Arsenic Methylation Research Articles

Arsenic Methylation by a Sulfate-Reducing Bacterium from Paddy Soil Harboring a Novel ArsSM Fusion Protein.

Microbial arsenic (As) methylation is an important process of As biogeochemistry. Only a few As-methylating microorganisms have been isolated from paddy soil, hindering the mechanistic understanding of the process involved. We isolated 54 anaerobic and 32 aerobic bacteria from paddy soil with a high As methylation potential. Among the 86 isolates, 14 anaerobes, including 7 sulfate-reducing bacteria (SRB), but none of the aerobes were able to methylate arsenite [As(III)] or monomethylarsenite [MMA(III)] or both, suggesting that the As-methylating ability is much more prevalent in anaerobes than in aerobes. We performed a detailed investigation on As methylation by a SRB isolate, Solidesulfovibrio sp. TC1, and identified a novel bifunctional enzyme consisting of a fusion of As(III) S-adenosylmethionine (SAM) methyltransferase (ArsM) and a radical SAM protein. The enzyme (ArsSM) can catalyze As(III) methylation to MMA and DMA and subsequent adenosylation of DMA to form 5'-deoxy-5'-dimethylarsinoyl-adenosine (DDMAA), which is a key intermediate in the biosynthesis of arsenosugars. High concentrations of sulfide produced by SRB did not affect As(III) methylation to MMA but inhibited MMA methylation to DMA. Genes encoding ArsSM fusion proteins are widespread in anaerobes, particularly SRB, suggesting that ArsSM-carrying anaerobes may play an important role in As methylation in an anoxic environment.

Midseason draining of paddy water suppresses microbial arsenic methylation in soil and alleviates rice straighthead disease

Arsenic (As) methylation is an important component of As biogeochemical cycle. Microbial As methylation is enhanced under anoxic conditions in paddy soil, producing dimethylarsenate (DMA) which can cause physiological straighthead disease in rice. We conducted field experiments at two sites to test the effect of midseason draining of paddy water on microbial As methylation and the incidence of straighthead disease. Compared to continuous flooding, midseason draining increased soil Eh, decreased the abundances of microbial genes for arsenate reduction (arsC and arrA) and arsenite methylation (arsM), and lowered the concentrations of both inorganic As and DMA in soil porewater. Draining shifted microbial composition, resulting in decreases in the relative abundance of 17–132 amplicon sequence variants. Draining decreased the accumulation of DMA in rice husk and of inorganic As and DMA in rice grain, decreased the incidence of straighthead disease, and increased grain yield by 20–45 %. Further experiments were conducted at eight field sites to assess the effect of midseason draining in a split field design. Draining decreased husk DMA concentration by 40–65 % and increased grain yield by 25–209 %. This study demonstrates that midseason draining can effectively suppress microbial As methylation and alleviate rice straighthead disease, benefiting both grain yield and safety.

Biotransformations of arsenic in marine sediments across marginal slope to hadal zone

Arsenic compounds are accumulating in deep ocean, but their ecological impacts on deep-sea ecosystem remain elusive. We studied 32 sediment cores (101 layers for metagenomes, along with 41 global reference sediment metagenomes) collected from the South China Sea and the Mariana Trench (MT), characterized with high arsenic accumulation in MT. In these metagenomes we revealed a significantly positive correlation between relative abundance of arsenite methyltransferase gene (arsM) and sampling depth, which suggests that arsenic methylation is the most prevalent arsenic biotransformation process in the deep sea. Lower relative abundance of arsenic efflux gene, compared with arsM, indicates that microbes in deep-sea sediments were prone to methylate arsenite and retain it rather than efflux it. Phylogenetic analysis identified seven clades of ArsM proteins, including two new clades derived primarily from deep-sea microorganisms. Five metagenome-assembled genomes containing aioA for arsenite oxidation also harbor carbon fixation genes in the deep-sea sediment layers, suggesting previously unnoticed contribution of arsenite-oxidizing autotrophic bacteria to the carbon cycle. Therefore, deep-sea microorganisms adopt different detoxification and transformation strategies in response to arsenic compounds, which renews our understanding of arsenic in their ecological impacts and potential contribution in deep ocean.

Differential Selectivity of Human and Mouse ABCC4/Abcc4 for Arsenic Metabolites.

Millions of people globally are exposed to the proven human carcinogen arsenic at unacceptable levels in drinking water. In contrast, arsenic is a poor rodent carcinogen, requiring >100-fold higher doses for tumour induction, which may be explained by toxicokinetic differences between humans and mice. The human ATP-binding cassette (ABC) transporter hABCC4 mediates the cellular efflux of a diverse array of metabolites, including the GSH conjugate of the highly toxic monomethylarsonous acid (MMAIII), MMA(GS)2, and the major human urinary arsenic metabolite dimethylarsinic acid (DMAV). Our objective was to determine if mouse Abcc4 (mAbcc4) protected against and/or transported the same arsenic species as hABCC4. The anti-ABCC4 antibody M4I-10 epitope was first mapped to an octapeptide (411HVQDFTA418F) present in both hABCC4 and mAbcc4, enabling quantification of relative amounts of hABCC4/mAbcc4. mAbcc4 expressed in HEK293 cells did not protect against any of the six arsenic species tested [arsenite, arsenate, MMAIII, monomethylarsonic acid, dimethylarsinous acid or DMAV], despite displaying remarkable resistance against the antimetabolite 6-mercaptopurine (>9-fold higher than hABCC4). Furthermore, mAbcc4-enriched membrane vesicles prepared from transfected HEK293 cells did not transport MMA(GS)2 or DMAV, despite a >3-fold higher transport activity than hABCC4-enriched vesicles for the prototypic substrate 17β-estradiol-17-(β-D-glucuronide). Abcc4(+/+) mouse embryonic fibroblasts (MEFs) were ~3-fold more resistant to arsenate than Abcc4(-/-) MEFs; however, further characterization indicated this was not mAbcc4 mediated. Thus, under the conditions tested, arsenicals are not transported by mAbcc4, and differences between the substrate selectivity of hABCC4 and mAbcc4 seem likely to contribute to differences in human and mouse arsenic toxicokinetics. Significance Statement Toxicokinetics of the carcinogen arsenic differ among animal species. Arsenic methylation is known to contribute to this, whereas arsenic transporters have not been considered. The human ATP-binding cassette transporter hABCC4 is a high affinity transporter of toxicologically important arsenic metabolites. Here we used multiple cell models to demonstrate that mouse Abcc4 does not protect cells against, or transport, any arsenic species tested. Thus, differences between hABCC4 and mAbcc4 substrate selectivity likely contribute to differences in human and mouse arsenic toxicokinetics.

Microplastics and arsenic speciation in edible bivalves from the coast of China: Distribution, bioavailability, and human health risk

Bivalves, such as oysters and mussels, are exposed to environmental pollutants, like microplastics (MPs) and arsenic (As). This study investigated co-existence and interaction of MPs and As (total As and As species) in two bivalve species from the Chinese coastline. Smaller MPs (20–100 μm) averaged 30.98 items/g, while larger MPs (100–500 μm) averaged 2.98 items/g. Oysters contained more MPs (57.97 items/g) in comparison to mussels (11.10 items/g). In Contrast, mussels had a higher As concentrations (8.36–23.65 mg/kg) than oysters (4.97–11.02 mg/kg). The size and composition of MPs influenced As uptake and speciation in bivalves, with inorganic arsenic (iAs) and methylated arsenic (MMA and DMA) correlating with larger-sized MPs. Polyethylene (PE) may interact with the formation of arsenobetaine (AsB) in oyster. This study provides valuable insights into the interaction of MPs and As in marine ecosystems and highlights their implications for food safety.

Organic food and internal exposure to pollutants among Flemish adolescents.

Contrary to the initial hypothesis, Flemish adolescents who reported consuming organic food at least 7.5 times per week did not exhibit reduced internal exposure to the tested recently used pesticides. After adjustment for gender, age, country of origin, socioeconomic status, body mass index, consumption of high-fat foods and foods linked to organic food consumption, and concerning organochlorine derivatives and lead, additional adjustment for the duration of breastfeeding expressed in weeks, they displayed slightly elevated internal exposure to organochlorine derivatives, lead, methyl arsenate, and toxic relevant arsenic. A comparison was also made between the correlation of internal exposure to pollutants with the frequency of organic food consumption on one hand and the total consumption of equivalent products from all sources on the other. Regarding potatoes, vegetables, and fruits, no clear trends were observed. Regarding eggs, there was a trend towards higher internal exposures with organic food consumption, significant for trans-nonachlor, PCB118, and 2,4-dichlorophenoxyacetic acid, and marginally significant for glyphosate. For dairy, there was a trend towards higher internal exposures with organic food consumption, significant for perfluorononanoic acid and marginally significant for PCB153. Regarding nuts and seeds, the higher internal exposure to dichlorophenoxyacetic acid and the lower exposure to 3-phenoxybenzoic acid were marginally significant, while there was also a trend towards higher internal exposure to other pollutants with organic food consumption, significant for PCB118, PCB153, and sum PCBs, and marginally significant for trans-nonachlor. Concerning breakfast cereals and muesli, no clear trends were observed.

Reduced Arsenic Methylation Capacity in Young Chinese Adults After Short-Term Arsenic Exposure From Rice

Reduced Arsenic Methylation Capacity in Young Chinese Adults After Short-Term Arsenic Exposure From Rice

Alterations of Arsenic Methylation Among Young Chinese Adults on a Wheat Diet Followed by a Rice Diet

Alterations of Arsenic Methylation Among Young Chinese Adults on a Wheat Diet Followed by a Rice Diet

B vitamins for arsenic methylation in children and adults in Bangladesh

B vitamins for arsenic methylation in children and adults in Bangladesh

Biochemical investigation of association of arsenic exposed polymorphic variants and disease susceptibility

Our study aimed to establish the association of polymorphic variants and disease susceptibility in arsenic-induced metabolic disorders raised due to the variability of arsenic methylation in human population exposed to arsenic in drinking water. Water samples were systematically collected from various regions of Faisalabad, Pakistan, and subjected to arsenic quantification through inductively coupled plasma emission spectrophotometry (ICP-OES). The groundwater exhibited significantly elevated arsenic concentrations (68.18 ± 21.28 μg/L) in comparison to both water and sanitation agency Faisalabad (WASA)-supplied water (9.81 ± 1.2 μg/L) and locally filtered water (8.12 ± 1.42 μg/L), as determined by one-way ANOVA followed by Bonferroni's post-test at P < 0.05. An association was established between arsenic concentration and the incidence of disease, such as diabetes mellitus. A cohort of 120 participants residing in six areas of District Faisalabad was recruited. Urine and blood specimens were collected for analysis. Urine samples underwent ICP-MS analysis in helium collision mode, utilizing germanium as an internal standard. Blood samples were collected for biomarker assessments, including HbA1c, BUN, creatinine, CRP, ALT, AST, GSH, SOD, and MDA, to investigate the evidence of diabetes mellitus. Urinary arsenic concentrations were found to be considerably higher (P < 0.05) in about 22.50 % of the participants, with a mean value of 68.43 ± 16.73 ppb. Biomarker analysis in these participants revealed mean values for BUN (37.19 ± 2.87 mg/dL), creatinine (2.58 ± 0.18 mg/dL), IL-6 (11.35 ± 6.98 pg/mL), CRP (1.90 ± 0.26 mg/dL), MDA (3.70 ± 0.18 nmol/mL), ALT (40.27 ± 5.41 U/L), and AST (38.92 ± 4.72 U/L). Furthermore, the gender-based analysis indicated the higher levels of DMA, MMA, TAs, and TiAs in males compared to females when urine samples were analyzed with HPLC-ICP-MS. Participants with the positive genotype of GSTM exhibited significantly higher levels of TAs, and TiAs concentration in their urine than those with the null genotype of GSTM. Moreover, participants with positive genotypes for GSTT1 and GSTM1 demonstrated elevated levels of DMA in their urine compared to those with genotypes of GSTT1 (−) and GSTM1 (−), although this difference did not attain statistical significance. Participants with the genotype of GSTT1 (+) displayed a considerably higher secondary methylation index than those with genotype of GSTT1 (−). MMA and DMA levels were found to be correlated with the genotypes of GSTT1 and GSTM1 and the amounts of TAs in urine. In conclusion, our findings suggest a linkage between arsenic methylation, particularly levels of DMA and SMI, and GSTT1 and GSTM1 polymorphisms.

Occurrence and spatiotemporal distribution of arsenic biotransformation genes in urban dust

Microbially-mediated arsenic biotransformation plays a pivotal role in the biogeochemical cycling of arsenic; however, the presence of arsenic biotransformation genes (ABGs) in urban dust remains unclear. To investigate the occurrence and spatiotemporal distributions of ABGs, a total of one hundred and eighteen urban dust samples were collected from different districts of Xiamen city, China in summer and winter. Although inorganic arsenic species, including arsenate [As(V)] and arsenite [As(III)], were found to be predominant, the methylated arsenicals, particularly trimethylarsine oxide [TMAs(V)O] and dimethylarsenate [DMAs(V)], were detected in urban dust. Abundant ABGs were identified in urban dust via AsChip analysis (a high-throughput qPCR chip for ABGs), of which As(III) S-adenosylmethionine methyltransferase genes (arsM), As(V) reductase genes (arsC), As(III) oxidase genes (aioA), As(III) transporter genes (arsB), and arsenic-sensing regulator genes (arsR) were the most prevalent, collectively constituting more than 90 % of ABGs in urban dust. Microbes involved in arsenic methylation were assigned to bacteria (e.g., Actinomycetes and Alphaproteobacteria), archaea (e.g., Halobacteria), and eukaryotes (e.g., Chlamydomonadaceae) in urban dust via the arsM amplicon sequencing. Temperature, a season-dependent environmental factor, profoundly affected the abundance of ABGs and the composition of microbes involved in arsenic methylation. This study provides new insights into the presence of ARGs within the urban dust.

The alleviation effect and its mechanism of Niuhuang Jiedu prescription on realgar-induced genotoxicity in mice

Ethnopharmacological relevanceRealgar (As2S2 or As4S4) is a traditional Chinese medicine (TCM) containing arsenic. Existing studies have shown that it has genotoxicity under long-term use with large doses. Niuhuang Jiedu (NHJD) is a Chinese medicine prescription containing realgar and seven other TCMs. Whether the multiple TCMs combination in NHJD can reduce the genotoxicity induced by realgar in equivalent doses is still unknown. Aim of the studyTo research the effect of NHJD on realgar's genotoxicity and the possible mechanism involved based on the arsenic methylation metabolic pathway. Material and methodsSix groups (control, realgar (0.8 g/kg), NHJD (12.48 g/kg), as well as Glycyrrhiza uralensis Fisch (GU), Scutellaria baicalensis Georg (SB), Rheum palmatum L (RP) plus equivalent doses of realgar, respectively) were set up. ICR mice were intragastric administered for 12 weeks. First, genotoxicology tests were conducted to evaluate the effect of NHJD, GU, SB, and RP on reducing realgar's genotoxicity. The inorganic arsenic (iAs), dimethyl arsenic acid (DMA), and monomethyl arsenic acid (MMA) were determined by HPLC-AFS, and the iAs%, MMA%, DMA%, primary methylation index (PMI), etc. Were calculated. Meanwhile, the S-adenosyl methionine (SAM) and arsenate reductase (ARR) levels, the arsenic (+3)methyltransferase (As3MT), purine-nucleoside phosphorylase (PNP), glutathione S-transfer omega1 (GSTO1) gene expression were detected, aimed to explore the possible alleviation mechanisms of NHJD. ResultsThe combination of multiple TCMs in NHJD decreased the levels of MN‰, SPA%, and DNA damage caused by realgar, with similar effects observed when SB, RP, and GU were used separately with realgar. Notably, the iAs% significantly decreased, while DMA% and PMI notably increased in the NHJD and realgar + SB (or RP) groups compared to the realgar-only group (P < 0.05). Increases in SAM and ARR levels were observed across various groups, but only the ARR increase in the NHJD group was statistically significant. Moreover, significant increases in As3MT mRNA and GSTO1 mRNA were noted in the NHJD group, and PNP mRNA levels significantly rose in the realgar + SB group. ConclusionsThis study revealed that NHJD could attenuate the genotoxic effects of realgar. The botanicals SB, RP, and GU within NHJD may be key contributors to this effect. Enhancements in arsenic methylation capabilities through increased levels of SAM and ARR and elevated gene expressions of As3MT, PNP, and GSTO1 suggest potential mechanisms behind these findings.

Remediation of arsenic- and nitrate-contaminated groundwater through iron-dependent autotrophic denitrifying culture

Groundwater contamination with arsenic and nitrate poses a pressing concern for the safety of local communities. Bioremediation, utilizing Fe(II)-oxidizing nitrate reducing bacteria, shows promise as a solution to this problem. However, the relatively weak environmental adaptability of a single bacterium hampers practical application. Therefore, this study explored the feasibility and characteristics of a mixed iron-dependent autotrophic denitrifying (IDAD) culture for effectively removing arsenic and nitrate from synthetic groundwater. The IDAD biosystem exhibited stable performace and arsenic resistance, even at a high As(III) concentration of 800 μg/L. Although the nitrogen removal efficiency of the IDAD biosystem decreased from 71.4% to 64.7% in this case, the arsenic concentration in the effluent remained below the standard (10 μg/L) set by WHO. The crystallinity of the lepidocrocite produced by the IDAD culture decreased with increasing arsenic concentration, but the relative abundance of the key iron-oxidizing bacteria norank_f_Gallionellaceae in the culture showed an opposite trend. Metagenomic analysis revealed that the IDAD culture possess arsenic detoxification pathways, including redox, methylation, and efflux of arsenic, which enable it to mitigate the adverse impact of arsenic stress. This study provides theoretical understanding and technical support for the remediation of arsenic and nitrate-contaminated groundwater using the IDAD culture.

Arsenic disulfide promoted the demethylation of PTPL1 in diffuse large B cell lymphoma cells.

Promoter hypermethylation of the tumor suppressor gene is one of the well-studied causes of cancer development. The drugs that reverse the process by driving demethylation could be a candidate for anticancer therapy. This study was designed to investigate the effects of arsenic disulfide on PTPL1 methylation in diffuse large B cell lymphoma (DLBCL). We knocked down the expression of PTPL1 in two DLBCL cell lines (i.e., DB and SU-DHL-4 cells) using siRNA. Then the DLBCL proliferation was determined in the presence of PTPL1 knockdown. The methylation of PTPL1 in DLBCL cells was analyzed by methylation specific PCR (MSPCR). The effect of arsenic disulfide on the PTPL1 methylation was determined in DLBCL cell lines in the presence of different concentrations of arsenic disulfide (5 µM, 10 µM and 20 µM), respectively. To investigate the potential mechanism on the arsenic disulfide-mediated methylation, the mRNA expression of DNMT1, DNMT3B and MBD2 was determined. PTPL1 functioned as a tumor suppressor gene in DLBCL cells, which was featured by the fact that PTPL1 knockdown promoted the proliferation of DLBCL cells. PTPL1 was found hypermethylated in DLBCL cells. Arsenic disulfide promoted the PTPL1 demethylation in a dose-dependent manner, which was related to the inhibition of DNMTs and the increase of MBD2. Experimental evidence shows that PTPL1 functions as a tumor suppressor gene in DLBCL progression. PTPL1 hyper-methylation could be reversed by arsenic disulfide in a dose-dependent manner.

Pathways and contributions of sulfate reducing-bacteria to arsenic cycling in landfills

Sulfate-reducing bacteria (SRB) are generally found in sanitary landfills and play a role in sulfur (S) and metal/metalloid geochemical cycling. In this study, we investigated the influence of SRB on arsenic (As) metabolic pathways in refuse-derived cultures. The results indicated that SRB promote As(III) methylation and are beneficial for controlling As levels. Heterotrophic and autotrophic SRB showed significant differences during As cycling. In heterotrophic SRB cultures, the As methylation rate increased with As(III) concentration in the medium and reached a peak (85.1%) in cultures containing 25 mg L−1 As(III). Moreover, 4.0–12.6% of SO42− was reduced to S2−, which then reacted with As(III) to form realgar (AsS). In contrast, autotrophic SRB oxidized As(III) to less toxic As(V) under anaerobic conditions. Heterotrophic arsM-harboring SRB, such as Desulfosporosinus, Desulfocurvibacter, and Desulfotomaculum, express As-related genes and are considered key genera for As methylation in landfills. Thiobacillus are the main autotrophic SRB in landfills and can derive energy by oxidizing sulfur compounds and metal(loid)s. These results suggest that different types of SRB drive As methylation, redox reaction, and mineral formation in landfills. These study findings have implications for the management of As pollutants in landfills and other contaminated environments.

Arsenic uptake and biotransformation mechanisms in Dunaliella salina: Insights into physiological and molecular responses

The biomass and premium extracts derived from D. salina possess diverse applications in industries like food, feed, health products, nutrition, pharmaceuticals, and cosmetics. However, D. salina's capacity to absorb and transform heavy metals, notably arsenic, can result in elevated arsenic concentrations in its products. This poses a challenge to large-scale D. salina breeding and introduces potential health risks. The impact of arsenic on D. salina product quality and the specific arsenic forms within its cells remain insufficiently understood. This study explores arsenic uptake and biotransformation mechanisms in D. salina exposed to arsenate (AsV) and arsenite (AsIII). Our findings highlight D. salina's preference for AsV, causing a significant rise in intracellular arsenic compared to AsIII exposure. Lower AsV concentrations facilitate arsenic methylation and organic transformation, influencing compound ratios. AsV triggers differential gene expression, upregulating metabolic pathways, arsenic transporters, and antioxidative defenses. Our results suggest that D. salina efficiently detoxifies arsenic by converting it into organoarsenicals, specifically arsenosugars and arsenicbetaine. This research offers valuable insights into microalgae's physiological and molecular responses to arsenic exposure, providing a foundation for understanding arsenic biotransformation mechanisms and potential applications in the large-scale breeding industry of D. salina.

Influence of folic acid and vitamin B12 supplementation on arsenic methylation: A double-blinded, placebo-controlled trial in Bangladeshi children

BackgroundInorganic arsenic is metabolized to monomethyl- (MMAs) and dimethyl- (DMAs) species via one-carbon metabolism (OCM); this facilitates urinary arsenic elimination. OCM is influenced by folate and vitamin B12 and previous randomized control trials (RCTs) showed that folic acid (FA) supplementation increases arsenic methylation in adults. This RCT investigated the effects of FA + B12 supplementation on arsenic methylation in children, a key developmental stage where OCM supports growth. MethodsA total of 240 participants (8–11 years, 53 % female) drinking from wells with arsenic concentrations > 50 μg/L, were encouraged to switch to low arsenic wells and were randomized to receive 400 μg FA + 5 μg B12 or placebo daily for 12-weeks. Urine and blood samples were collected at baseline, week 1 (only urine) and week 12. Generalized estimated equation (GEE) models were used to assess treatment effects on arsenic species in blood and urine. ResultsAt baseline, the mean ± SD total blood and urinary arsenic were 5.3 ± 2.9 μg/L and 91.2 ± 89.5 μg/L. Overall, total blood and urine arsenic decreased by 11.7% and 17.6%, respectively, at the end of follow up. Compared to placebo, the supplementation group experienced a significant increase in the concentration of blood DMAs by 14.0% (95% CI 5.0, 25.0) and blood secondary methylation index (DMAs/MMAs) by 0.19 (95% CI: 0.09, 0.35) at 12 weeks. Similarly, there was a 1.62% (95% CI: 0.43, 20.83) significantly higher urinary %DMAs and −1.10% (95% CI: −1.73, −0.48) significantly lower urinary %MMAs in the supplementatio group compared to the placebo group after 1 week. The direction of the changes in the urinary %iAs, %MMAs, and %DMAs at week 12 were consistent with those at week 1, though estimates were not significant. Treatment effects were stronger among participants with higher baseline blood arsenic concentrations. Results were consistent across males and females, and participants with higher and lower folate and B12 status at baseline. ConclusionThis RCT confirms that FA + B12 supplementation increases arsenic methylation in children as reflected by decreased MMAs and increased DMAs in blood and urine. Nutritional interventions may improve arsenic methylation and elimination in children, potentially reducing arsenic toxicity while also improving nutritional status.

Transgenerational Effects of Arsenic Exposure on Learning and Memory in Rats: Crosstalk between Arsenic Methylation, Hippocampal Metabolism, and Histone Modifications.

Arsenic (As) is widely present in the natural environment, and exposure to it can lead to learning and memory impairment. However, the underlying epigenetic mechanisms are still largely unclear. This study aimed to reveal the role of histone modifications in environmental levels of arsenic (sodium arsenite) exposure-induced learning and memory dysfunction in male rats, and the inter/transgenerational effects of paternal arsenic exposure were also investigated. It was found that arsenic exposure impaired the learning and memory ability of F0 rats and down-regulated the expression of cognition-related genes Bdnf, c-Fos, mGlur1, Nmdar1, and Gria2 in the hippocampus. We also observed that inorganic arsenite was methylated to DMA and histone modification-related metabolites were altered, contributing to the dysregulation of H3K4me1/2/3, H3K9me1/2/3, and H3K4ac in rat hippocampus after exposure. Therefore, it is suggested that arsenic methylation and hippocampal metabolism changes attenuated H3K4me1/2/3 and H3K4ac while enhancing H3K9me1/2/3, which repressed the key gene expressions, leading to cognitive impairment in rats exposed to arsenic. In addition, paternal arsenic exposure induced transgenerational effects of learning and memory disorder in F2 male rats through the regulation of H3K4me2 and H3K9me1/2/3, which inhibited c-Fos, mGlur1, and Nmdar1 expression. These results provide novel insights into the molecular mechanism of arsenic-induced neurotoxicity and highlight the risk of neurological deficits in offspring with paternal exposure to arsenic.

Soil redox status governs within-field spatial variation in microbial arsenic methylation and rice straighthead disease.

Microbial arsenic (As) methylation in paddy soil produces mainly dimethylarsenate (DMA), which can cause physiological straighthead disease in rice. The disease is often highly patchy in the field, but the reasons remain unknown. We investigated within-field spatial variations in straighthead disease severity, As species in rice husks and in soil porewater, microbial composition and abundance of arsM gene encoding arsenite S-adenosylmethionine methyltransferase in two paddy fields. The spatial pattern of disease severity matched those of soil redox potential, arsM gene abundance, porewater DMA concentration, and husk DMA concentration in both fields. Structural equation modelling identified soil redox potential as the key factor affecting arsM gene abundance, consequently impacting porewater DMA and husk DMA concentrations. Core amplicon variants that correlated positively with husk DMA concentration belonged mainly to the phyla of Chloroflexi, Bacillota, Acidobacteriota, Actinobacteriota, and Myxococcota. Meta-omics analyses of soil samples from the disease and non-disease patches identified 5129 arsM gene sequences, with 71% being transcribed. The arsM-carrying hosts were diverse and dominated by anaerobic bacteria. Between 96 and 115 arsM sequences were significantly more expressed in the soil samples from the disease than from the non-disease patch, which were distributed across 18 phyla, especially Acidobacteriota, Bacteroidota, Verrucomicrobiota, Chloroflexota, Pseudomonadota, and Actinomycetota. This study demonstrates that even a small variation in soil redox potential within the anoxic range can cause a large variation in the abundance of As-methylating microorganisms, thus resulting in within-field variation in rice straighthead disease. Raising soil redox potential could be an effective way to prevent straighthead disease.

Arsenic-methylating microbial community in sediment along the water flow is correlated with the distance to a low-temperature hot spring

Abstract Microbially mediated arsenic methylation, remains understudied in subgeothermal environments. This study aimed to investigate the activity and diversity of arsM-carrying microorganisms in sediment samples (termed YC1, YC2, and YC5) from a low-temperature hot spring. Microcosm assays revealed that only YC1 and YC2 exhibited limited As-methylating activities, generating a maximum of 2.3–3.5 μg/L methylarsenate (MMA) and 2.2–2.8 μg/L dimethylarsenate (DMA). The addition of lactate and arsenite significantly promoted these activities, increasing the concentrations to 26.1–184.0 μg/L MMA and 38.1–204.0 μg/L DMA. The arsM gene abundance also increased by 46–276%, indicating that lactate can activate arsenite methylation. YC1 and YC2, which were closer to the hot spring hole than YC5 was, had similar patterns, and shared a similar arsM community structure, dominated by Actinobacteriota, Firmicutes, and Proteobacteriota on days 7 and 21. In contrast, at YC5, the sampling site far from the spring hole, representatives of Acidobacteriota were dominant on day 7, whereas those of Actinobacteriota were prevalent on day 21. Acidobacteriota co-occurred with dimethylarsenate production, and Mycobacterium co-occurred with DMA demethylation. These findings suggested that the low-temperature arsenic hot spring possessed diverse arsenic-methylating species, whereas demethylating bacteria preferred to inhabit niches farther from the hot spring.