Bacterial Dissimilatory Reduction of Arsenic(V) to Arsenic(III) in Anoxic Sediments

Incubation of anoxic salt marsh sediment slurries with 10 mM As(V) resulted in the disappearance over time of the As(V) in conjunction with its recovery as As(III). No As(V) reduction to As(III) occurred in heat-sterilized or formalin-killed controls or in live sediments incubated in air. The rate of As(V) reduction in slurries was enhanced by addition of the electron donor lactate, H(inf2), or glucose, whereas the respiratory inhibitor/uncoupler dinitrophenol, rotenone, or 2-heptyl-4-hydroxyquinoline N-oxide blocked As(V) reduction. As(V) reduction was also inhibited by tungstate but not by molybdate, sulfate, or phosphate. Nitrate inhibited As(V) reduction by its action as a preferred respiratory electron acceptor rather than as a structural analog of As(V). Nitrate-respiring sediments could reduce As(V) to As(III) once all the nitrate was removed. Chloramphenicol blocked the reduction of As(V) to As(III) in nitrate-respiring sediments, suggesting that nitrate and arsenate were reduced by separate enzyme systems. Oxidation of [2-(sup14)C]acetate to (sup14)CO(inf2) by salt marsh and freshwater sediments was coupled to As(V). Collectively, these results show that reduction of As(V) in sediments proceeds by a dissimilatory process. Bacterial sulfate reduction was completely inhibited by As(V) as well as by As(III).     

Differential thiol status in blood of different mouse strains exposed to cigarette smoke

C57Bl/6J, DBA/2 and ICR mouse strains are known to possess different susceptibilities to developing emphysema after exposure to cigarette smoke with DBA/2 and C57Bl/6J strains being significantly more susceptible to pulmonary damage than the ICR strain. This study was aimed at analysing the occurrence of systemic oxidative stress in the blood of these different mouse strains after exposure to cigarette smoke. This study did not observe a significant decrease in glutathione in erythrocytes or in plasma cysteine, cysteinylglycine, homocysteine and glutathione in C57Bl/6J or DBA/2 mice, whereas a significant increase in the corresponding oxidized forms was observed in plasma. However, the ICR strain showed a significant increase in glutathione in erythrocytes and a significant decrease in most of the oxidized forms of cysteine, cysteinylglycine, homocysteine and glutathione in plasma after the same exposition. These experiments demonstrate that exposure to cigarette smoking induces systemic oxidative stress only in some mouse strains which are susceptible to developing emphysema.     

Toxicokinetics and Biotransformation of As(III) and As(V) in Eisenia fetida

Earthworms, Eisenia fetida, were exposed to soils spiked with As(III) and As(V), to understand the response of earthworms to As in terms of both toxicity and accumulation using toxicokinetics, and to explain As metabolism and bioavailability. As(III) showed higher toxicity than As(V), in all toxicity endpoints of burrowing time, survival, growth, and cocoon production. Bioconcentration occurred at both As(III) and As(V) treatments during 28-d exposure. Worms did not show the elimination of As for consecutive 28 d of exposure to clean soils. Biotransformation of As was characterized using HPLC-ICP-MS and XANES, showing the reduction of As in worms regardless of the As species to which worms were exposed. Metabolism of As in worms that formed As-thiol complex is thought to limit the excretion of As, and thus induce bioconcentration in worms. Uptake rates by one-compartment model indicated that pore water was the bioaccessible pool of As, and directly controlled the uptake of As by worms. The study suggests that higher uptake rate and bioaccumulation of As(III) than of As(V) are among the factors that make As(III) more toxic than As(V).     

Sulfur accumulation in western wheatgrass exposed to three controlled SO2 concentrations

Summary Sulfur concentrations of western wheatgrass tillers and individual leaves were measured from plants exposed to four SO₂ concentrations (9, 52, 105 and 183 g·m^–3). Sulfur concentration of plants was a linear function of either time of exposure or concentration.Young leaves and the youngest portion of leaves contained less sulfur than their older counterparts irregardless of whether they had or had not been exposed to SO₂.Current hypotheses which relate plant sensitivity to amount of sulfur taken up do not apply for western wheatgrass.     

Manganese (hyper)accumulation within Australian Denhamia (Celastraceae): an assessment of the trait and manganese accumulation under controlled conditions

Plant and Soil - The genus Denhamia(Celastraceae) includes fifteen Australian species, many of which have a propensity for manganese (Mn) (hyper)accumulation. Among the key aims of this study were...     

A Multi-biological Assay Approach to Assess Microbial Diversity in Arsenic (As) Contaminated Soils

Microbial genetic, structural and functional diversity was assessed in response to arsenic (As) pollution in a former gold mine soil. Ester-linked fatty acid methyl ester (EL-FAME), quantitative PCR (qPCR), denaturating gradient gel electrophoresis (DGGE), enzyme activities and MicroResp techniques were used.

Multivariate analysis showed that As bioavailability in soil was an important driver affecting microbial diversity. Microbial biomass assessed by EL-FAMEs and qPCR generally decreased under higher bioavailable As, as well as enzyme activities and C substrate utilization. Conversely, actinomycetes and fungal biomass increased along with total As content suggesting the selection of more resistant species.     

Isolation and Characterization of a Novel As(V)-Reducing Bacterium: Implications for Arsenic Mobilization and the Genus Desulfitobacterium

Dissimilatory arsenate-reducing bacteria have been implicated in the mobilization of arsenic from arsenic-enriched sediments. An As(V)-reducing bacterium, designated strain GBFH, was isolated from arsenic-contaminated sediments of Lake Coeur d'Alene, Idaho. Strain GBFH couples the oxidation of formate to the reduction of As(V) when formate is supplied as the sole carbon source and electron donor. Additionally, strain GBFH is capable of reducing As(V), Fe(III), Se(VI), Mn(IV) and a variety of oxidized sulfur species. 16S ribosomal DNA sequence comparisons reveal that strain GBFH is closely related to Desulfitobacterium hafniense DCB-2^T and Desulfitobacterium frappieri PCP-1^T. Comparative physiology demonstrates that D. hafniense and D. frappieri, known for reductively dechlorinating chlorophenols, are also capable of toxic metal or metalloid respiration. DNA-DNA hybridization and comparative physiological studies suggest that D. hafniense, D. frappieri, and strain GBFH should be united into one species. The isolation of an Fe(III)- and As(V)-reducing bacterium from Lake Coeur d'Alene suggests a mechanism for arsenic mobilization in these contaminated sediments while the discovery of metal or metalloid respiration in the genus Desulfitobacterium has implications for environments cocontaminated with arsenious and chlorophenolic compounds.     

Ultrastructure ofCatharanthus roseus cells culturedin vitro and exposed to conditions for alkaloid accumulation

Summary Periwinkle (Catharanthus roseus) cells cultured in 1-B 5 medium display the ultrastructure of parenchyma cells. The parenchyma character remained unchanged when cells were exposed to any one of three different conditions effecting alkaloid accumulation. Transfer of cells to alkaloid production medium for 2 weeks (condition 1) accorded two special features,i.e., unusually big lipid droplets in the cytoplasm and, upon fixation, one or several electron-dense droplets of spongy precipitate in vacuoles. Among hormone-autotrophic cultures (condition 2) some cells showed a fine electron-dense vacuolar precipitate. Addition ofPhythium homogenate (fungal elicitor) to cells cultured in 1-B 5-medium for 10 days (condition 3), cells showed a frequent appearance of singular big lipid droplets in the cytoplasm, whereas vacuoles remained devoid of precipitate. The appearance of big lipid droplets and of vacuolar precipitate is interpreted as progressing cytodifferentiation, but is coincidental with alkaloid accumulation.NRCC no. 24524.     

Transcriptional responses of Arabidopsis thaliana plants to As (V) stress

Background

Plants encode a large number of leucine-rich repeat receptor-like kinases. Legumes encode several LRR-RLK linked to the process of root nodule formation, the ligands of which are unknown. To identify ligands for these receptors, we used a combination of profile hidden Markov models and position-specific iterative BLAST, allowing us to detect new members of the CLV3/ESR (CLE) protein family from publicly available sequence databases.

Results

We identified 114 new members of the CLE protein family from various plant species, as well as five protein sequences containing multiple CLE domains. We were able to cluster the CLE domain proteins into 13 distinct groups based on their pairwise similarities in the primary CLE motif. In addition, we identified secondary motifs that coincide with our sequence clusters. The groupings based on the CLE motifs correlate with known biological functions of CLE signaling peptides and are analogous to groupings based on phylogenetic analysis and ectopic overexpression studies. We tested the biological function of two of the predicted CLE signaling peptides in the legume Medicago truncatula. These peptides inhibit the activity of the root apical and lateral root meristems in a manner consistent with our functional predictions based on other CLE signaling peptides clustering in the same groups.

Conclusion

Our analysis provides an identification and classification of a large number of novel potential CLE signaling peptides. The additional motifs we found could lead to future discovery of recognition sites for processing peptidases as well as predictions for receptor binding specificity.     

The removal of As(III) and As(V) from aqueous solutions by waste materials

The use of different waste materials such as Atlantic Cod fish scale, chicken fat, coconut fibre and charcoal in removing arsenic [As(III) and As(V)] from aqueous solutions was investigated. Initial experimental runs, conducted for both As(III) and As(V) with the aforementioned materials, demonstrated the potential of using Atlantic Cod fish scale in removing both species of arsenic from aqueous streams. Therefore, the biosorbent fish scale was selected for further investigations and various parameters such as residence time, adsorbent dose, initial concentration of adsorbate, grain size of the adsorbent and pH of the bulk phase were studied to establish optimum conditions. The maximum adsorption capacity was observed at pH value 4.0. The equilibrium adsorption data were interpreted by using both Freundlich and Langmuir models. Rapid small-scale column tests (RSSCT) were also performed to determine the breakthrough characteristics of the arsenic species with respect to packed biosorbent columns.     

Identification of Agrostis tenuis leaf proteins in response to As(V) and As(III) induced stress using a proteomics approach

Agrostis tenuis is known to be able to metabolise arsenate (As(V)) and arsenite (As(III)) which are toxic salts for most plants. A proteomic approach was developed to identify proteins expressed in response to treatments with these salts. A. tenuis plants were grown hydroponically in the presence of 134 and 668 μM As(V) or As(III) for 8 days at pH 7. During arsenic treatments, leaves showed chlorotic symptoms but fresh and dry leaf weights were not reduced, except in the presence of 668 μM As(III). On the contrary, a slight increase in biomass was observed with high As(V) concentrations. Thus, A. tenuis was more sensitive to As(III) than to As(V) and biomass was affected. Proteomic analysis enabled identification of a set of A. tenuis leaf proteins differentially expressed in response to arsenic exposure including a major functionally homogeneous group of enzymes such as oxygen-evolving enhancer protein, RuBisCO small and large subunits, RuBisCO activase and ATP synthase involved in the Calvin or Krebs cycle. The adaptative response to treatments resulted in partial disruption of the photosynthetic processes with prominent fragmentation of the RubisCO. Other proteins expressed differently from controls were identified and are possibly involved in the tolerance mechanisms of A. tenuis to arsenic treatments.     

Factors Controlling the Bioaccessibility of Arsenic(V) and Lead(II) in Soil

The relative oral bioaccessibility of labile Pb(II) and As(V) added to soils was investigated in a well-characterized soil using a physiologically based extraction test (PBET) to simulate metal solubility in a child's digestive system. The effect of soil and PBET (i.e., simulated stomach and small intestine) pH, soil metal concentration, soil to solution ratio, and soil-metal aging time were investigated. Arsenic bioaccessibility was relatively unaffected by a variation in simulated stomach and small intestine pH over the range 2 to 7 and soil pH over the range 4.5 to 9.4. In contrast, Pb(II) bioaccessibility was strongly dependent on both the simulated stomach, small intestine, and soil pH, showing enhanced sequestration and decreased bioaccessibility at higher pH values in all cases. Although the bioaccessibility of Pb(II) was constant over the concentration range of approximately 10 to 10,000?mg/kg, the As(V) bioaccessibility significantly increased over this concentration range. The bioaccessibility of both arsenic and lead increased as the soil-to-solution ratio decreased from 1:40 to 1:100. Additional lead sequestration was not observed during 6 months of soil aging, but As(V) bioaccessibility decreased significantly during this period.     

Metal accumulation and damage in rice (cv. Vialone nano) seedlings exposed to cadmium

The effect of exposure to increasing cadmium concentrations was analyzed in rice seedlings (cv. Vialone nano). The highest Cd accumulation was found in roots, mostly in the apoplastic environment. Cd taken up in cells led to an increase in sulfhydryl groups, the appearance of phytochelatins, and formation of electron-dense vacuolar inclusions. The metal-exposure inhibited root growth and also interfered with correct root morphogenesis, causing disordered division and abnormal and forward enlargement of epidermal and cortical cell layers in the apical region. Cd accumulation in shoots was lower than in roots. In leaf cells, there was neither a substantial increase in sulfhydryl groups nor the appearance of phytochelatins. Shoot growth was reduced and, differently from in roots, leaf cell enlargement was inhibited. Chloroplasts had lowered contents of chlorophyll and a reduced number of thylakoids, but underwent structural alterations only at the highest Cd concentration tested (250 μM). Photosynthetic activity was limited due to the curtailment of CO₂ availability caused by the greater resistance of Cd-exposed leaves. The damage suffered by seedlings worsened with the increase in Cd concentration, but was already evident at the lowest concentration examined (50 μM), showing that the cv. Vialone nano has a Cd-sensitivity higher than other rice cultivars.     

Arsenic(V) biosorption by charred orange peel in aqueous environments

Biosorption efficiency of natural orange peel (NOP) and charred orange peel (COP) was examined for the immobilization of arsenate (As(V)) in aqueous environments using batch sorption experiments. Sorption experiments were carried out as a function of pH, time, initial As(V) concentration and biosorbent dose, using NOP and COP (pretreated with sulfuric acid). Arsenate sorption was found to be maximum at pH 6.5, with higher As(V) removal percentage (98%) by COP than NOP (68%) at 4 g L^?1 optimum biosorbent dose. Sorption isotherm data exhibited a higher As(V) sorption (60.9 mg g^?1) for COP than NOP (32.7 mg g^?1). Langmuir model provided the best fit to describe As(V) sorption. Fourier transform infrared spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy analyses revealed that the –OH, –COOH, and –N-H surface functional groups were involved in As(V) biosorption and the meso- to micro-porous structure of COP sequestered significantly (2-times) higher As(V) than NOP, respectively. Arsenate desorption from COP was found to be lower (10%) than NOP (26%) up to the third regeneration cycle. The results highlight that this method has a great potential to produce unique ‘charred’ materials from the widely available biowastes, with enhanced As(V) sorption properties.     

Reduction kinetics of As (V) to As (III) by a dissimilatory arsenate-reducing bacterium, Bacillus sp. SF-1

This study proposes a kinetic model that accounts for the toxicity of both arsenate and arsenite and characterizes the arsenate reduction ability of a dissimilatory arsenate-reducing bacterium, Bacillus sp. SF-1 as a bioremediation agent. The model results correlated well with a series of batch reduction experiments conducted anaerobically in serum bottles with initial arsenate concentrations of 360, 735, and 1,500 mg-As/L. The reduction rate was expressed by the Haldane equation that describes the inhibitory effect of high concentrations of arsenate. The reduction rate constant k(r), half saturation constant K(S), and inhibition constant K(I) were estimated respectively as 1.2 x 10(9) mg-As/cells/h, 1.5 x 10(2) mg-As/L, and 4.2 x 10(2) mg-As/L. Lethal effects of arsenite that is accumulated as the end-product of arsenate reduction were expressed by the first-order term with a lethal constant of 2.7 x 10(-4) L/mg-As/h. The yield for the bacterial cells by arsenate respiration was estimated at 4.0 x 10(8) cells/mg-As.     

Toxicity and bioremediation of As(III) and As(V) in the green microalgae Botryococcus braunii: A laboratory study

Worldwide threats of fuel shortages in the near future and climate change because of greenhouse gas emissions are posing severe challenges and therefore it is vital to search for sustainable ways of preventing the consequences. The dual use of microalgae for phycoremediation and biomass production for sustainable biofuel production is a viable choice. Phycoremediation of As(III) and As(V) ions using microalgae was investigated in a two-staged batch reactor. Accumulation and toxicity of inorganic arsenic forms (As(III) and As(V)) to green microalgae Botryococcus braunii depend on environmental factors. Dissolved oxygen and pH cycles did not significantly differ due to the absence or presence of arsenic (either As(III) or As(V)) ions in the culture. Monod model was utilized for representing the growth kinetics of microalgae in pure media containing various concentrations of nitrate ions. Maximum specific growth rate and saturation constant were found to be 0.14788 d^?1 and 0.00105 g/L, respectively. With the increase in concentration of phosphate in growth medium, the growth of microalgae increased. Media with NaCl (1.0 g/L) and NaHCO₃ (1 g/L) resulted in higher maximum biomass concentration. Effect of coexisting ions on phycoremediation of As(III) and As(V) ions using microalgae was studied.     

Antioxidant enzymes and thiol/disulfide status in the digestive gland of the brown mussel Perna perna exposed to lead and paraquat

Lead (Pb) and paraquat (PQ) have different toxic mechanisms associated with cell damage. Pb may induce alterations in zinc containing proteins, including the known inhibitory effect on the enzyme delta-aminolevulinic acid dehydratase, disrupting the heme-synthesis pathway. During PQ biotransformation, redox cycle reactions enhance oxyradical production, which may lead to pro-oxidative conditions. In this study, we analyzed the effects of Pb and PQ on antioxidant enzymes and thiol status, using the digestive glands of the mussel Perna perna collected in a mussel farm on Santa Catarina Island. Mussels were exposed to Pb (1 ppm) and PQ (10 ppm), either separately or concomitantly, for 48 h. We were unable to detect an effect of Pb treatment on the enzymes, catalase, glucose 6-phosphate dehydrogenase (G6PDH), glutathione S-transferase (GST) and glutathione reductase (GSSG-reductase), which contrasts to the effect of PQ, increasing GSSG-reductase and G6PDH, but decreasing GST activity. The thiol status showed a pro-oxidative trend, observed mainly through a decrease in the reduced/oxidized glutathione ratio, despite the total-glutathione increase. Protein-mixed disulfides and protein thiols did not change by the treatments. The observed effects of PQ and Pb were consistent with literature. Pb had a suppressive effect on the enzymatic changes elicited by PQ, while the changes in the thiol/disulfide parameters were retained.     

Tissue-specific accumulation and speciation of selenium in rainbow trout (Oncorhynchus mykiss) exposed to elevated dietary selenomethionine

The toxicity of selenium in fish is influenced by its chemical speciation and the exposure route. In the natural environment, selenium exposure to fish occurs primarily in the form of selenomethionine in diet. Thus, the main objective of this study was to examine the tissue-specific selenium burden and speciation in fish exposed to elevated dietary selenomethionine. Rainbow trout (Oncorhynchus mykiss) were treated with dietary selenomethionine (40 μg g(-1) dry mass) for 2 weeks, and at the end of the exposure different tissue samples were collected to assess the tissue-specific distribution and speciation of selenium. We used synchrotron-based X-ray absorption near edge spectroscopy (XANES) to determine the selenium speciation profile. Selenomethionine, selenocysteine and selenocystine were found to be the predominant form of selenium in all of the tissues; however their relative proportion varied across different tissues. In general, the organs primarily involved in selenium handling in fish (e.g., liver, kidney) accumulated a higher percentage of selenocystine. We also found that dietary selenomethionine exposure resulted into a marked increase in selenium burden of all major tissues in fish including the brain. Collectively, our findings provide new insights into the tissue-specific distribution and speciation of selenium in fish exposed to selenomethionine via diet.