was considered as a multi-step process. Geometrical parameters and molecular energies for critical points were determined and characterized at the MP2(Full)/6–31G* level. Afterwards, a study was carried out employing different methods of theoretical model chemistry (G2, G2(MP2), G3 and CBS-4 MB), for which the equilibrium geometry at MP2(Full)/6–31G* was assumed as starting point. The steps governing the rate of the whole reaction were determined and prove to be the same for any level of theory employed. Although the MP2(Full)/6–31G* level is able to afford a good qualitative description of the reaction pathway, the quantitative aspect is less satisfactory. Results from the methods of theoretical model chemistry, on the other hand, accord well with experimental data, if available, and are very useful for studying the thermodynamic and kinetic aspects of chemical reactions. [ABSTRACT FROM AUTHOR]

The thermodynamic and kinetic aspects of the oxidation of methanethiol to dimethyl disulfide by oxygen were studied using ab-initio molecular techniques. The reaction was considered as a multi-step process. Geometrical parameters and molecular energies for critical points were determined and characterized at the MP2(Full)/6–31G* level. Afterwards, a study was carried out employing different methods of theoretical model chemistry (G2, G2(MP2), G3 and CBS-4 MB), for which the equilibrium geometry at MP2(Full)/6–31G* was assumed as starting point. The steps governing the rate of the whole reaction were determined and prove to be the same for any level of theory employed. Although the MP2(Full)/6–31G* level is able to afford a good qualitative description of the reaction pathway, the quantitative aspect is less satisfactory. Results from the methods of theoretical model chemistry, on the other hand, accord well with experimental data, if available, and are very useful for studying the thermodynamic and kinetic aspects of chemical reactions. [ABSTRACT FROM AUTHOR]

Novel methylotrophic Arthrobacter and Hyphomicrobium species are described. Constitutive membrane-associated dimethylsulfone- and dimethylsulfoxide-reductases were found in Arthrobacter methylotrophus strain TGA and Hyphomicrobium sulfonivorans strain S1. Enzyme activities increased during growth with dimethylsulfone or dimethylsulfoxide, respectively, and different ratios of activity with different growth substrates indicated that they are separate enzymes. SDS-PAGE showed some membrane-associated polypeptides to be enhanced during growth with dimethylsulfone (54 kDa in H. sulfonivorans, 21–24 kDa, 54 kDa and 80 kDa in A. methylotrophus). Western blotting with anti-dimethylsulfoxide-reductase antibody showed cross-reaction with 54- and 21-kDa polypeptides in A. methylotrophus. All strains contained rhodanese and sulfur oxygenase after growth with dimethylsulfone. Sulfite was oxidized in the Arthrobacter species by APS reductase and sulfite dehydrogenase. H. sulfonivorans oxidized sulfite with APS reductase, which is unusual for an α-proteobacterium. The Arthrobacter species were distinguished from each other and from other Arthrobacter and Micrococcus species by 16S rRNA gene sequence analysis. The menaquinone and fatty acid profiles of the Arthrobacter species were similar. Their peptidoglycan structures were L-Lys–L-Ser–L-Thr–L-Ala for A. sulfonivorans and L-Lys–L-Ala2–4 for A. methylotrophus. H. sulfonivorans exhibited gross morphology typical for Hyphomicrobium, but possessed helically twisted prosthecae. 16S rRNA gene sequence analysis showed it to be distinct from all the other Hyphomicrobium, Filomicrobium and Pedomicrobium species sequenced to date. Formal descriptions of the new species are given. [ABSTRACT FROM AUTHOR]

Abstract: Microbial redox reactions of inorganic sulfur compounds play a vital role in balancing the turnover of this element in the environment. These vital reactions are carried out by the enzyme system encoded by the sox operon. The central player of the sulfur oxidation biochemistry is the SoxY–Z protein complex. Another protein called SoxF having sulfide dehydrogenase activity has the ability to reactivate the inactivated SoxY–Z protein complex. This SoxF protein is obtained from the sox operon of Chlorobium tepidium. In the present work an attempt has been made to understand the structural details of the activity of SoxF protein. A plausible biochemical mechanism has been predicted regarding the involvement of the SoxF protein in biological sulfur anion oxidation process. Since this is the first report regarding the structural biology of SoxF protein this study may shed light in the hitherto unknown molecular biochemistry of sulfur anion oxidation by sox operon. [Copyright &y& Elsevier]

This genus contains both phototrophs and nonphototrophic members. Here, we present a high-quality complete genome of the strain CHu59-6-5T, isolated from a freshwater sediment. The circular chromosome (4.39 Mbp) of the strain CHu59-6-5T has 64.4% G+C content and contains 4240 genes, of which a total of 3918 genes (92.4%) were functionally assigned to the COG (clusters of orthologous groups) database. Functional genes for denitrification (narGHJI, nirK and qnor) were identified on the genomes of the strain CHu59-6-5T, except for N2O reductase (nos) genes for the final step of denitrification. Genes (soxBXAZY) for encoding sulfur oxidation proteins were identified, and the FSD and soxF genes encoding the monomeric flavoproteins which have sulfide dehydrogenase activities were also detected. Lastly, genes for the assembly of two different RND (resistance-nodulation division) type efflux systems and one ABC (ATP-binding cassette) type efflux system were identified in the Rhodoferax sediminis CHu59-6-5T. Phylogenetic analysis based on 16S rRNA sequences and Average Nucleotide Identities (ANI) support the idea that the strain CHu59-6-5T has a close relationship to the genus Rhodoferax. A polyphasic study was done to establish the taxonomic status of the strain CHu59-6-5T. Based on these data, we proposed that the isolate be classified to the genus Rhodoferax as Rhodoferax sediminis sp. nov. with isolate CHu59-6-5T. [ABSTRACT FROM AUTHOR]

A biofilter packed with immobilized Thiobacillus sp. ST22 was investigated for the treatment of gases containing dimethyl sulfide (DMS). Thiobacillus sp. ST22 was immobilized using a sodium alginate, polyvinyl alcohol and powdered activated carbon as entrapping materials. The experimental results showed that the removal of DMS achieved an efficiency of 99.5%. The optimal spray density and empty bed residence time (EBRT) were and 21 s, respectively. Bacterial communities in the biofilter were assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), which plays a dominant role in the biological processes of simultaneous sulfur oxidation and sulfate reduction. The results showed that Thiobacillus sp. ST22, delta proteobacterium were the predominant bacteria. Dimethyl sulfide can be oxidized into , by Thiobacillus sp. ST22 biooxidation in the outer zones of immobilized cell beads due to aerobic conditions. Dimethyl sulfide can be degradated into , , and HCOOH; can be reduced to , , and by delta proteobacterium and Acidobacteria bacterium using and HCOOH as the electron donors in the inner zones of immobilized cell beads due to anoxic conditions. [ABSTRACT FROM AUTHOR]