Metalloproteomics Reveals Multi-Level Stress Response in Escherichia coli When Exposed to Arsenite.

The arsRBC operon encodes a three-protein arsenic resistance system. ArsR regulates the transcription of the operon, while ArsB and ArsC are involved in exporting trivalent arsenic and reducing pentavalent arsenic, respectively. Previous research into Agrobacterium tumefaciens 5A has demonstrated that ArsR has regulatory control over a wide range of metal-related proteins and metabolic pathways. We hypothesized that ArsR has broad regulatory control in other Gram-negative bacteria and set out to test this. Here, we use differential proteomics to investigate changes caused by the presence of the arsR gene in human microbiome-relevant Escherichia coli during arsenite (AsIII) exposure. We show that ArsR has broad-ranging impacts such as the expression of TCA cycle enzymes during AsIII stress. Additionally, we found that the Isc [Fe-S] cluster and molybdenum cofactor assembly proteins are upregulated regardless of the presence of ArsR under these same conditions. An important finding from this differential proteomics analysis was the identification of response mechanisms that were strain-, ArsR-, and arsenic-specific, providing new clarity to this complex regulon. Given the widespread occurrence of the arsRBC operon, these findings should have broad applicability across microbial genera, including sensitive environments such as the human gastrointestinal tract.

Arsenic-induced downregulation of BRWD3 suppresses proliferation and induces apoptosis in lung adenocarcinoma cells through the p53 and p65 pathways.

Bromodomain and WD-repeat domain-containing protein 3 (BRWD3) exhibits high expression in lung adenocarcinoma (LUAD) tissues and cells; however, its function in arsenic-induced toxicological responses remains unclear. This study aimed to investigate BRWD3 expression in response to arsenic-induced conditions and its impact on the proliferation and apoptosis of LUAD cell line SPC-A1 upon BRWD3 knockdown. The results revealed a decrease in BRWD3 expression in SPC-A1 cells treated with sodium arsenite (NaAsO2), but not sodium arsenite's metabolites. BRWD3 knockdown suppressed cell proliferation and induced apoptosis in SPC-A1 cells. Western blot analysis revealed that BRWD3 knockdown resulted in the upregulation of p53, phospho-p53-Ser392, and its downstream factors including MDM2, Bak, and Bax. Additionally, we observed the downregulation of p65, phospho-p65-Ser276, phospho-p65-Ser536, and its downstream factors, including IκBα, BIRC3, XIAP and CIAP1. Moreover, polymerase chain reaction analysis showed that BRWD3 knockdown also resulted in the downregulation of proliferation-related genes and upregulation of apoptosis-related genes. In conclusion, BRWD3 mediated proliferation and apoptosis via the p53 and p65 pathways in response to arsenic exposure, suggesting potential implications for LUAD treatment through BRWD3 downregulation by arsenic.

Rapid Oxidative Dissolution of Zerovalent Iron Induced by Sulfite for Efficient Removal of Arsenate and Arsenite: Selective Formation of Scorodite.

In this study, we proposed a moderate oxidation strategy for accelerating the oxidative dissolution of zerovalent iron (ZVI) using sulfite (S(IV)), thereby improving the removal of As(V) and As(III). Results revealed that, in the presence of 2.0 mM S(IV), both As(V) and As(III) were selectively converted into scorodite at pH0 3.0-7.0, while As(III) oxidation and As(V) immobilization were impressed over pH0 8.0-10.0. Batch experiments, radical quenching experiments, and electron spin resonance (ESR) measurements demonstrated that ZVI initially boosted S(IV) activation to generate SO4•-, •OH, and protons, and in turn, ZVI was further oxidized more intensely by these radicals than by oxygen. Concurrently, substantial protons derived from S(IV) oxidation neutralized hydroxyls produced by ZVI oxidation, maintaining an acidic environment conducive to the generation of scorodite rather than iron (hydr)oxides. Characterizations of X-ray diffraction (XRD), Raman, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM) confirmed that scorodite was formed in situ and then exfoliated from the surface of ZVI, and approximately 75% of ZVI could still be recovered, which contributed to efficient As removal in successive runs and real As-polluted wastewater. The application of S(IV) achieved a balance among ZVI reactivity improvement, As(V)/As(III) removal, and raw material consumption, making it a promising approach for addressing arsenic contamination in wastewater treatment.

N6-methyladenosine facilitates arsenic-induced neoplastic phenotypes of human bronchial epithelial cells by promoting miR-106b-5p maturation.

Arsenic is a widespread carcinogen and an important etiological factor for lung cancer. Dysregulated miRNAs have been implicated in arsenic carcinogenesis and the mechanisms of arsenic-induced dysregulated miRNAs have not been fully elucidated. N6-methyladenosine (m6A) modification is known to modulate pri-miRNA processing. However, whether m6A-mediated pri-miRNA processing is involved in arsenic carcinogenesis is poorly understood. Here, we found that m6A modification was significantly increased in arsenite-transformed human bronchial epithelial BEAS-2B cells (0.5 µM arsenite, 16 weeks). Meanwhile, METTL3 was significantly upregulated at week 12 and 16 during cell transformation. The proliferation, migration, invasion, and anchorage-independent growth of arsenite-transformed cells were inhibited by the reduction of m6A levels through METTL3 knockdown. Further experiments suggest that the oncogene miR-106b-5p is a potentially essential m6A target mediating arsenic-induced lung cancer. miR-106b-5p was observed to be upregulated after exposure to arsenite for 12 and 16 weeks, and the reduction of m6A levels caused by METTL3 knockdown inhibited miR-106b-5p maturation in arsenite-transformed cells. What's more, miR-106b-5p overexpression successfully rescued METTL3 knockdown-induced inhibition of the neoplastic phenotypes of transformed cells. Additionally, Basonuclin 2 (BNC2) was uncovered as a potential target of miR-106b-5p and downregulated by METTL3 via enhancing miR-106b-5p maturation. Additionally, the METTL3 inhibitor STM2457 suppressed neoplastic phenotypes of arsenite-transformed BEAS-2B cells by blocking pri-miR-106b methylation. These results demonstrate that m6A modification promotes the neoplastic phenotypes of arsenite-transformed BEAS-2B cells through METTL3/miR-106b-5p/BNC2 pathway, providing a new prospective for understanding arsenic carcinogenesis.

Effects of arsenic exposure on the PI3K/Akt/NF-κB signaling pathway in the hippocampus of offspring mice at different developmental stages.

The primary purpose of present study was to explore the effects of arsenic exposure on the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/nuclear transcription factor-κB (NF-κB) signaling pathway in the hippocampus of offspring mice at different developmental stages. Sodium arsenite (NaAsO2) at doses of 0, 15, 30 or 60 mg/L administered to female mice and their pups. The nuclear translocation levels of NF-κB were assessed by EMSA. Real-time RT-PCR was used to measure Akt, NF-κB and PI3K mRNA levels. Protein expressions of PI3K, p-Akt, inhibitor kappa B kinase (IKK), p-NF-κB, protein kinase A (PKA), inhibitor kappa B (IκB), and cAMP response element-binding protein (CREB) were measured by Western blot. Results disclosed that exposure to 60 mg/L NaAsO2 could suppress NF-κB levels of nuclear translocation of postnatal day (PND) 20 and PND 40 mice. Arsenic downregulated the transcriptional and translational levels of PI3K, Akt and NF-κB. Additionally, protein expressions of p-IKK, p-IκB, PKA and p-CREB also reduced. Taken together, results of present study indicated that arsenic could downregulate the PI3K/Akt/NF-κB signaling pathway, particularly on PND 40, which might be involved in the cognitive impairments.

Epicatechin ameliorates glucose intolerance and hepatotoxicity in sodium arsenite-treated mice.

Arsenic is a metalloid found in the environment that causes toxic effects in different organs, mainly the liver. This study aimed to investigate the protective effects of epicatechin (EC), a natural flavonol, on glucose intolerance (GI) and liver toxicity caused by sodium arsenite (SA) in mice. Our findings showed that SA exposure led to the development of GI. Liver tissue damage and decreased pancreatic Langerhans islet size were also observed in this study. Mice exposed to SA exhibited hepatic oxidative damage, indicated by reduced antioxidant markers (such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione), along with elevated levels of thiobarbituric acid reactive substances. SA administration elevated the serum activities of liver enzymes alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. Furthermore, notable increases in the levels of inflammatory and apoptotic markers (Toll-like receptor 4, nuclear factor-kappa B, tumor necrosis factor-α, nitric oxide, B-cell lymphoma-2, and cysteine aspartate-specific protease-3) were observed in the liver. Treatment of SA-exposed mice with EC considerably reversed these biochemical and histological changes. This study demonstrated the beneficial effects of EC in ameliorating SA-induced hyperglycemia and hepatotoxicity due to its ability to enhance the antioxidant system by modulating inflammation and apoptosis.

Enhanced capacity of thiol-functionalized sugarcane bagasse and rice husk biochars for arsenite sorption in aqueous solutions.

The utilization of biowastes for producing biochar to remove potentially toxic elements from water represents an important pathway for aquatic ecosystem decontamination. Here we explored the significance of thiol-functionalization on sugarcane bagasse biochar (Th/SCB-BC) and rice husk biochar (Th/RH-BC) to enhance arsenite (As(III)) removal capacity from water and compared their efficiency with both pristine biochars (SCB-BC and RH-BC). The maximum As(III) sorption was found on Th/SCB-BC and Th/RH-BC (2.88 and 2.51 mg g-1, respectively) compared to the SCB-BC and RH-BC (1.51 and 1.40 mg g-1). Relatively, a greater percentage of As(III) removal was obtained with Th/SCB-BC and Th/RH-BC (92% and 83%, respectively) at a pH 7 compared to pristine SCB-BC and RH-BC (65% and 55%) at 6 mg L-1 initial As(III) concentration, 2 h contact time and 1 g L-1 sorbent dose. Langmuir (R2 = 0.99) isotherm and pseudo-second-order kinetic (R2 = 0.99) models provided the best fits to As(III) sorption data. Desorption experiments indicated that the regeneration ability of biochars decreased and it was in the order of Th/SCB-BC (88%) > Th/RH-BC (82%) > SCB-BC (77%) > RH-BC (69%) up to three sorption-desorption cycles. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy results demonstrated that the thiol (-S-H) functional groups were successfully grafted on the surface of two biochars and as such contributed to enhance As(III) removal from water. Spectroscopic data indicated that the surface functional moieties, such as -S-H, - OH, - COOH, and C = O were involved to increase As(III) sorption on thiol-functionalized biochars. This study highlights that thiol-grafting on both biochars, notably on SCB-BC, enhanced their ability to remove As(III) from water, which can be used as an effective technique for the treatment of As from drinking water.

Melatonin alleviates arsenic-induced liver injury by regulating protein RKIP and enhancing antioxidant defencse mechanisms.

Arsenic (As) is a highly toxic metal and one of the main factors in cancer development through oxidative stress and production of reactive oxygen species. Prior research has demonstrated melatonin's potential as a free radical scavenger. Raf kinase inhibitory protein (RKIP) is an important regulator of intracellular signaling pathways that has been linked to various types of cancer. The aim of this research was to explore the influence of melatonin's antioxidant properties on the expression of the protein RKIP and the antioxidant status of liver tissue in rats that were exposed to arsenic. Thirty two male Wistar rats were divided into four groups of eight, including control, melatonin-treated (20 mg/Kg of melatonin), sodium arsenite-treated (5.5 mg/Kg of sodium arsenite), and melatonin + sodium arsenite-treated groups (combination) for 4 weeks. The expression level of protein RKIP was measured by Western blot, and malondialdehyde (MDA) content of the liver as well as the activities of antioxidant enzymes were measured. The data analyzed using one-way ANOVA (significance level of p < 0.05) and GraphPad Prism (9) software. Sodium arsenite treatment led to a significant decrease in RKIP protein expression and antioxidant enzyme activity, and an increase in liver MDA levels (p < 0.001). Conversely, melatonin treatment in the combination group resulted in a significant increase in RKIP protein expression and antioxidant enzyme activity and a decrease in liver MDA levels (p < 0.05). These findings suggest that melatonin can attenuate oxidative damage caused by arsenic in liver cells by enhancing RKIP protein expression and antioxidant enzyme activity.

Foliar-selenium enhances plant growth and arsenic accumulation in As-hyperaccumulator Pteris vittata: Critical roles of GSH-GSSG cycle and arsenite antiporters PvACR3.

It is known that selenium (Se) enhances plant growth and arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated mechanisms are unclear. In this study, P. vittata was exposed to 50 µM arsenate (AsV) under hydroponics plus 25 or 50 µM foliar selenate. After 3-weeks of growth, the plant biomass, As and Se contents, As speciation, malondialdehyde (MDA) and glutathione (GSH and GSSG) levels, and important genes related to As-metabolism in P. vittata were determined. Foliar-Se increased plant biomass by 17 - 30 %, possibly due to 9.1 - 19 % reduction in MDA content compared to the As control. Further, foliar-Se enhanced the As contents by 1.9-3.5 folds and increased arsenite (AsIII) contents by 64 - 136 % in the fronds. The increased AsV reduction to AsIII was attributed to 60 - 131 % increase in glutathione peroxidase activity, which mediates GSH oxidation to GSSG (8.8 -29 % increase) in the fronds. Further, foliar-Se increased the expression of AsIII antiporters PvACR3;1-3;3 by 1.6 - 2.1 folds but had no impact on phosphate transporters PvPht1 or arsenate reductases PvHAC1/2. Our results indicate that foliar-Se effectively enhances plant growth and arsenic accumulation by promoting the GSH-GSSG cycle and upregulating gene expression of AsIII antiporters, which are responsible for AsIII translocation from the roots to fronds and AsIII sequestration into the fronds. The data indicate that foliar-Se can effectively improve phytoremediation efficiency of P. vittata in As-contaminated soils.

Exposure to four typical heavy metals induced telomere shortening of peripheral blood mononuclear cells in relevant with declined urinary aMT6s in rats.

Environmental heavy metals pollution have seriously threatened the health of human beings. An increasing number of researches have demonstrated that environmental heavy metals can influence the telomere length of Peripheral Blood Mononuclear Cells (PBMCs), which implicate biological aging as well as predicts diseases. Our previous study has shown that methylmercury (MeHg)-induced telomere shortening in rat brain tissue was associated with urinary melatonin metabolite 6-sulfatoxymelatonin (aMT6s) levels. Here, we aimed to further elucidate the impact of 4 typical heavy metals (As, Hg, Cd and Pb) on telomere length of PBMCs and their association with urinary aMT6s in rats. In this study, eighty-eight male Sprague-Dawley rats were randomized grouped into eleven groups. Among them, forty 3-month-old (young) and forty 12-month-old (middle-aged) rats were divided into young or middle-aged control groups as well as typical heavy metals exposed groups, respectively. Eight 24-month-old rats (old) was divided into aging control group. The results showed that MeHg exposure in young rats while sodium arsenite (iAs), MeHg, cadmium chloride (CdCl2), lead acetate (PbAc) exposure in middle-aged rats for 3 months significantly reduced the levels of and urinary aMT6s, as well as telomere length of PBMCs. In addition, they also induced abnormalities in serum oxidative stress (SOD, MDA and GPx) and inflammatory (IL-1ß, IL-6 and TNF-α) indicators. Notably, there was a significant positive correlation between declined level of urinary aMT6s and the shortening of telomere length in PBMCs in rats exposed to 4 typical heavy metals. These results suggested that 4 typical heavy metals exposure could accelerate the reduction of telomere length of PBMCs partially by inducing oxidative stress and inflammatory in rats, while ageing may be an important synergistic factor. Urinary aMT6s detection may be a alternative method to reflect telomere toxic effects induced by heavy metal exposure.

The activation of TLR4-MyD88 signaling promotes hepatic dysfunction and fibrotic changes in SD rats resulting from prolonged exposure to sodium arsenite.

Arsenic, a poisonous metalloid element, is linked to liver diseases, but the exactmechanisms for this process are not yet to be completely elucidated. Toll like receptor 4 (TLR4), acting as a pathogenic pattern recognition receptor, plays a pivotal role in various inflammatory diseases via the myeloid differentiation factor 88 (MyD88) pathway. This study aims to investigate the involvement of the TLR4-MyD88 signaling pathway in liver injury induced by prolonged exposure to sodium arsenite (NaAsO2) in Sprague-Dawley rats. Our research findings demonstratethe activation of TLR4-MyD88 signaling pathway in long-term NaAsO2-exposed rat liver tissues, leading to a significant release of inflammatory factors, which suggests its potential involvement in the pathogenesis of NaAsO2-induced liver injury. We further administered lipopolysaccharide (LPS), a natural ligand of TLR4, and TAK-242, a specific inhibitor of TLR4, to rats in order to validate the specific involvement of the TLR4-MyD88 signaling pathway in NaAsO2-induced liver injury. The results showed that, 1 mg/kg.bw LPS treatment significantly activated TLR4-MyD88 signalling pathway and its mediated pro-inflammatory factors, leading to up-regulation of activation indicators in hepatic stellate cells (HSCs) as well as increased secretion levels of extracellular matrix (ECM) in the liver, and ultimately induced liver fibrosis and dysfunction in rats. Relevantly, subsequent administration of 0.5 mg/kg.bw TAK-242 significantly attenuated the expression levels of TLR4 and its associated proteins, mitigated collagen deposition, and partially improved liver fibrosis and dysfunction caused by NaAsO2 in rats. Our study fully confirms the pivotal role of the TLR4-MyD88 signaling in promoting liver injury induced by NaAsO2, thereby providing a novel molecular target for preventing and treating patients with arsenic poisoning-related liver injury.

Sustained high expression of NRF2 inhibits cell apoptosis in arsenite-transformed human keratinocytes.

Our previous study identified that nuclear factor-erythroid-2 p45-related factor 2 (NRF2) was activated in arsenite-induced tumorigenesis. However, the underlying mechanisms of NRF2 mediating apoptosis in arsenic-induced skin carcinogenesis remain unknown. This study explored the dynamic changes in apoptosis rate and the expression of apoptosis proteins in immortalized human keratinocytes (HaCaT) malignant transformation caused by 1.0 µM NaAsO2 at passages 0, 1, 7, 14, 21, 28, and 35. The result showed that the apoptosis rate decreased. The apoptosis-related proteins cleaved-caspase-3/caspase-3 ratio decreased in the later stages (passages 21, 28, and 35). Moreover, the expression of intrinsic ER stress pathway-related CHOP, ATF4, ATF6, and the intrinsic mitochondrial pathway-related Bax protein decreased in the later stages, while Bcl-2 and Mcl-1 increased, and NRF2 protein levels also increased. The apoptosis rate increased by silencing NRF2 expression in arsenite-transformed HaCaT (T-HaCaT) cells. Meanwhile, the expression of pro-apoptotic proteins (cleaved-caspase-3/caspase-3, CHOP, Bax) and ATF4, ATF6 increased. On the contrary, antiapoptotic protein levels (Bcl-2 and Mcl-1) decreased. The ability of colony formation and migration of T-HaCaT cells decreased. In conclusion, arsenite activated NRF2 in the later stages, decreasing apoptosis characterized by inhibiting endoplasmic reticulum stress-depended and mitochondria-depended apoptosis pathway, and further promoting NaAsO2-induced HaCaT cellular malignant transformation.

Biological arsenite oxidation on iron-based adsorbents in groundwater filters.

Iron-based adsorbents are commonly used to remove arsenic (As) from water for drinking water purposes. Here, we study the role of biological As(III) oxidation on iron-based adsorbents in filters and its effect on overall As uptake. A lab-scale filter with iron oxide coated sand (IOCS), a commonly used adsorbent, was operated with water containing As(III) and As(V), while water samples were taken periodically over its height. As(III) oxidation initiated after approximately 10 days and increased to a first order rate constant of 0.09 s-1 after 57 days resulting in full oxidation of As(III) in <50 s. Consequently, the filter shifted from an As(III) to an As(V) adsorbing filter. Oxidation was not observed after inhibiting the microbial activity using sodium azide confirming its biogenic nature. This implies that As(III) oxidizing biomass can grow on iron-based adsorbents in water filters without requiring inoculation. As the experimental conditions were similar to full-scale As treatment plants, we believe that biological As(III) oxidation is widely overlooked in these systems. Occurrence of biological oxidation is, however, beneficial for removal, as at pH <8 the adsorption capacity for As(V) can be up to 10-fold higher than for As(III). With these new insights, arsenic treatment using iron-based adsorbents can be further optimized. We suggest a more robust new design with a biological active As(III) oxidizing top layer and an As(V) adsorbing bottom layer.

Impact of ionic strength on goethite colloids co-transported with arsenite (As3+) through a saturated sand column under anoxic condition: Experiment and mathematical modeling.

The knowledge about co-transport of goethite and As3+ to investigate the effect of goethite colloids on As3+ transport under various degrees of seawater intrusion, particular extremely conditions, in groundwater environment is still limited. The main objective is to investigate the influence of seawater intrusion on the sorption, migration, and reaction of As3+and goethite colloids into sand aquifer media under anoxic conditions by using the bench-scale and reactive geochemical modeling. The research consisted of two parts as follows: 1) column transport experiments consisting of 8 columns, which were packed by using synthesis groundwater at IS of 0.5, 50, 200, and 400 mM referring to the saline of seawater system in the study area, and 2) reactive transport modeling, the mathematical model (HYDRUS-1D) was applied to describe the co-transport of As3+ and goethite. Finally, to explain the interaction of goethite and As3+, the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation was considered to support the experimental results and HYDRUS-1D model. The results of column experiments showed goethite colloids can significantly inhibit the mobility of As3+ under high IS conditions (>200 mM). The Rf of As3+ bound to goethite grows to higher sizes (47.5 and 65.0 µm for 200 and 400 mM, respectively) of goethite colloid, inhibiting As3+ migration through the sand columns. In contrast, based on Rf value, goethite colloids transport As3+ more rapidly than a solution with a lower IS (0.5 and 50 mM). The knowledge gained from this study would help to better understand the mechanisms of As3+ contamination in urbanized coastal groundwater aquifers and to assess the transport of As3+ in groundwater, which is useful for groundwater management, including the optimum pumping rate and long-term monitoring of groundwater quality.

Assessing the impact of arsenite and arsenate on Sarcodia suae: a tale of two toxicities.

Inorganic arsenic (iAs), which predominantly occurs as arsenite (As3+) and arsenate (As5+) in natural water, is primarily accumulated by seaweed in marine environments. However, the detailed mechanisms through which As3+ and As5+ affect the physiological processes of these organisms remain largely unknown. This study focused on evaluating the toxicological effects of As3+ and As5+ on the seaweed Sarcodia suae. Exposure to As3+ and As5+ resulted in IC50 values of 401.5 ± 9.4 µg L-1 and 975.8 ± 13 µg L-1, respectively. Morphological alterations and a reduction in phycoerythrin content were observed, particularly under As3+ exposure, with increased lipid peroxidation as evidenced by higher malondialdehyde levels. Exposure to As3+ also elevated the production of superoxide radicals, while decreasing hydrogen peroxide levels specifically in the presence of As3+. The induction of antioxidative enzyme activities, namely superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase was observed, signaling an adaptive response to iAs-induced oxidative stress. Moreover, levels of the antioxidants ascorbate and glutathione were elevated post-exposure, especially in response to As3+. Additionally, bioaccumulation of arsenic was significantly higher in the As3+ compared to As5+. Collectively, the data suggest that As3+ imposes greater adverse effects and oxidative stress to S. suae, which responds by adjusting its antioxidative defense mechanisms to mitigate oxidative stress.

A Sb(III)-specific efflux transporter from Ensifer adhaerens E-60.

Antimony is pervasive environmental toxic substance, and numerous genes encoding mechanisms to resist, transform and extrude the toxic metalloid antimony have been discovered in various microorganisms. Here we identified a major facilitator superfamily (MFS) transporter, AntB, on the chromosome of the arsenite-oxidizing bacterium Ensifer adhaerens E-60 that confers resistance to Sb(III) and Sb(V). The antB gene is adjacent to gene encoding a LysR family transcriptional regulator termed LysRars, which is an As(III)/Sb(III)-responsive transcriptional repressor that is predicted to control expression of antB. Similar antB and lysRars genes are found in related arsenic-resistant bacteria, especially strains of Ensifer adhaerens, and the lysRars gene adjacent to antB encodes a member of a divergent subgroup of putative LysR-type regulators. Closely related AntB and LysRars orthologs contain three conserved cysteine residues, which are Cys17, Cys99, and Cys350 in AntB and Cys81, Cys289 and Cys294 in LysRars, respectively. Expression of antB is induced by As(III), Sb(III), Sb(V) and Rox(III) (4-hydroxy-3-nitrophenyl arsenite). Heterologous expression of antB in E. coli AW3110 (Δars) conferred resistance to Sb(III) and Sb(V) and reduced the intracellular concentration of Sb(III). The discovery of the Sb(III) efflux transporter AntB enriches our knowledge of the role of the efflux transporter in the antimony biogeochemical cycle.

Effects of developmental exposure to arsenic species on behavioral stress responses in larval zebrafish and implications for stress-related disorders.

Arsenic (As) is globally detected in drinking water and food products at levels repeatedly surpassing regulatory thresholds. Several neurological and mental health risks linked to arsenic exposure are proposed; however, the nature of these effects and their association with the chemical forms of arsenic are not fully understood. Gaining a clear understanding of the etiologies and characteristics of these effects is crucial, particularly in association with developmental exposures where the nervous system is most vulnerable. In this study, we investigated the effects of early developmental exposure (6- to 120-h postfertilization [hpf]) of larval zebrafish to environmentally relevant concentrations of arsenic species-trivalent/pentavalent, inorganic/organic forms-on developmental, behavioral, and molecular endpoints to determine their effect on stress response and their potential association with stress-related disorders. At 120 hpf, the developing larvae were assessed for a battery of endpoints including survival, developmental malformities, background activity, and behavioral responses to acute visual and acoustic stimuli. Pooled larval samples were analyzed for alterations in the transcript levels of genes associated with developmental neurotoxicity and stress-related disorders. Developmental exposures at target concentrations did not significantly alter survival, overall development, or background activity, and had minor effects on developmental morphology. Sodium arsenate and monomethylarsonic acid exaggerated the behavioral responses of larval zebrafish, whereas sodium arsenite depressed them. Sodium arsenate induced significant effects on molecular biomarkers. This study highlights the effects of developmental exposure to arsenicals on the behavioral stress response, the role chemical formulation plays in exerting toxicological effects, and the possible association with stress-related disorders.

The mRNA-capping enzyme localizes to stress granules in the cytoplasm and maintains cap homeostasis of target mRNAs.

The model of RNA stability has undergone a transformative shift with the revelation of a cytoplasmic capping activity that means a subset of transcripts are recapped autonomously of their nuclear counterparts. The present study demonstrates nucleo-cytoplasmic shuttling of the mRNA-capping enzyme (CE, also known as RNA guanylyltransferase and 5'-phosphatase; RNGTT), traditionally acknowledged for its nuclear localization and functions, elucidating its contribution to cytoplasmic capping activities. A unique nuclear export sequence in CE mediates XPO1-dependent nuclear export of CE. Notably, during sodium arsenite-induced oxidative stress, cytoplasmic CE (cCE) congregates within stress granules (SGs). Through an integrated approach involving molecular docking and subsequent co-immunoprecipitation, we identify eIF3b, a constituent of SGs, as an interactive associate of CE, implying that it has a potential role in guiding cCE to SGs. We measured the cap status of specific mRNA transcripts from U2OS cells that were non-stressed, stressed and recovered from stress, which indicated that cCE-target transcripts lost their caps during stress but remarkably regained cap stability during the recovery phase. This comprehensive study thus uncovers a novel facet of cytoplasmic CE, which facilitates cellular recovery from stress by maintaining cap homeostasis of target mRNAs.

Arsenate reductase of Rufibacter tibetensis is a metallophosphoesterase evolved to catalyze redox reactions.

An arsenate reductase (Car1) from the Bacteroidetes species Rufibacter tibetensis 1351T was isolated from the Tibetan Plateau. The strain exhibits resistance to arsenite [As(III)] and arsenate [As(V)] and reduces As(V) to As(III). Here we shed light on the mechanism of enzymatic reduction by Car1. AlphaFold2 structure prediction, active site energy minimization, and steady-state kinetics of wild-type and mutant enzymes give insight into the catalytic mechanism. Car1 is structurally related to calcineurin-like metallophosphoesterases (MPPs). It functions as a binuclear metal hydrolase with limited phosphatase activity, particularly relying on the divalent metal Ni2+. As an As(V) reductase, it displays metal promiscuity and is coupled to the thioredoxin redox cycle, requiring the participation of two cysteine residues, Cys74 and Cys76. These findings suggest that Car1 evolved from a common ancestor of extant phosphatases by incorporating a redox function into an existing MPP catalytic site. Its proposed mechanism of arsenate reduction involves Cys74 initiating a nucleophilic attack on arsenate, leading to the formation of a covalent intermediate. Next, a nucleophilic attack of Cys76 leads to the release of As(III) and the formation of a surface-exposed Cys74-Cys76 disulfide, ready for reduction by thioredoxin.

Arsenite oxidation and adsorptive arsenic removal from contaminated water: a review.

Arsenic poisoning of groundwater is one of the most critical environmental hazards on Earth. Therefore, the practical and proper treatment of arsenic in water requires more attention to ensure safe drinking water. The World Health Organization (WHO) sets guidelines for 10 µg/L of arsenic in drinking water, and direct long-term exposure to arsenic in drinking water beyond this value causes severe health hazards to individuals. Numerous studies have confirmed the adverse effects of arsenic after long-term consumption of arsenic-contaminated water. Here, technologies for the remediation of arsenic from water are highlighted for the purpose of understanding the need for a single-point solution for the treatment of As(III)-contaminated water. As(III) species are neutral at neutral pH; the solution requires transformation technology for its complete removal. In this critical review, emphasis was placed on single-step technologies with multiple functions to remediate arsenic from water.