Sulfide Production Research Articles

Evaluation of microbial contamination in removable dental prosthesis at different time of usage.

The current study evaluates and compares the percentage distribution of different microorganisms according to their strains and occurrence among the three studied groups. Sample of 30 removable dental prosthesis wearing patients was selected: wearing either complete dentures or partial dentures and without any significant medical history or on prescription medication for the past 3-6 months. Samples were obtained in three subcategories based on the duration of prostheses worn by the patient. A sterile swab made up of cotton moistened with phosphate buffer saline (PBS) was scrubbed on the dental prosthesis at the fitting surfaces and the denture-bearing area of the oral cavity. Within two hours, the collected swab sample was infused in the sterile tube containing 1 ml of 0.84% PBS solution maintained at pH 7-7.2 and sent for microbiological analysis. The samples were then inoculated into different medias. Microbial growth was checked after incubating the culture plates for 48 h at 37°C. Microorganisms were recognized and counted by calibrated colony counter. Gram's stain was used to stain the colony smear and biochemical tests such as coagulase, catalase, oxidase, sugar fermentation with acid and gas production (triple sugar iron), methyl red test, test for indole production, hydrogen sulphide (H2S) production, citrate utilization, urease test, germ tube tests were performed. Descriptive statistics included calculation of means and standard deviation using multivariate analysis. All values were considered statistically significant for a value of P < 0.05. Streptococcus species, Coagulase-negative staphylococcus, Staphylococcus aureus, Candida albicans and Klebsiella pneumoniae showed the maximum positive culture among the secluded microorganisms in all three groups. A progressive increase in the microbial contamination was directly proportional to the duration of removable prosthesis usage.

Structural basis of the inhibition of cystathionine γ-lyase from Toxoplasma gondii by propargylglycine and cysteine.

Cystathionine γ-lyase (CGL) is a PLP-dependent enzyme that catalyzes the last step of the reverse transsulfuration route for endogenous cysteine biosynthesis. The canonical CGL-catalyzed process consists of an α,γ-elimination reaction that breaks down cystathionine into cysteine, α-ketobutyrate, and ammonia. In some species, the enzyme can alternatively use cysteine as a substrate, resulting in the production of hydrogen sulfide (H2 S). Importantly, inhibition of the enzyme and consequently of its H2 S production activity, makes multiresistant bacteria considerably more susceptible to antibiotics. Other organisms, such as Toxoplasma gondii, the causative agent of toxoplasmosis, encode a CGL enzyme (TgCGL) that almost exclusively catalyzes the canonical process, with only minor reactivity to cysteine. Interestingly, the substitution of N360 by a serine (the equivalent amino acid residue in the human enzyme) at the active site changes the specificity of TgCGL for the catalysis of cystathionine, resulting in an enzyme that can cleave both the CγS and the CβS bond of cystathionine. Based on these findings and to deepen the molecular basis underlying the enzyme-substrate specificity, we have elucidated the crystal structures of native TgCGL and the variant TgCGL-N360S from crystals grown in the presence of cystathionine, cysteine, and the inhibitor D,L-propargylglycine (PPG). Our structures reveal the binding mode of each molecule within the catalytic cavity and help explain the inhibitory behavior of cysteine and PPG. A specific inhibitory mechanism of TgCGL by PPG is proposed. This article is protected by copyright. All rights reserved.

Influence of Dieback Disease on Soil Chemistry and Bacterial Diversity in the Rhizosphere of Mango Plants

Influence of dieback disease on the soil chemistry and the morphological, biochemical, and molecular characteristics of bacteria isolated from the rhizosphere of mango plants was studied. The soil samples collected from the rhizosphere of the healthy and dieback-affected mango plants were analyzed for their physicochemical parameters and biochemical characteristics of bacterial isolates. The dieback disease resulted in a significant decrease in pH, water holding capacity, organic matter, total nitrogen content, available phosphorus content, and available potassium content. The number of bacterial isolates showing oxidase production and lactose and sucrose fermentation was increased while the number of those showing urease and hydrogen sulphide production was decreased in the rhizosphere of diseased plants. The genus Bacillus showed maximum prevalence (97%) among the identified genera of rhizobacteria. Eight bacterial species were found to be absent and eight new species appeared in the rhizosphere of diseased plants. The study would be a significant contribution to the literature regarding the dieback mango disease and its relationship with soil composition and its microflora.

Surfactant enhances anaerobic fermentative hydrogen sulfide production: Changes in sulfur-containing organics structure and microbial community

The presence of surfactants in waste activated sludge (WAS) system is generally regarded as beneficial to sludge treatment such as enhancing sludge dewatering and improving value-added fermentation products generation. However, in this study, it was firstly found that sodium dodecylbenzene sulfonate (SDBS, a typical surfactant) obviously increased toxic hydrogen sulfide (H2S) gas production from WAS anaerobic fermentation at environmentally relevant concentrations. Experimental results showed that H2S production from WAS significantly increased from 53.24 × 10−3 to 111.25 × 10−3 mg/g volatile suspended solids (VSS) when SDBS level increased from 0 to 30 mg/g total suspended solid (TSS). It was found that SDBS presence destroyed WAS structure and enhanced sulfur containing organics release. SDBS reduced the proportion of α-helix structure, damaged disulfide bridges and protein conformation, and effectively destroyed protein structure. SDBS promoted sulfur containing organics degradation and provided more readily hydrolyzed micro-molecule organics for sulfide production. Microbial analysis showed that SDBS addition enhanced the abundance of functional genes encoding protease, ATP-binding cassette transporters, and amino acids lyase, enhanced the activities and abundance of hydrolytic microbes, thus increased sulfide production from the hydrolysis of sulfur containing organics. Compared with the control, 30 mg/g TSS SDBS increased organic sulfurs hydrolysis and amino acids degradation by 47.1 % and 63.5 %, respectively. Key genes analysis further showed that SDBS addition promoted sulfate transport system and dissimilatory sulfate reduction. SDBS presence also lowered fermentation pH, promoted the chemical equilibrium transformation of sulfide, thus increased H2S gas release.

Proteome Dynamics of Persulfidation in Leaf Tissue under Light/Dark Conditions and Carbon Deprivation.

Hydrogen sulfide (H2S) acts as a signaling molecule in plants, bacteria, and mammals, regulating various physiological and pathological processes. The molecular mechanism by which hydrogen sulfide exerts its action involves the posttranslational modification of cysteine residues to form a persulfidated thiol motif. This research aimed to study the regulation of protein persulfidation. We used a label-free quantitative approach to measure the protein persulfidation profile in leaves under different growth conditions such as light regimen and carbon deprivation. The proteomic analysis identified a total of 4599 differentially persulfidated proteins, of which 1115 were differentially persulfidated between light and dark conditions. The 544 proteins that were more persulfidated in the dark were analyzed, and showed significant enrichment in functions and pathways related to protein folding and processing in the endoplasmic reticulum. Under light conditions, the persulfidation profile changed, and the number of differentially persulfidated proteins increased up to 913, with the proteasome and ubiquitin-dependent and ubiquitin-independent catabolic processes being the most-affected biological processes. Under carbon starvation conditions, a cluster of 1405 proteins was affected by a reduction in their persulfidation, being involved in metabolic processes that provide primary metabolites to essential energy pathways and including enzymes involved in sulfur assimilation and sulfide production.

Obesogenic diet leads to luminal overproduction of the complex IV inhibitor H2 S and mitochondrial dysfunction in mouse colonocytes.

Obesity is characterized by systemic low-grade inflammation associated with disturbances of intestinal homeostasis and microbiota dysbiosis. Mitochondrial metabolism sustains epithelial homeostasis by providing energy to colonic epithelial cells (CEC) but can be altered by dietary modulations of the luminal environment. Our study aimed at evaluating whether the consumption of an obesogenic diet alters the mitochondrial function of CEC in mice. Mice were fed for 22 weeks with a 58% kcal fat diet (diet-induced obesity [DIO] group) or a 10% kcal fat diet (control diet, CTRL). Colonic crypts were isolated to assess mitochondrial function while colonic content was collected to characterize microbiota and metabolites. DIO mice developed obesity, intestinal hyperpermeability, and increased endotoxemia. Analysis of isolated colonic crypt bioenergetics revealed a mitochondrial dysfunction marked by decreased basal and maximal respirations and lower respiration linked to ATP production in DIO mice. Yet, CEC gene expression of mitochondrial respiration chain complexes and mitochondrial dynamics were not altered in DIO mice. In parallel, DIO mice displayed increased colonic bile acid concentrations, associated with higher abundance of Desulfovibrionaceae. Sulfide concentration was markedly increased in the colon content of DIO mice. Hence, chronic treatment of CTRL mouse colon organoids with sodium sulfide provoked mitochondrial dysfunction similar to that observed in vivo in DIO mice while acute exposure of isolated mitochondria from CEC of CTRL mice to sodium sulfide diminished complex IV activity. Our study provides new insights into colon mitochondrial dysfunction in obesity by revealing that increased sulfide production by DIO-induced dysbiosis impairs complex IV activity in mouse CEC.

Organopolysulfides as high-performance cathode materials for rechargeable aluminum-ion batteries

The development of aluminum-ion batteries (AIBs) is significantly confined by the limited high-performance cathode materials. Herein, organopolysulfides are investigated as active cathode materials to fabricate AIBs. A liquid-phase phenyl tetrasulfide (PTS) can deliver a capacity above 600 mAh g−1 after activation, with the maintenance of 253 mAh g−1 after 100 cycles. Owing to the different S locations, PTS shows several voltage plateaus and an average voltage of ∼0.7 V vs. Al3+/Al with no decay upon cycling. More importantly, the liquid PTS can serve as a high-Coulombic-efficiency cathode (∼99.88% ± 0.57% after stabilization), enlighting the design of high-efficiency and low-resistance conversion-type cathode materials for AIBs. By experimental characterizations accompanied by theoretical calculations, it is found that PTS undergoes stepwise reaction procedures during discharge with final products of Al2S3 and AlCl2-coordinated phenyl sulfide, and partially reforms with elemental S and other organopolysulfides during charge. This study demonstrates new opportunities for the design of high-efficiency conversion-type cathode materials for advanced AIBs.

Transformation of sulfur and nitrogen compounds by sulfidogenic and phototrophic bacteria under the influence of sodium fluoride and potassium bromide

Anthropogenically altered media are characterized by complex pollution, which contains a wide range of organic and inorganic pollutants, including halogen compounds. The influence of halides on transformed ecosystems, in particular, on their sulfidogenic and photosynthetic microbiota and its properties, remains insufficiently studied. The influence of sodium fluoride and potassium bromide at concentrations that are equal and 0.5–4.0 times differed from the maximum permissible concentrations (MPC) (MPC of fluorides and bromides are 0.0789 and 0.0025 mM, respectively) on the reduction of sulfate ions or sulfur (3.47 mM) by sulfidogenic bacteria of Desulfovibrio and Desulfuromonas genera, as well as on the use of thiosulfate or nitrite ions (4.167 mM) as electron donors of anoxygenic photosynthesis by phototrophic purple and green sulfur bacteria of Thiocapsa, Lamprocystis and Chlorobium genera, isolated from the Yavorivske Lake, was investigated. The biomass of bacteria was determined by the turbidimetric method, the content of H2S, SO42-, NО2ˉ and NО3ˉ in the cultural liquid – by the spectrophotometric method, the concentration of S2O32- – by the titrometric method. The intracellular glucose and glycogen content was determined enzymatically in cell-free extracts, using the analytical kit “Diagluc-2”. It was found that sodium fluoride and potassium bromide at concentrations 3.0–4.0 times higher than the MPC repress the biomass accumulation by bacteria Desulfovibrio sp. in the medium with sulfates 2.7−5.8 and 2.1−4.2 times, respectively, and inhibit the hydrogen sulfide production by them 1.8−3.4 and 2.0−3.2 times, respectively. NaF and KBr at concentrations that are equal and 2.0–4.0 times higher than the MPC repress the biomass accumulation by bacteria Desulfuromonas sp. in the medium with sulfur 2.2–6.9 and 2.1–5.6 times, respectively, and at concentrations 3.0–4.0 times higher than the MPC inhibit the hydrogen sulfide production by bacteria 1.9−3.7 and 2.0−2.7 times, respectively. Sodium fluoride and potassium bromide at concentration that 4.0 times exceeded the MPC inhibit the biomass accumulation by bacteria of Thiocapsa, Lamprocystis and Chlorobium genera in the medium with thiosulfates 2.0–2.3 and 1.7–2.0 times, respectively, reduce thiosulfate ions oxidation by them by 31.9–38.5 and 27.1–33.7%, respectively, compared to the control, but stimulate glycogen synthesis by cells of green sulfur bacteria by 106.7 and 64.0%, respectively. NaF and KBr at concentration 4.0 times higher than the MPC inhibit the biomass accumulation by phototrophic bacteria in the medium with nitrites 2.1−2.4 and 1.8−1.9 times, respectively, slow down nitrite ions oxidation by bacteria by 23.5–26.1 and 17.1–20.1%, respectively, compared to the control, but stimulate glycogen synthesis by cells of green sulfur bacteria by 134.7 and 115.0%, respectively. Glycogen content in Chlorobium limicola IMV K-8 cells grown in the media with Na2S2O3 or NaNO2 and NaF at concentration that 4.0 times exceeded the MPC was 81.33 and 84.13 mg/g of dry weight of cells, respectively. Fluoride ions showed a greater toxic effect on bacteria than bromide ions. The resistance of all tested bacteria strains to inorganic pollutants at high concentrations indicates their high biotechnological potential.

When nitrate treatment wins the battle against microbial reservoir souring but loses the war

The injection of seawater into a hydrocarbon reservoir (seawater flooding), as an oil recovery method, triggers microbial reservoir souring, through which microorganisms consume sulfate ions and produce hydrogen sulfide, which is hazardous, corrosive, and detrimental to the environment if enters production wells. A strategy to mitigate this problem is to add nitrate or nitrite to the injection seawater, also known as nitrate or nitrite treatment. This study investigates nitrate treatment in a simulated real-world sector scale hydrocarbon reservoir in the Danish North Sea through a non-isothermal multi-phase multi-component bio-chemical model and field observations. The common expectation is that the higher the concentration of nitrate or nitrite in the injection seawater the less hydrogen sulfide production. However, the results of this study show that slowing down the microorganisms (or mitigation through nitrate treatment) may cause higher hydrogen sulfide production from production wells. Put differently, not only the total amount of hydrogen sulfide generated inside the reservoir matters, but also the location of the generation zone and its distance from production wells matter. Therefore, it is possible that insufficient amounts of nitrate cause the generation zone to move toward the production wells. Hence, more hydrogen sulfide is produced during the lifetime of the reservoir. Moreover, considering laboratory and field scale measurements, in the presence of coupled multi-physics processes, the growth rates at the field scale are significantly lower than those observed in the laboratory experiments, under in-situ conditions, utilizing actual reservoir fluid samples.

Effect of Thallium(I) on Growth, Nutrient Absorption, Photosynthetic Pigments, and Antioxidant Response of Dittrichia Plants.

Dittrichia plants were exposed to thallium (Tl) stress (10, 50, and 100 µM) for 7 days. The Tl toxicity altered the absorption and accumulation of other nutrients. In both the roots and the leaves, there was a decline in K, Mg, and Fe content, but an increase in Ca, Mn, and Zn. Chlorophylls decreased, as did the photosynthetic efficiency, while carotenoids increased. Oxidative stress in the roots was reflected in increased lipid peroxidation. There was more production of superoxide (O2.-), hydrogen peroxide (H2O2), and nitric oxide (NO) in the roots than in the leaves, with increases in both organs in response to Tl toxicity, except for O2.- production in the roots, which fluctuated. There was increased hydrogen sulfide (H2S) production, especially in the leaves. Superoxide dismutase (SOD), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) showed increased activities, except for APX and MDHAR in the roots and GR in the leaves. The components of the ascorbate-glutathione cycle were affected. Thus, ascorbate (AsA) increased, while dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) decreased, except for in the roots at 100 µM Tl, which showed increased GSH. These Tl toxicity-induced alterations modify the AsA/DHA and GSH/GSSG redox status. The NO and H2S interaction may act by activating the antioxidant system. The effects of Tl could be related to its strong affinity for binding with -SH groups, thus altering the functionality of proteins and the cellular redox state.

Reduced sulfide and methane in rising main sewer via calcium peroxide dosing: Insights from microbial physiological characteristics, metabolisms and community traits

Although the biocidal effect of calcium peroxide (CaO2) has attracted increasing attention in wastewater and sludge management, its potential in the reduction of sulfide and methane from sewer is not tapped. This study aims to fill this gap through the long-term operated sewer reactors. Results showed one-time dose of 0.2% (w/v) CaO2 with 12-h exposure decreased the average sulfide and methane production by 80% during one week. The electron paramagnetic resonance and free radical quenching tests indicated free radicals from CaO2 decomposing posed a major contribution on sewer biofilms (•OH>•O2−>alkali). Mechanistic analysis revealed extracellular polymeric matrix breakdown (e.g., protein secondary structure) and cell membrane damage were caused by the increased lipid peroxidation of cells and exacerbated intracellular reactive oxygen species under CaO2 stress. Moreover, the intracellular metabolic pathways, such as electrons provision and transfer, as well as pivotal enzymatic activities (e.g., APS reductase, sulfite reductase and coenzymes F420) were significantly impaired. RT-qPCR analysis unveiled the absolute abundances of dsrA and mcrA were decreased by 7.53–40.37% and 67.00–74.85%, respectively. Although this study broadens the application scope of CaO2 and provides in-depth understanding of advanced oxidation-based technology in sewer management, the pipe scale risk due to the release of calcium ions warrants further investigation.

WCN23-0531 High-fat diet induces kidney damages by decreased hydrogen sulfide production and increased oxidative stress

WCN23-0531 High-fat diet induces kidney damages by decreased hydrogen sulfide production and increased oxidative stress

Reducing sulfide and methane production in gravity sewer sediments through urine separation, collection and intermittent dosing

Sulfide and methane production are a major concern in sewer management. Many solutions with the use of chemicals have been proposed yet incurring huge costs. Here, this study reports an alternative solution to reduce sulfide and methane production in sewer sediments. This is achieved through integration of urine source separation, rapid storage, and intermittent in situ re-dosing into a sewer. Based on a reasonable capacity of urine collection, an intermittent dosing strategy (i.e. 40 min per day) was designed and then experimentally tested using two laboratory sewer sediment reactors. The long-term operation showed that the proposed urine dosing in the experimental reactor effectively reduced sulfidogenic and methanogenic activities by 54% and 83%, compared to those in the control reactor. In-sediment chemical and microbial analyses revealed that the short-term exposure to urine wastewater was effective in suppressing sulfate-reducing bacteria and methanogenic archaea, particularly within a surface active zone of sediments (0–0.5 cm) likely attributed to the biocidal effect of urine free ammonia. Economic and environmental assessments indicated that the proposed urine approach can save 91% in total costs, 80% in energy consumption and 96% in greenhouse gas emissions compared to the conventional use of chemicals (including ferric salt, nitrate, sodium hydroxide, and magnesium hydroxide). These results collectively demonstrated a practical solution without chemical input to improve sewer management.

Panguiarchaeum symbiosum, a potential hyperthermophilic symbiont in the TACK superphylum

The biology of Korarchaeia remains elusive due to the lack of genome representatives. Here, we reconstruct 10 closely related metagenome-assembled genomes from hot spring habitats and place them into a single species, proposed herein as Panguiarchaeum symbiosum. Functional investigation suggests that Panguiarchaeum symbiosum is strictly anaerobic and grows exclusively in thermal habitats by fermenting peptides coupled with sulfide and hydrogen production to dispose of electrons. Due to its inability to biosynthesize archaeal membranes, amino acids, and purines, this species likely exists in a symbiotic lifestyle similar to DPANN archaea. Population metagenomics and metatranscriptomic analyses demonstrated that genes associated with amino acid/peptide uptake and cell attachment exhibited positive selection and were highly expressed, supporting the proposed proteolytic catabolism and symbiotic lifestyle. Our study sheds light on the metabolism, evolution, and potential symbiotic lifestyle of Panguiarchaeum symbiosum, which may be a unique host-dependent archaeon within the TACK superphylum.

Impact of Co-Ensiling of Maize with Moringa oleifera on the Production of Greenhouse Gases and the Characteristics of Fermentation in Ruminants.

The objective of this experiment was to evaluate the impact of maize co-ensiling with increasing percentages of MOL forage on the kinetics of biogas, methane (CH4), carbon monoxide (CO) and hydrogen sulfide (H2S) production, as well as the characteristics of ruminal fermentation and CH4 conversion efficiency, using steers (STI) and sheep (SHI) as inoculum sources. With the STI, the inclusion of MOL reduced (linear: p ≤ 0.0199; quadratic: p ≤ 0.0267) biogas production (mL g-1 DM incubated and degraded), CH4 (mL g-1 DM degraded), CO (mL g-1 DM degraded), and H2S (mL g-1 DM incubated and degraded), without affecting (p > 0.05) the parameters (b = asymptotic gas, c = rate of gas production and Lag = initial delay time before gas production) of CH4 and H2S, and the proportion and production of CH4 per kg of dry matter (DM). In addition, with this inoculum, pH, and dry matter degradation (DMD) increased (linear: p ≤ 0.0060), and although short-chain fatty acids (SCFA) and metabolizable energy (ME) decreased (linear: p < 0.0001; quadratic: p ≤ 0.0015), this did not affect (p > 0.05) the CH4 conversion efficiency. Meanwhile, with the SHI, the inclusion of MOL only decreased (linear: p ≤ 0.0206; quadratic: p ≤ 0.0003) biogas per dry matter (DM) degraded and increased (linear: p ≤ 0.0293; quadratic: p ≤ 0.0325) biogas per DM incubated, as well as the production (mL g-1 DM incubated and degraded and g-1 kg DM) and proportion of CH4, and CO per DM incubated and degraded. In addition, it did not impact (p > 0.05) on the CH4 and H2S parameters, and in the H2S by DM incubated and degraded, and although it increased (linear: p ≤ 0.0292; quadratic: p ≤ 0.0325) the DMD, SCFA, and ME, it was inefficient (quadratic: p ≤ 0.0041) in CH4 conversion. It is concluded that regardless of the percentage of MOL, the STI presented the highest values in the production of biogas, CH4, H2S, DMD, SCFA, and ME, and the lowest pH, so it turned out to be the most efficient in CH4 conversion, while with the SHI only the highest production of CO and pH was obtained, and the lowest DMD, SCFA, and ME, so it was less efficient compared to STI.

Dietary methionine restriction attenuates cognitive dysfunction associated with sleep deprivation by promoting production of hydrogen sulfide, upregulating expression of BDNF and suppressing neuro-inflammation in rats

IntroductionIn this study, we aimed to study the potential role of H2S and the application of dietary methionine restriction (DMR) in the treatment of cognitive dysfunction in sleep deprived rat models.Material and methodsThe rat groups were established as a Control group, a sleep deprivation (SD) group, a SD + NaSH group and a SD + DMR group. Behavioral data was studied via Morris water maze test. TUNEL assay, real-time PCR, immunohistochemistry (IHC) and enzyme-linked immunosorbent assay (ELISA) were performed to study the differences of cognitive impairment related genes and proteins in different rat groups.ResultsPath length and escape latency were higher in the sleep deprived rats compared with the control rats, which were subsequently recovered by the treatment of NaSH or DMR. Also, DMR most significantly recovered the cognitive impairment and neuron status of sleep deprived rats compared with the administration of NaSH. The elevated level of hippocampal Iba1 and H2S production was recovered by NaSH and DMR, and the expressions of hippocampal phenotypic-related genes including NOS, CD68, CD32 and CD206 mRNA also showed similar trend as hippocampal Iba1. Meanwhile, the increased relative expression of IL-6 and IL-4 were recovered by DMR in sleep deprived rats, while the reduced level of hippocampal brain-derived neurotrophic factor (BDNF) and cystathionine γ-lyase (CSE) were elevated by the treatment of NaSH and MDR, with MDR exhibiting the most significant effect.ConclusionsThe application of DMR could attenuate cognitive dysfunction in sleep deprivation rats by upregulating the production of H2S and BDNF expression and alleviating neuro-inflammation responses.

Biofilm formation by sulphate-reducing bacteria on different metals and their prospective role in titanium corrosion

ABSTRACT This study describes the biofilm formation by sulphate-reducing bacteria (SRB) on different materials, which has implications for the biomedical, pharmaceutical, food and chemical process industries. SRB was chosen as a model organism being an anaerobic bacterium. Biofilm formation on different materials and corrosion of titanium by SRB were monitored with time using confocal laser scanning microscopy and fluorescent FISH probes were used to authenticate the SRB strain. The thickness of the mono-culture SRB biofilm has ranged from 4 to 24 µm during thed 12–84 hr; however, the maximum biofilm thickness (24 µm) was recorded after 60 hr of growth. Planktonic growth of the SRB strain showed a log phase up to 48 hr and the sulphide production ranged from 2 to 14 mg l−1. For a comparative account, the SRB biofilm formation on copper was chosen as a positive control. Finally, the putative role of extracellular electron transfer by SRB in the biocorrosion process and the plausible mechanism of pitting corrosion of titanium is described in detail.

Utilization of lead ions to improve surface hydrophobicity and flotation recovery of sulfidized smithsonite

Zinc oxide minerals often coexist with lead minerals in ores, and lead ions (Pb2+) dissolve from lead minerals during grinding and slurry stirring. These dissolved Pb2+ ions affect the surface properties of zinc oxide minerals and the interaction between the mineral surface and flotation reagents, causing a change of the flotation behavior of the zinc oxide minerals. In this study, we systematically investigated the effect of Pb2+ on the surface hydrophobicity and flotation behavior of sulfidized smithsonite in xanthate flotation. The smithsonite floatability was enhanced when Pb2+ was present in the pulp after sulfidization, and the flotation recovery increased from 50.05% to 82.88%. Surface measurements indicated that the sulfide content on the smithsonite surfaces was higher for the smithsonite–Na2S–Pb2+ system than for the smithsonite–Na2S system, and the distribution of the sulfidization products was more compact. Furthermore, by addition of Pb2+ after sulfidization, the characteristic peak of xanthate appeared in the infrared spectrum of smithsonite, and the smithsonite contact angle increased from 36.38° to 60.35°. Therefore, interaction of Pb2+ with the sulfidized smithsonite surfaces enhanced the surface reactivity and promoted xanthate adsorption, thus improving the surface hydrophobicity, and creating favorable conditions to obtain an ideal flotation index.

Inhibition of endogenous hydrogen sulfide production suppresses the growth of nasopharyngeal carcinoma cells.

Hydrogen sulfide (H2 S) has been widely recognized as one of gasotransmitters. Endogenous H2 S plays a crucial role in the progression of cancer. However, the effect of endogenous H2 S on the development of nasopharyngeal carcinoma (NPC) is still unknown. In this study, aminooxyacetic acid (AOAA, an inhibitor of cystathionine-β-synthase), dl-propargylglycine (PAG, an inhibitor of cystathionine-γ-lyase), and l-aspartic acid (l-Asp, an inhibitor of 3-mercaptopyruvate sulfurtransferase) were adopted to detect the role of endogenous H2 S in NPC growth. The results indicated that the combine (PAG + AOAA + l-Asp) group had higher inhibitory effect on the growth of NPC cells than the PAG, AOAA, and l-Asp groups. There were similar trends in the levels of apoptosis and reactive oxygen species (ROS). In addition, the combine group exhibited lower levels of phospho (p)-extracellular signal-regulated protein kinase but higher expressions of p-p38 and p-c-Jun N-terminal kinase than those in the AOAA, PAG, and l-Asp groups. Furthermore, the combine group exerted more potent inhibitory effect on NPC xenograft tumor growth without obvious toxicity. In summary, suppression of endogenous H2 S generation could dramatically inhibit NPC growth via the ROS/mitogen-activated protein kinase pathway. Endogenous H2 S may be a novel therapeutic target in human NPC cells. Effective inhibitors for H2 S-producing enzymes could be designed and developed for NPC treatment.

Effect of Stoichiometry on Nanomagnetite Sulfidation.

Magnetite (Mt) has long been regarded as a stable phase with a low reactivity toward dissolved sulfide, but natural Mt with varying stoichiometries (the structural Fe(II)/Fe(III) ratio, xstru) might exhibit distinct reactivities in sulfidation. How Mt stoichiometry affects its sulfidation processes and products remains unknown. Here, we demonstrate that xstru is a master variable controlling the rates and extents of sulfide oxidation by magnetite nanoparticles (11 ± 2 nm). At pH = 7.0-8.0 and the initial Fe/S molar ratio of 10-50, the partially oxidized magnetite (xstru = 0.19-0.43) can oxidize dissolved sulfide to elemental sulfur (S0), but only surface adsorption of sulfide, without interfacial electron transfer (IET), occurs on the nearly stoichiometric magnetite (xstru = 0.47). The higher initial rate and extent of sulfide oxidation and S0 production are observed with the more oxidized magnetite that has the higher electron-accepting capability from surface-complexed sulfide (S(-II)(s)). The FeS clusters formed from magnetite sulfidation can be oxidized by the most oxidized magnetite with xstru = 0.19 but not by other magnetite particles. A linear relationship between the Gibbs free energy of reaction and the surface area-normalized initial rate of sulfide oxidation is observed in all experiments under the different conditions, suggesting the S(-II)(s)-magnetite IET dominates magnetite sulfidation at high Fe/S molar ratios and near-neutral pH.