Metal-Binding Protein TaGlo1 Improves Fungal Resistance to Arsenite (AsIII) and Methylarsenite (MAsIII) in Paddy Soil.

Trivalent arsenicals such as arsenite (AsIII) and methylarsenite (MAsIII) are thought to be ubiquitous in flooded paddy soils and have higher toxicity than pentavalent forms. Fungi are widely prevalent in the rice rhizosphere, and the latter is considered a hotspot for As uptake. However, few studies have focused on alleviating As toxicity in paddy soils using fungi. In this study, we investigated the mechanism by which the protein TaGlo1, derived from the As-resistant fungal strain Trichoderma asperellum SM-12F1, mitigates AsIII and MAsIII toxicity in paddy soils. Taglo1 gene expression in Escherichia coli BL21 conferred strong resistance to AsIII and MAsIII, while purified TaGlo1 showed a high affinity for AsIII and MAsIII. Three cysteine residues (Cys13, Cys18, and Cys71) play crucial roles in binding with AsIII, while only two (Cys13 and Cys18) play crucial roles for MAsIII binding. TaGlo1 had a stronger binding strength for MAsIII than AsIII. Importantly, up to 90.2% of the homologous TaGlo1 proteins originate from fungi by GenBank searching. In the rhizospheres of 14 Chinese paddy soils, Taglo1 was widely distributed and its gene abundance increased with porewater As. This study highlights the potential of fungi to mitigate As toxicity and availability in the soil-rice continuum and suggests future microbial strategies for bioremediation.

Chronic Exposure to Drinking Water As, Pb, and Cd at Provisional Guideline Values Reduces Weight Gain in Male Mice via Gut Microflora Alterations and Intestinal Inflammation.

Few studies have investigated the long-term effect of exposure to arsenic (As), lead (Pb), and cadmium (Cd) via drinking water at the provisional guideline values on gut microflora. In this study, male and female mice were exposed to water As, Pb, or Cd at 10, 10, or 5 µg L-1 for 6 months. At the end of the exposure, the net weight gain of male mice exposed to As and Pb (9.91 ± 1.35 and 11.2 ± 1.50 g) was significantly (p < 0.05) lower compared to unexposed control mice (14.1 ± 3.24 g), while this was not observed for female mice. Relative abundance of Akkermansia, a protective gut bacterium against intestinal inflammation, was reduced from 29.7% to 3.20%, 4.83%, and 17.0% after As, Pb, and Cd exposure in male mice, which likely caused chronic intestinal inflammation, as suggested by 2.81- to 9.60-fold higher mRNA levels of pro-inflammatory factors in ileal enterocytes of male mice. These results indicate that long-term exposure to drinking water As, Pb, and Cd at concentrations equivalent to the China provisional guideline values can cause loss of protective bacteria and lead to chronic intestinal inflammation, thereby affecting body weight gain in male mice.

Gut Microbiota Control the Bioavailability and Metabolism of Organoarsenicals of Seaweeds in Mice after Oral Ingestion.

Edible seaweed consumption is an essential route of human exposure to complex organoarsenicals, including arsenosugars and arsenosugar phospholipids. However, the effects of gut microbiota on the metabolism and bioavailability of arsenosugars in vivo are unknown. Herein, two nori and two kelp samples with phosphate arsenosugar and sulfonate arsenosugar, respectively, as the predominant arsenic species, were administered to normal mice and gut microbiota-disrupted mice treated with the broad-spectrum antibiotic cefoperazone for 4 weeks. Following exposure, the community structures of the gut microbiota, total arsenic concentrations, and arsenic species in excreta and tissues were analyzed. Total arsenic excreted in feces and urine did not differ significantly between normal and antibiotic-treated mice fed with kelp samples. However, the total urinary arsenic of normal mice fed with nori samples was significantly higher (p < 0.05) (urinary arsenic excretion factor, 34-38 vs 5-7%), and the fecal total arsenic was significantly lower than in antibiotic-treated mice. Arsenic speciation analysis revealed that most phosphate arsenosugars in nori were converted to arsenobetaine (53.5-74.5%) when passing through the gastrointestinal tract, whereas a large portion of sulfonate arsenosugar in kelp was resistant to speciation changes and was excreted in feces intact (64.1-64.5%). Normal mice exhibited greater oral bioavailability of phosphate arsenosugar from nori than sulfonate arsenosugar from kelp (34-38 vs 6-9%). Our work provides insights into organoarsenical metabolism and their bioavailability in the mammalian gut.

Identification and characterization of a phosphinothricin N-acetyltransferase from Enterobacter LSJC7.

Phosphinothricin (PPT) is a widely used and non-selective herbicide. PPT-resistance genes, especially PPT N-acetyltransferase genes, have been used in the development of transgenic PPT-resistant crops. However, there are only a limited number of available PPT-resistance genes for use in plant biotechnology. In this study, we found that Enterobacter LSJC7 is highly resistant to PPT and can acetylate PPT to N-acetyl phosphinothricin (Ac-PPT). Furthermore, a novel PPT N-acetyltransferase gene, named LsarsN, was identified from LSJC7. When LsarsN was expressed in E. coli AW3110, it confered resistance to PPT. Ac-PPT was detected in both the culture medium and cells of AW3110 expressing the LsarsN-pET22b plasmid. The purified LsArsN protein also showed strong N-acetylation ability in vitro, and its enzymatic kinetic curve was fitted with the Michaelis-Mentan equation. Compared with wild-type LsArsN, both R72A and R74A mutants showed significantly lower PPT N-acetylation ability. In summary, our results systematically characterized LsArsN with strong ability for PPT N-acetylation, which lays the groundwork for future research into the use of this novel gene, LsarsN, to create PPT-resistant crops.

Stimulation of N2 O emission via bacterial denitrification driven by acidification in estuarine sediments.

Ocean acidification in nitrogen-enriched estuaries has raised global concerns. For decades, biotic and abiotic denitrification in estuarine sediments has been regarded as the major ways to remove reactive nitrogen, but they occur at the expense of releasing greenhouse gas nitrous oxide (N2 O). However, how these pathways respond to acidification remains poorly understood. Here we performed a N2 O isotopocules analysis coupled with respiration inhibition and molecular approaches to investigate the impacts of acidification on bacterial, fungal, and chemo-denitrification, as well as N2 O emission, in estuarine sediments through a series of anoxic incubations. Results showed that acidification stimulated N2 O release from sediments, which was mainly mediated by the activity of bacterial denitrifiers, whereas in neutral environments, N2 O production was dominated by fungi. We also found that the contribution of chemo-denitrification to N2 O production cannot be ignored, but was not significantly affected by acidification. The mechanistic investigation further demonstrated that acidification changed the keystone taxa of sedimentary denitrifiers from N2 O-reducing to N2 O-producing ones and reduced microbial electron-transfer efficiency during denitrification. These findings provide novel insights into how acidification stimulates N2 O emission and modulates its pathways in estuarine sediments, and how it may contribute to the acceleration of global climate change in the Anthropocene.

Effects of Arsenic on Gut Microbiota and Its Biotransformation Genes in Earthworm Metaphire sieboldi.

Arsenic biotransformation mediated by gut microbiota can affect arsenic bioavailability and microbial community. Arsenic species, arsenic biotransformation genes (ABGs), and the composition of gut microbial community were characterized after the earthworm Metaphire sieboldi was cultured in soils spiked with different arsenic concentrations. Arsenite (As(III)) was the major component in the earthworm gut, whereas arsenate (As(V)) was predominant in the soil. A total of 16 ABGs were quantified by high-throughput quantitative polymerase chain reaction (HT-qPCR). Genes involved in arsenic redox and efflux were predominant in all samples, and the abundance of ABGs involved in arsenic methylation and demethylation in the gut was very low. These results reveal that the earthworm gut can be a reservoir of microbes with the capability of reducing As(V) and extruding As(III) but with little methylation of arsenic. Moreover, gut microbial communities were dominated by Actinobacteria, Firmicutes, and Proteobacteria at the phylum level and were considerably different from those in the surrounding soil. Our work demonstrates that exposure to As(V) disturbs the gut microbiota of earthworms and provides some insights into arsenic biotransformation in the earthworm gut.

Identification of Steps in the Pathway of Arsenosugar Biosynthesis.

Arsenosugars are arsenic-containing ribosides that play a substantial role in arsenic biogeochemical cycles. Arsenosugars were identified more than 30 years ago, and yet their mechanism of biosynthesis remains unknown. In this study we report identification of the arsS gene from the cyanobacterium Synechocystis sp. PCC 6803 and show that it is involved in arsenosugar biosynthesis. In the Synechocystis sp. PCC 6803 ars operon, arsS is adjacent to the arsM gene that encodes an As(III) S-adenosylmethionine (SAM) methyltransferase. The gene product, ArsS, contains a characteristic CX3CX2C motif which is typical for the radical SAM superfamily. The function of ArsS was identified from a combination of arsS disruption in Synechocystis sp. PCC 6803 and heterologous expression of arsM and arsS in Escherichia coli. Both genes are necessary, indicating a multistep pathway of arsenosugar biosynthesis. In addition, we demonstrate that ArsS orthologs from three other freshwater cyanobacteria and one picocyanobacterium are involved in arsenosugar biosynthesis in those microbes. This study represents the identification of the first two steps in the pathway of arsenosugar biosynthesis. Our discovery expands the catalytic repertoire of the diverse radical SAM enzyme superfamily and provides a basis for studying the biogeochemistry of complex organoarsenicals.

Arsenic and Sulfamethoxazole Increase the Incidence of Antibiotic Resistance Genes in the Gut of Earthworm.

Combinations of metal(loid) contamination and antibiotics are considered to increase the abundance of resistance genes in the environment, whereas the combined effect of metal(loid)s and antibiotics on microbial communities and antibiotic resistance genes (ARGs) in the gut of soil fauna remains unknown. We investigated herein the alteration of ARGs and the gut microbial communities after the earthworm Metaphire sieboldi was exposed to arsenate and/or sulfamethoxazole using high-throughput quantitative PCR and Illumina sequencing analysis. Arsenic accumulation in the body tissues of arsenic-exposed earthworms exerted a significant inhibition on growth and survival. The synergistic interactions of arsenic and sulfamethoxazole increased significantly the incidence of ARGs and mobile genetic elements in the earthworm gut microbiota. In addition, co-exposure to arsenic and sulfamethoxazole altered the structure of the gut microbial communities, and the changes correlated with ARG profiles of the gut microbiota. Our results indicate that the gut of soil fauna is a neglected hotspot of antibiotic resistance.

Enhanced antibacterial activity of silver-decorated sandwich-like mesoporous silica/reduced graphene oxide nanosheets through photothermal effect.

Drug resistance of bacteria has become a global health problem, as it makes conventional antibiotics less efficient. It is urgently needed to explore novel antibacterial materials and develop effective treatment strategies to overcome the drug resistance of antibiotics. Herein, we successfully synthesized silver decorated sandwich-like mesoporous silica/reduced graphene oxide nanosheets (rGO/MSN/Ag) as a novel antibacterial material through facile method. The rGO and Ag nanoparticles can be reduced in the reaction system without adding any other reductants. In addition, the rGO/MSN/Ag showed higher photothermal conversion capacity due to the modification of silver nanoparticles and exhibited excellent antibacterial activities against Pseudomonas putida, Escherichia coli and Rhodococcus at relatively low dosages, which was confirmed by the minimum inhibitory concentration (MIC) test. Meanwhile, the E. coli with a high concentration was selected for exposure using an 808 nm laser, and the antibacterial effect was obviously enhanced by the near-infrared irradiation induced photothermal effect. Moreover, the hepatocyte LO2 were used for the cytotoxicity evaluation, and the rGO/MSN/Ag showed low toxicity and were without detectable cytotoxicity at the antimicrobial dose. As the prepared rGO/MSN/Ag nanosheets have the advantages of low-cost and high antibacterial activity, they might be of promising and useful antibacterial agents for different applications.

Linking Genes to Microbial Biogeochemical Cycling: Lessons from Arsenic.

The biotransformation of arsenic is highly relevant to the arsenic biogeochemical cycle. Identification of the molecular details of microbial pathways of arsenic biotransformation coupled with analyses of microbial communities by meta-omics can provide insights into detailed aspects of the complexities of this biocycle. Arsenic transformations couple to other biogeochemical cycles, and to the fate of both nutrients and other toxic environmental contaminants. Microbial redox metabolism of iron, carbon, sulfur, and nitrogen affects the redox and bioavailability of arsenic species. In this critical review we illustrate the biogeochemical processes and genes involved in arsenic biotransformations. We discuss how current and future metagenomic-, metatranscriptomic-, metaproteomic-, and metabolomic-based methods will help to decipher individual microbial arsenic transformation processes, and their connections to other biogeochemical cycle. These insights will allow future use of microbial metabolic capabilities for new biotechnological solutions to environmental problems. To understand the complex nature of inorganic and organic arsenic species and the fate of environmental arsenic will require integrating systematic approaches with biogeochemical modeling. Finally, from the lessons learned from these studies of arsenic biogeochemistry, we will be able to predict how the environment changes arsenic, and, in response, how arsenic biotransformations change the environment.

Arsenic Methyltransferase is Involved in Arsenosugar Biosynthesis by Providing DMA.

Arsenic is an ubiquitous toxic element in the environment, and organisms have evolved different arsenic detoxification strategies. Studies on arsenic biotransformation mechanisms have mainly focused on arsenate (As(V)) reduction, arsenite (As(III)) oxidation, and arsenic methylation; little is known, however, about the pathway for the biosynthesis of arsenosugars, which are significant arsenic transformation products. Here, the involvement of As(III) S-Adenosylmethionine methyltransferase (ArsM) in arsenosugar synthesis is demonstrated for the first time. Synechocystis sp. PCC 6803 incubated with As(III) or monomethylarsonic acid (MMA(V)) produced dimethylarsinic acid (DMA(V)) and arsenosugars, as determined by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC/ICPMS). Arsenosugars were also detected in the cells when they were exposed to DMA(V). A mutant strain Synechocystis ΔarsM was constructed by disrupting arsM in Synechocystis sp. PCC 6803. Methylation of arsenic species was not observed in the mutant strain after exposure to arsenite or MMA(V); when Synechocystis ΔarsM was incubated with DMA(V), arsenosugars were detected in the cells. These results suggest that ArsM is a required enzyme for the methylation of inorganic arsenicals, but not required for the synthesis of arsenosugars from DMA, and that DMA is the precursor of arsenosugar biosynthesis. The findings will stimulate more studies on the biosynthesis of complex organoarsenicals, and lead to a better understanding of the bioavailability and function of the organoarsenicals in biological systems.

Arsenic methylation by an arsenite S-adenosylmethionine methyltransferase from Spirulina platensis.

Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation. Spirulina platensis (S. platensis), a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite (As(III)), S. platensis accumulated arsenic up to 4.1mg/kg dry weight. After exposure to As(III), arsenate (As(V)) was the predominant species making up 64% to 86% of the total arsenic. Monomethylarsenate (MMA(V)) and dimethylarsenate (DMA(V)) were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis (SpArsM) was identified and characterized. SpArsM showed low identity with other reported ArsM enzymes. The Escherichia coli AW3110 bearing SparsM gene resulted in As(III) methylation and conferring resistance to As(III). The in vitro assay showed that SpArsM exhibited As(III) methylation activity. DMA(V) and a small amount of MMA(V) were detected in the reaction system within 0.5hr. A truncated SpArsM derivative lacking the last 34 residues still had the ability to methylate As(III). The three single mutants of SpArsM (C59S, C186S, and C238S) abolished the capability of As(III) methylation, suggesting the three cysteine residues are involved in catalysis. We propose that SpArsM is responsible for As methylation and detoxification of As(III) and may contribute to As biogeochemistry.

Arsenic Demethylation by a C·As Lyase in Cyanobacterium Nostoc sp. PCC 7120.

Arsenic, a ubiquitous toxic substance, exists mainly as inorganic forms in the environment. It is perceived that organoarsenicals can be demethylated and degraded into inorganic arsenic by microorganisms. Few studies have focused on the mechanism of arsenic demethylation in bacteria. Here, we investigated arsenic demethylation in a typical freshwater cyanobacterium Nostoc sp. PCC 7120. This bacterium was able to demethylate monomethylarsenite [MAs(III)] rapidly to arsenite [As(III)] and also had the ability to demethylate monomethylarsenate [MAs(V)] to As(III). The NsarsI encoding a C·As lyase responsible for MAs(III) demethylation was cloned from Nostoc sp. PCC 7120 and heterologously expressed in an As-hypersensitive strain Escherichia coli AW3110 (ΔarsRBC). Expression of NsarsI was shown to confer MAs(III) resistance through arsenic demethylation. The purified NsArsI was further identified and functionally characterized in vitro. NsArsI existed mainly as the trimeric state, and the kinetic data were well-fit to the Hill equation with K0.5 = 7.55 ± 0.33 µM for MAs(III), Vmax = 0.79 ± 0.02 µM min(-1), and h = 2.7. Both of the NsArsI truncated derivatives lacking the C-terminal 10 residues (ArsI10) or 23 residues (ArsI23) had a reduced ability of MAs(III) demethylation. These results provide new insights for understanding the important role of cyanobacteria in arsenic biogeochemical cycling in the environment.

Migration of phosphorus in pig manure during pyrolysis process and slow-release mechanism of biochar in hydroponic application.

Pyrolysis is an effective method for treating of livestock and poultry manure developed in recent years. It can completely decompose pathogens and antibiotics, stabilize heavy metals, and enrich phosphorus (P) in biochar. To elucidate the P migration mechanism under different pig manure pyrolysis temperatures, sequential fractionation, solution 31P nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, and K-edge X-ray absorption near-edge structure techniques were used to analyze the P species in pig manure biochar (PMB). The results indicated that most of the organic P in the pig manure was converted to inorganic P during pyrolysis. Moreover, the transformation to different P groups pathways was clarified. The phase transition from amorphous to crystalline calcium phosphate was promoted when the temperature was above 600 °C. The content of P extracted by hydrochloric acid, which was the long-term available P for plant uptake, increased significantly. PMB pyrolyzed at 600 °C can be used as a highly effective substitute for P source. It provides the necessary P species (e.g. water-soluble P.) and metal elements for the growth of water spinach plants, and which are slow-release comparing with the Hogland nutrient solution.

Interaction of tetracycline and copper co-intake in inducing antibiotic resistance genes and potential pathogens in mouse gut.

The widespread use of copper and tetracycline as growth promoters in the breeding industry poses a potential threat to environmental health. Nevertheless, to the best of our knowledge, the potential adverse effects of copper and tetracycline on the gut microbiota remain unknown. Herein, mice were fed different concentrations of copper and/or tetracycline for 6 weeks to simulate real life-like exposure in the breeding industry. Following the exposure, antibiotic resistance genes (ARGs), potential pathogens, and other pathogenic factors were analyzed in mouse feces. The co-exposure of copper with tetracycline significantly increased the abundance of ARGs and enriched more potential pathogens in the gut of the co-treated mice. Copper and/or tetracycline exposure increased the abundance of bacteria carrying either ARGs, metal resistance genes, or virulence factors, contributing to the widespread dissemination of potentially harmful genes posing a severe risk to public health. Our study provides insights into the effects of copper and tetracycline exposure on the gut resistome and potential pathogens, and our findings can help reduce the risks associated with antibiotic resistance under the One Health framework.

Ca Minerals and Oral Bioavailability of Pb, Cd, and As from Indoor Dust in Mice: Mechanisms and Health Implications.

BACKGROUND: Elevating dietary calcium (Ca) intake can reduce metal(loid)oral bioavailability. However, the ability of a range of Ca minerals to reduce oral bioavailability of lead (Pb), cadmium (Cd), and arsenic (As) from indoor dust remains unclear. OBJECTIVES: This study evaluated the ability of Ca minerals to reduce Pb, Cd, and As oral bioavailability from indoor dust and associated mechanisms. METHODS: A mouse bioassay was conducted to assess Pb, Cd, and As relative bioavailability (RBA) in three indoor dust samples, which were amended into mouse chow without and with addition of CaHPO4, CaCO3, Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate at 200-5,000µg/g Ca. The mRNA expression of Ca and phosphate (P) transporters involved in transcellular Pb, Cd and As transport in the duodenum of mice was quantified using real-time polymerase chain reaction. Serum 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], parathyroid hormone (PTH), and renal CYP27B1 activity controlling 1,25(OH)2D3 synthesis were measured using ELISA kits. Metal(loid) speciation in the feces of mice was characterized using X-ray absorption near-edge structure (XANES) spectroscopy. RESULTS: In general, mice exposed to each of the Ca minerals exhibited lower Pb-, Cd-, and As-RBA for three dusts. However, RBAs with the different Ca minerals varied. Among minerals, mice fed dietary CaHPO4 did not exhibit lower duodenal mRNA expression of Ca transporters but did have the lowest Pb and Cd oral bioavailability at the highest Ca concentration (5,000µg/g Ca; 51%-95% and 52%-74% lower in comparison with the control). Lead phosphate precipitates (e.g., chloropyromorphite) were observed in feces of mice fed dietary CaHPO4. In comparison, mice fed organic Ca minerals (Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate) had lower duodenal mRNA expression of Ca transporters, but Pb and Cd oral bioavailability was higher than in mice fed CaHPO4. In terms of As, mice fed Ca aspartate exhibited the lowest As oral bioavailability at the highest Ca concentration (5,000µg/g Ca; 41%-72% lower) and the lowest duodenal expression of P transporter (88% lower). The presence of aspartate was not associated with higher As solubility in the intestine. DISCUSSION: Our study used a mouse model of exposure to household dust with various concentrations and species of Ca to determine whether different Ca minerals can reduce bioavailability of Pb, Cd, and As in mice and elucidate the mechanism(s) involved. This study can contribute to the practical application of optimal Ca minerals to protect humans from Pb, Cd, and As coexposure in the environment. https://doi.org/10.1289/EHP11730.

Arsenic bioaccumulation in the soil fauna alters its gut microbiome and microbial arsenic biotransformation capacity.

The biotransformation of arsenic mediated by microorganisms plays an important role in the arsenic biogeochemical cycle. However, the fate and biotransformation of arsenic in different soil fauna gut microbiota are largely unknown. Herein the effects of arsenic contamination on five types of soil fauna were compared by examining variations in arsenic bioaccumulation, gut microbiota, and arsenic biotransformation genes (ABGs). Significant difference was observed in the arsenic bioaccumulation across several fauna body tissues, and Metaphire californica had the highest arsenic bioaccumulation, with a value of 107 ± 1.41 mg kg-1. Arsenic exposure significantly altered overall patterns of ABGs; however, dominant genes involved in arsenic redox and other genes involved in arsenic methylation and demethylation were not significantly changed across animals. Except for M. californica, the abundance of ABGs in other animal guts firstly increased and then decreased with increasing arsenic concentrations. In addition, exposure of soil fauna to arsenic led to shifts in the unique gut-associated bacterial community, but the magnitude of these changes varied significantly across ecological groups of soil fauna. A good correlation between the gut bacterial communities and ABG profiles was observed, suggesting that gut microbiota plays important roles in the biotransformation of arsenic. Overall, these results provide a universal profiling of a microbial community capable of arsenic biotransformation in different fauna guts. Considering the global distribution of soil fauna in the terrestrial ecosystem, this finding broadens our understanding of the hidden role of soil fauna in the arsenic bioaccumulation and biogeochemical cycle.

Antibiotic exposure decreases soil arsenic oral bioavailability in mice by disrupting ileal microbiota and metabolic profile.

Oral bioavailability of arsenic (As) determines levels of As exposure via ingestion of As-contaminated soil, however, the role of gut microbiota in As bioavailability has not evaluated in vivo although some in vitro studies have investigated this. Here, we made a comparison in As relative bioavailability (RBA) estimates for a contaminated soil (3913 mg As kg-1) using a mouse model with and without penicillin perturbing gut microbiota and metabolites. Compared to soil exposure alone (2% w/w soil in diets), addition of penicillin (100 or 1000 mg kg-1) reduced probiotic Lactobacillus and sulfate-reducing bacteria Desulfovibrio, enriched penicillin-resistant Enterobacter and Bacteroides, and decreased amino acid concentrations in ileum. With perturbed gut microbiota and metabolic profile, penicillin and soil co-exposed mice accumulated 2.81-3.81-fold less As in kidneys, excreted 1.02-1.35-fold less As in urine, and showed lower As-RBA (25.7-29.0%) compared to mice receiving diets amended with soil alone (56 ± 9.63%). One mechanism accounted for this is the decreased concentrations of amino acids arising from the gut microbiota shift which resulted in elevated iron (Fe) and As co-precipitation, leading to reduced As solubilization in the intestine. Another mechanism was conversion of bioavailable inorganic As to less bioavailable monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV) by the antibiotic perturbed microflora. Based on in vivo mouse model, we demonstrated the important role of gut microbiota and gut metabolites in participating soil As solubilization and speciation transformation then affecting As oral bioavailability. Results are useful to better understand the role of gut bacteria in affecting As metabolism and the health risks of As-contaminated soils.

The response of Pyropia haitanensis to inorganic arsenic under laboratory culture.

Up to now, complicated organoarsenicals were mainly identified in marine organisms, suggesting that these organisms play a critical role in arsenic biogeochemical cycling because of low phosphate and relatively high arsenic concentration in the marine environment. However, the response of marine macroalgae to inorganic arsenic remains unknown. In this study, Pyropia haitanensis were exposed to arsenate [As(V)] (0.1, 1, 10, 100 µM) or arsenite [As(III)] (0.1, 1, 10 µM) under laboratory conditions for 3 d. The species of water-soluble arsenic, the total concentration of lipid-soluble and cell residue arsenic of the algae cells was analyzed. As(V) was mainly transformed into oxo-arsenosugar-phosphate, with other arsenic compounds such as monomethylated, As(III), demethylated arsenic and oxo-arsenosugar-glycerol being likely the intermediates of arsenosugar synthesis. When high concentration of As(III) was toxic to P. haitanensis, As(III) entered into the cells and was transformed into less toxic organoarsenicals and As(V). Transcriptome results showed genes involved in DNA replication, mismatch repair, base excision repair, and nucleotide excision repair were up-regulated in the algae cells exposed to 10 µM As(V), and multiple genes involved in glutathione metabolism and photosynthetic were up-regulated by 1 µM As(III). A large number of ABC transporters were down-regulated by As(V) while ten genes related to ABC transporters were up-regulated by As(III), indicating that ABC transporters were involved in transporting As(III) to vacuoles in algae cells. These results indicated that P. haitanensis detoxifies inorganic arsenic via transforming them into organoarsenicals and enhancing the isolation of highly toxic As(III) in vacuoles.

ArsM-mediated arsenite volatilization is limited by efflux catalyzed by As efflux transporters.

Arsenic (As) methylation is regarded as an efficient strategy for As contamination remediation by As volatilization. However, most microorganisms display low As volatilization efficiency, which is possibly linked to As efflux transporters competing for cytoplasmic As(III) as a substrate. Here, we developed two types of As biosensors in Escherichia coli to compare the As efflux rate of three efflux transporters and to further investigate the correlation between As efflux rates and As volatilization. The engineered As-sensitive E. coli AW3110 expressing arsBRP, acr3RP or arsBEC displayed a higher As resistance compared to the control. The fluorescence intensity was in a linear correlation in the range of 0-2.0 µmol/L of As(III). The intracellular As(III) concentration was negatively related to As efflux activity of As efflux transporter, which was consistent with the As resistance assays. Moreover, arsM derived from R. palustris CGA009 was subsequently introduced to construct an E. coli AW3110 co-expressing arsB/acr3 and arsM, which exhibited higher As(III) resistance, lower fluorescence intensity and intracellular As concentration compared to the engineered E. coli AW3110 expressing only arsB/acr3. The As volatilization efficiency was negatively related to As efflux activity of efflux transporters, the recombinants without arsB/acr3 displayed the highest rate of As volatilization. This study provided new insights into parameters affecting As volatilization with As efflux being the main limiting factor for As methylation and subsequent volatilization in many microorganisms.