Biotransformation Of Arsenite Research Articles

Comment on “Arsenite biotransformation by Rhodococcus sp.: Characterization, optimization using response surface methodology and mechanistic studies”, Science of the Total Environment, 687, 577–589(2019)

Kumari et al. investigated the arsenic resistance and arsenic biotransforming ability in three bacterial species, mainly Rhodococcus sp.. But in the use of response surface methodology to optimize key parameters that affect the removal of arsenic, the effects of dissolved oxygen and the effect of HA addition on the adsorption or oxidation of arsenic by bacteria were ignored. We therefore recommend taking the impacts of the above-mentioned factors on the removal of arsenic into examination.

Arsenite biotransformation by Rhodococcus sp.: Characterization, optimization using response surface methodology and mechanistic studies

A large population of the world is under increased health risk due to consumption of arsenic contaminated groundwater. The present study investigates the arsenic resistance and arsenic biotransforming ability in three bacterial species, namely Bacillus arsenicus, Rhodococcus sp. and Alcaligenes faecalis for employing them in potential groundwater bioremediation programmes. The tolerance to pH levels for the 3 organisms are 6–9 for A. faecalis, 5–10 for Rhodococcus and 5–9 for B. arsenicus. The arsenic bio-oxidation capacity was qualitatively confirmed by using the silver nitrate method and all three bacteria were able to convert arsenite to arsenate. The arsenite tolerance capacity (MIC values) were found to be 3 mM, 7 mM and 12 mM for B. arsenicus, A. faecalis and Rhodococcus sp. respectively. The changes in cellular morphology of these strains under various arsenic stress conditions were studied using advanced cell imaging techniques such as scanning electron microscopy and Atomic Force Microscopy. Rhodococcus sp. emerged as a potential candidate for bioremediation application. A response surface methodology was employed to optimize key parameters affecting arsenic removal (pH, Iron (II) soluble, concentration of humic acid and initial arsenic concentration) and at optimized conditions, experimental runs demonstrated 48.34% removal of As (III) (initial concentration = 500 μg/L) in a duration of 6 h, with complete removal after 48 h. Evidences from this work indicate that arsenic removal occurs through bioaccumulation, biotransformation and biosorption. The present study makes the first attempt to investigate the arsenic removal capability of Rhodococcus sp. in synthetic groundwater by employing bacterial whole cell assays. This study also sheds light on the arsenic tolerance and detoxification mechanisms employed by these bacteria, knowledge of which could be crucial in the successful implementation of in-situ bioremediation programmes.

Arsenite biotransformation and bioaccumulation by Klebsiella pneumoniae strain SSSW7 possessing arsenite oxidase (aioA) gene.

Arsenite oxidizing Klebsiella pneumoniae strain SSSW7 isolated from shipyard waste Goa, India showed a minimum inhibitory concentration of 21mM in mineral salts medium. The strain possessed a small supercoiled plasmid and PCR amplification of arsenite oxidase gene (aioA) was observed on plasmid as well as chromosomal DNA. It was confirmed that arsenite oxidase enzyme was a periplasmic protein with a 47% increase in arsenite oxidase activity at 1mM sodium arsenite. Scanning electron microscopy coupled with electron dispersive X-ray spectroscopic (SEM-EDS) analysis of 15mM arsenite exposed cells revealed long chains of cells with no surface adsorption of arsenic. Transmission electron microscopy combined with electron dispersive X-ray spectroscopic (TEM-EDS) analysis demonstrated plasma membrane disruption, cytoplasmic condensation and periplasmic accumulation of arsenic. The bacterial strain oxidized 10mM of highly toxic arsenite to less toxic arsenate after 24h of incubation. Fourier transformed infrared (FTIR) spectroscopy confirmed the interaction of arsenite with functional groups present on the bacterial cell surface. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 5mM arsenite exposed cells demonstrated over-expression of 87kDa and 14kDa proteins of two subunits aioA and aioB of heterodimer arsenite oxidase enzyme as compared to control cells. Therefore, this bacterial strain might be employed as a potential candidate for bioremediation of arsenite contaminated environmental sites.

Assessment of arsenic oxidation potential of Microvirga indica S-MI1b sp. nov. in heavy metal polluted environment

Arsenic oxidizing α-proteobacterial strain Microvirga indica S-MI1b sp. nov. was isolated from metal industry soil and has the ability to oxidize 15 mM of arsenite [As(III)] completely in 39 h. The strain S-MI1b resists to different heavy metals and it oxidizes arsenite in presence of Li, Pb, Hg, Sb(III), Cd, Cr(VI), Ni, and exhibited growth inhibitory effect in presence of Hg, Cu, and Cd at higher concentration. The morphology of Microvirga indica S-MI1b changed in presence of heavy metals however there was no accumulation of As(III) in the cells. The study showed that Microvirga indica S-MI1b can oxidize arsenite at broad pH ranges from 4.0 to 9.0 with optimum at pH 7.0. The kinetic studies of arsenite oxidation by strain S-MI1b signified that it has greater affinity towards As(III). The arsenite oxidase activity of cells grown in presence of Li and Cr(VI) supported the cell culture studies. This is first report on biotransformation of arsenite by Microvirga genus and also arsenite oxidation in presence of heavy metals.

Isolation and identification of indigenous prokaryotic bacteria from arsenic-contaminated water resources and their impact on arsenic transformation

Arsenic is a known human carcinogen. Arsenite [As(III), H3AsO3] and arsenate [As(V), H2AsO4- and HAsO42-] are the two predominant compounds of As found in surface water and groundwater. The aim of this study was to explore a bioremediation strategy for biotransformation of arsenite to arsenate by microorganisms. In this study, Babagorgor Spring, located west of Iran, was selected as the arsenic-contaminated source and its physicochemical characteristics and in situ microbiological composition were analyzed. Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) analysis indicated that the arsenic level was 614μg/l. Fourteen arsenic tolerant indigenous bacteria were isolated from arsenic-contaminated water using chemically defined medium (CDM), supplemented with 260–3900mg/l arsenite and 1560–21800mg/l arsenate. Among the isolates, a strain As-11 exhibited high ability of arsenic transformation. Biochemical tests were used for bacterial identification and confirmation was conducted by 16S rRNA sequence analysis. Results confirmed that As-11 was related to the genus Pseudomonas. This bacterium showed maximum tolerable concentration to arsenite up to 3250mg/l and arsenate up to 20280mg/l. Under heterotrophic conditions, the bacterium exhibited 48% of As(III) and 78% of As(V) transformation from the medium amended with 130 and 312mg/l of sodium arsenite and sodium arsenate, respectively. Moreover, under chemolithotrophic conditions, bacterium was able to transform 41% of 130mg/l of As(III) from the medium amended with nitrate as the terminal electron acceptor. Pseudomonas strain As-11 was reported as an arsenic transformer, for the first time.

Isolation of Arsenic Resistant Escherichia coli from Sewage Water and Its Potential in Arsenic Biotransformation

Arsenic contamination in drinking water from ground water poses a threat to the health of a large population in developing countries in Asia. This has sparked great interests in the potential of different microbes in arsenic resistance and removal from water. This study involves isolation of arsenic resistant Escherichia coli from sewage water from Kathmandu University and investigation of its attributes. Arsenic resistant E. coli was successfully isolated which could survive in high concentration of arsenic. The maximum tolerance of arsenite was 909.79 mg/L (sodium arsenite) and 3120.1 mg/L arsenate (sodium arsenate) which is well above most natural concentration of arsenic in ground water. This particular E. coli tolerated multiple heavy metal like silver nitrate, cobalt sulphate, cadmium chloride, nickel chloride, mercury chloride, copper sulphate, and zinc chloride at concentration 20 µM, 1 mM, 0.5mM, 1mM, 0.01 mM, 1 mM, and 1 mM respectively which are concentrations known to be toxic to E. coli. Biotransformation of arsenite to arsenate was also checked for by a qualitative silver nitrate technique. This E. coli was able to transform arsenate to arsenite. It showed some sensitivity to Ciprofloxacin, Gentamicin and Nalidixic Acid. As E. coli and its genome are very widely studied, these particular properties have a lot of potential in microbial remediation or microbial recovery of metals and possible recombination approaches.

Biotransformation of arsenite and bacterial aox activity in drinking water produced from surface water of floating houses: Arsenic contamination in Cambodia

The potential arsenite bioteansformation activity of arsenic was investigated by examining bacterial arsenic arsenite-oxidizing gene such as aoxS, aoxR, aoxA, aoxB, aoxC, and aoxD in high arsenic-contaminated drinking water produced from the surface water of floating houses. There is a biogeochemical cycle of activity involving arsenite oxidase aox system and the ars (arsenic resistance system) gene operon and aoxR leader gene activity in Alcaligenes faecalis SRR-11 and aoxS leader gene activity in Achromobacter xylosoxidans TSL-66. Batch experiments showed that SRR-11 and TSL-66 completely oxidized 1 mM of As (III) to As (V) within 35–40 h. The leaders of aoxS and aoxR are important for gene activity, and their effects in arsenic bioremediation and mobility in natural water has a significant ecological role because it allows arsenite oxidase in bacteria to control the biogeochemical cycle of arsenic-contaminated drinking water produced from surface water of floating houses.

Mathematical model of uptake and metabolism of arsenic(III) in human hepatocytes - Incorporation of cellular antioxidant response and threshold-dependent behavior

BackgroundArsenic is an environmental pollutant, potent human toxicant, and oxidative stress agent with a multiplicity of health effects associated with both acute and chronic exposures. A semi-mechanistic cellular-level toxicokinetic (TK) model was developed in order to describe the uptake, biotransformation and clearance of arsenical species in human hepatocytes. Notable features of this model are the incorporation of arsenic-glutathione complex formation and a "switch-like" formulation to describe the antioxidant response of hepatocytes to arsenic exposure.ResultsThe cellular-level TK model applies mass action kinetics in order to predict the concentrations of trivalent and pentavalent arsenicals in hepatocytes. The model simulates uptake of arsenite (iAsIII) via aquaporin isozymes 9 (AQP9s), glutathione (GSH) conjugation, methylation by arsenic methyltransferase (AS3MT), efflux through multidrug resistant proteins (MRPs) and the induced antioxidant response via thioredoxin reductase (TR) activity. The model was parameterized by optimization of model estimates for arsenite (iAsIII), monomethylated (MMA) and dimethylated (DMA) arsenicals concentrations with time-course experimental data in human hepatocytes for a time span of 48 hours, and dose-response data at 24 hours for a range of arsenite concentrations from 0.1 to 10 μM. Global sensitivity analysis of the model showed that at low doses the transport parameters had a dominant role, whereas at higher doses the biotransformation parameters were the most significant. A parametric comparison of the TK model with an analogous model developed for rat hepatocytes from the literature demonstrated that the biotransformation of arsenite (e.g. GSH conjugation) has a large role in explaining the variation in methylation between rats and humans.ConclusionsThe cellular-level TK model captures the temporal modes of arsenical accumulation in human hepatocytes. It highlighted the key biological processes that influence arsenic metabolism by explicitly modelling the metabolic network of GSH-adducts formation. The parametric comparison with the TK model developed for rats suggests that the variability in GSH conjugation could have an important role in inter-species variability of arsenical methylation. The TK model can be incorporated into larger-scale physiologically based toxicokinetic (PBTK) models of arsenic for improving the estimates of PBTK model parameters.

Dose-dependent biotransformation of arsenite in rats—not S-adenosylmethionine depletion impairs arsenic methylation at high dose

Arsenite (AsIII) is eliminated via excretion and methylation. Monomethylarsonous acid (MMAsIII) is a super toxic metabolite of AsIII, while dimethylarsinic acid produced in the next metabolic step is relatively atoxic. Since the role of methylation in the acute toxicity and elimination of AsIII in vivo is unclear, we have examined the excretion and tissue retention of AsIII and its metabolites in rats exposed to increasing AsIII doses. Rats were injected i.v. with 20, 50 and 125 μmol/kg AsIII and arsenic metabolites in bile, urine and tissues were analysed. The excretion of AsIII increased almost proportionately to the dose, while its concentration in tissues rose more than proportionately. In contrast, the excretion and tissue concentrations of methylated metabolites increased less than the dosage, or they even decreased after injection of the largest dose of AsIII. To elucidate the mechanism of the dose-dependent decrease of methylation, we quantified S-adenosylmethionine (SAME), glutathione (GSH), and adenine nucleotides in the liver of AsIII-injected rats. AsIII decreased the hepatic concentrations of GSH and adenosine 5′-triphosphate (ATP) and the energy charge in a dose-dependent manner, but increased the level of SAME. Thus, impaired methylation after AsIII overdose is not due to SAME shortage, but probably to methyltransferase inhibition. It appears that exhausted elimination capacity of AsIII, rather than MMAsIII produced from AsIII, contributes significantly to the acute toxicity of AsIII. After GSH depletion the retained AsIII can increasingly inhibit SH-enzymes, thus causing ATP depletion and energetic disorder.

Biotransformation of arsenite in freshwater food‐chain models

AbstractBioaccumulation and biotransformation of arsenite by freshwater organisms consisting Daphnia magna, Neocaridina denticulata and Tilapia mossambica has been studied. When organisms were exposed to a medium containing arsenite, the total arsenic concentration accumulated by the organisms increased with an increase in the arsenic concentration in the medium. The order of total arsenic accumulation by freshwater organisms was D. magna > N. denticulata > T. mossambica. Bioaccumulation and biotransformation of arsenite in three‐step laboratory food‐chain models was investigated by feeding a diet of arsenite‐dosed alga (Chlorella vulgaris) to herbivorous grazers (D. magna and N. denticulata) and then the herbivores were fed to carnivorous fish (T. mossambica and Zacco platypus). Total arsenic concentrations in the organisms decreased by an order of magnitude for each step in the food chain. Arsenite and arsenate were accumulated as the predominant arsenic species in organisms. Little methylation of arsenic in organisms occurred at each step in the food chain. Copyright © 2001 John Wiley & Sons, Ltd.

Enzymatic reduction of arsenic compounds in mammalian systems: the rate-limiting enzyme of rabbit liver arsenic biotransformation is MMA(V) reductase.

A unique enzyme, MMA(V) reductase, has been partially purified from rabbit liver by using DEAE-cellulose, carboxymethylcellulose, and red dye ligand chromatography. The enzyme is unique since it is the rate-limiting enzyme in the biotransformation of inorganic arsenite in rabbit liver. The K(m) and V(max) values were 2.16 x 10(-)(3) M and 10.3 micromol h(-)(1) (mg of protein)(-)(1). When DMA(V) or arsenate was tested as a substrate, the K(m) was 20.9 x 10(-)(3) or 109 x 10(-)(3) M, respectively. The enzyme has an absolute requirement for GSH. Other thiols such as DTT or L-cysteine were inactive alone. At a pH below the physiological pH, GSH carried out this reduction, but this GSH reduction in the absence of the enzyme had little if any value at pH 7.4. When the K(m) values of rabbit liver arsenite methyltransferase (5.5 x 10(-)(6) M) and MMA(III) methyltransferase (9.2 x 10(-)(6)) were compared to that of MMA(V) reductase (2.16 x 10(-)(3) M), it can be concluded that MMA(V) reductase was the rate-limiting enzyme of inorganic arsenite biotransformation. MMA(V) reductase was also present in surgically removed human liver.

Enzymatic Methylation of Arsenic Compounds: V. Arsenite Methyltransferase Activity in Tissues of Mice

With the development of a rapid assay for arsenite methyltransferase (Zakharyanet al.,1995), the specific activity of this critical enzyme for arsenite biotransformation was determined by incubating liver, testis, kidney, or lung cytosol of male B6C3F1 mice with sodium arsenite andS-[methyl-3H]adenosyl-l-methionine and measuring the formation of [methyl-3H]monomethylarsonate. The mean arsenite methyltransferase specific activities (U/mg ± SEM) measured in these organs were liver, 0.40 ± 0.06; testis, 1.45 ± 0.08; kidney, 0.70 ± 0.06; and lung, 0.22 ± 0.01. Heretofore, the enzymatic methylation of arsenite has been regarded primarily as a hepatic function. The arsenite methyltransferase specific activity of the testis was 3.6 times greater than that of the liver (p< 0.01) and the specific activity of the kidney was 1.8 times greater than that of the liver (p< 0.05). Additionally, when mice were given arsenate in drinking water for 32 or 91 days at concentrations of 25 or 2500 μg As/L, the arsenite methyltransferase activities of liver, testis, kidney, and lung cytosol were not significantly increased in animals receiving either dose of arsenic for either 32 or 91 days compared to controls. No evidence for the induction of arsenite methyltransferase was found under these experimental conditions.

Effects of low dietary intake of methionine, choline or proteins on the biotransformation of arsenite in the rabbit

The effects of 6 weeks feeding with diets low in methionine, choline, or proteins on the biotransforma- tion and retention of 76As-labelled arsenite (0.4 mg As/kg bw) in rabbits have been studied. All test diets caused a significant decrease in the urinary excretion of dimethyl[ 76As]-arsinic acid, the main metabolite of inorganic arsenic. This gave rise to an increased retention of arsenic in the tissues, especially liver and lung. The test diets also caused a specific increase of the arsenic concentration in liver microsomes. The results indicate that subjects with a poor nutritional status have a lower capacity of methylating and thereby detoxifying inorganic arsenic.

Dimercaptan metal-binding agents influence the biotransformation of arsenite in the rabbit

The urinary metabolites of sodium arsenite have been investigated in rabbits given sodium arsenite and water-soluble dimercaptans. Rabbits injected sc with NaAsO 2 (1 mg As/kg) were given, im 1 hr later, either saline, 2,3-dimercapto-1-propanesulfonic acid (DMPS), meso-dimercaptosuccinic acid (DMSA), or N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) at 0.2 mmol/kg. Arsenic metabolites in urine collected from treated rabbits were isolated by combined anion-cation-exchange chromatography. Column fractions were acid-digested and analyzed for arsenic by direct hydride-flame atomic absorption spectrophotometry. The relative amounts of inorganic arsenic, methylarsonate, and dimethylarsinate found in 0 to 24 hr urine of rabbits given only sodium arsenite agreed closely with those reported for human subjects given arsenite po. This finding suggests that the rabbit biotransforms arsenite in a manner very similar to that of man. The urinary excretion of total arsenic between 0 and 24 hr was elevated after dimercaptan administration, but urinary excretion of total arsenic between 0 and 48 hr was unaffected. This result indicates that the action of these dimercaptans occurs early after treatment. In addition, the dimercaptans influenced differently the amounts of the arsenic metabolites excreted in the urine between 0 and 24 hr. DMPS, DMSA, or DMPA increased arsenite excretion but decreased dimethylarsinate excretion. DMPS or DMPA treatment increased methylarsonate excretion but DMSA did not. Arsenate excretion increased after DMPS or DMSA treatment but was not affected by DMPA treatment. These results suggest that the dimercaptans, in addition to increasing arsenic excretion, also influence the biotransformation of arsenite to less toxic species. The different effects on the urinary excretion of arsenic metabolites suggest that these dimercaptan metal binding agents have mechanisms of action in addition to simple chelation of inorganic arsenic.

Intracellular interaction and biotransformation of arsenite in rats and rabbits

The accumulation of arsenic with time in tissues of rats and rabbits was determined by neutron activation analysis (NAA). Rats showed a steady increase in the As-concentrations with age, whereas in rabbits it was nearly the same for adults and in young animals. The metabolism of arsenic was studied in both animal species after i.p. injection of 50/μg As/kg b.w. as 74As labelled arsenite. Eight tissues, as well as blood and urine, were analysed for 74As content after 16 and 48 hours. The binding of 74As to hematic and intracellular components and the chemical forms of arsenic in tissues and urine were investigated. In the plasma and the RBC-fraction of the rabbit, the As concentration decreased during the first two days, while in the rats it only disappeared from the plasma, but was retained in the RBC-fraction. Liver, kidney and lung of rabbits with the highest As concentrations at 16 and 48 hours showed a rapid clearance of As in the first 48 hours. In the corresponding tissues of the rats, the rate of decline was significantly lower, due to the higher binding of 74As to tissue constituents. Poor binding of As to plasma proteins was seen in rabbits while in rats it was totally bound to this fraction. In the RBC, liver and kidney cytosols, however, the affinity of As for intracellular proteins was higher in both animal species but characterized by a rate of binding different between the two animal species. The amount of dimethylarsinic acid (DMA) in the tissues was significantly lower in the rat than in the rabbit, reflecting the total amount of diffusible arsenic, which was also much lower in the tissues of rats than in rabbits.