No description available.

The overall goal of the present research project was to investigate the physiology of dietary iron absorption and its interactions with the uptake and metabolism of other divalent metals, especially cadmium, in freshwater fish, using rainbow trout (Oncorhynchus mykiss) as a model species. Using intestinal sac preparations, iron absorption was found to occur along the entire intestinal tract of fish, with anterior intestine being the major site of absorption compared to either mid or posterior intestine. Ferrous iron was more bioavailable than ferric iron, and the uptake of ferrous iron was significantly reduced at alkaline pH (p < 0.05). These findings suggested that a homolog of the mammalian apical ferrous iron transporter, divalent metal transporter-1 (DMT1, a Fe2+/H+ symporter), is involved in the absorption of iron in the fish intestine. Ferric iron appeared to be absorbed through the same pathway as ferrous iron following reduction by an apical ferric reductase. Several divalent metals, both essential (nickel, copper and zinc) and non-essential (cadmium and lead), inhibited intestinal ferrous iron absorption in fish. Importantly, elevated luminal iron reciprocally reduced the accumulation of cadmium in the fish intestine, indicating the significance of the iron transport pathway in dietary cadmium absorption. Two different DMT1 isoforms, Nramp-â and -ã, were found to be expressed along the entire gastrointestinal tract of fish. My study showed that in isolated rainbow trout enterocytes, ferrous iron uptake occurred through a saturable and proton-dependent process, providing further evidence of DMT1-mediated ferrous iron transport. Both cadmium and lead inhibited ferrous iron uptake in the enterocytes in a concentration-dependent manner. Kinetic characterization revealed that the apparent affinity for ferrous iron uptake is significantly decreased (increased Km) in the presence of either cadmium or lead (p < 0.05), whereas the maximum uptake rate (Jmax) remains unchanged. These results indicated that the interaction between ferrous iron and cadmium or lead is competitive in nature, and the uptake of these metals occurs through a common transport pathway (likely DMT1). The uptake characteristics of cadmium were further examined in isolated rainbow trout enterocytes, and my findings indicated that in addition to DMT1, cadmium uptake can be mediated by zinc transport pathway (ZIP8, a Zn2+/HCO3- symporter). My study also showed that cysteine-conjugated cadmium was readily bioavailable to fish enterocytes, possibly via a cysteine-specific transport pathway. The efflux of cadmium from the enterocytes was found to occur via an ATPase-driven pathway. On the other hand, chronic exposure to dietary cadmium at an environmentally-relevant concentration significantly increased cadmium burden in target organs as well as in the whole-body of fish (p < 0.05). Exposure to dietary cadmium increased the mRNA expression level of key stress-inducible proteins such as metallothioneins (MT-A and MT-B) and heat shock proteins-70 (HSP-70a and HSP-70b). Interestingly, each MT and HSP-70 mRNA isoform responded differently in various target organs of fish following dietary cadmium exposure. Fish exposed to dietary cadmium also exhibited an increase in the hepatic transferrin mRNA level as well as the plasma transferrin protein level, indicating the role of transferrin in cadmium handling in fish. Importantly, an iron-supplemented diet reduced cadmium burden in the gut and the whole-body, and ameliorated the expression of MT and HSP-70 genes in fish. These results suggested the protective effects of elevated dietary iron against chronic dietary cadmium toxicity in fish. Overall, findings from the present research project provided novel and important physiological and molecular insights into the uptake, interactions and homeostasis of dietary divalent metals in freshwater fish. This information greatly enhances our current understanding of the toxicological implications for dietary metal exposure in metal contaminated wild fish populations, and may ultimately help the regulators to develop better strategies for ecological risk assessment of metals.

The overall goal of the present research project was to investigate the physiology of dietary iron absorption and its interactions with the uptake and metabolism of other divalent metals, especially cadmium, in freshwater fish, using rainbow trout (Oncorhynchus mykiss) as a model species. Using intestinal sac preparations, iron absorption was found to occur along the entire intestinal tract of fish, with anterior intestine being the major site of absorption compared to either mid or posterior intestine. Ferrous iron was more bioavailable than ferric iron, and the uptake of ferrous iron was significantly reduced at alkaline pH (p < 0.05). These findings suggested that a homolog of the mammalian apical ferrous iron transporter, divalent metal transporter-1 (DMT1, a Fe2+/H+ symporter), is involved in the absorption of iron in the fish intestine. Ferric iron appeared to be absorbed through the same pathway as ferrous iron following reduction by an apical ferric reductase. Several divalent metals, both essential (nickel, copper and zinc) and non-essential (cadmium and lead), inhibited intestinal ferrous iron absorption in fish. Importantly, elevated luminal iron reciprocally reduced the accumulation of cadmium in the fish intestine, indicating the significance of the iron transport pathway in dietary cadmium absorption. Two different DMT1 isoforms, Nramp-â and -ã, were found to be expressed along the entire gastrointestinal tract of fish. My study showed that in isolated rainbow trout enterocytes, ferrous iron uptake occurred through a saturable and proton-dependent process, providing further evidence of DMT1-mediated ferrous iron transport. Both cadmium and lead inhibited ferrous iron uptake in the enterocytes in a concentration-dependent manner. Kinetic characterization revealed that the apparent affinity for ferrous iron uptake is significantly decreased (increased Km) in the presence of either cadmium or lead (p < 0.05), whereas the maximum uptake rate (Jmax) remains unchanged. These results indicated that the interaction between ferrous iron and cadmium or lead is competitive in nature, and the uptake of these metals occurs through a common transport pathway (likely DMT1). The uptake characteristics of cadmium were further examined in isolated rainbow trout enterocytes, and my findings indicated that in addition to DMT1, cadmium uptake can be mediated by zinc transport pathway (ZIP8, a Zn2+/HCO3- symporter). My study also showed that cysteine-conjugated cadmium was readily bioavailable to fish enterocytes, possibly via a cysteine-specific transport pathway. The efflux of cadmium from the enterocytes was found to occur via an ATPase-driven pathway. On the other hand, chronic exposure to dietary cadmium at an environmentally-relevant concentration significantly increased cadmium burden in target organs as well as in the whole-body of fish (p < 0.05). Exposure to dietary cadmium increased the mRNA expression level of key stress-inducible proteins such as metallothioneins (MT-A and MT-B) and heat shock proteins-70 (HSP-70a and HSP-70b). Interestingly, each MT and HSP-70 mRNA isoform responded differently in various target organs of fish following dietary cadmium exposure. Fish exposed to dietary cadmium also exhibited an increase in the hepatic transferrin mRNA level as well as the plasma transferrin protein level, indicating the role of transferrin in cadmium handling in fish. Importantly, an iron-supplemented diet reduced cadmium burden in the gut and the whole-body, and ameliorated the expression of MT and HSP-70 genes in fish. These results suggested the protective effects of elevated dietary iron against chronic dietary cadmium toxicity in fish. Overall, findings from the present research project provided novel and important physiological and molecular insights into the uptake, interactions and homeostasis of dietary divalent metals in freshwater fish. This information greatly enhances our current understanding of the toxicological implications for dietary metal exposure in metal contaminated wild fish populations, and may ultimately help the regulators to develop better strategies for ecological risk assessment of metals.

No description available.

No description available.

Very little information exists on the marine biogeochemistry of Rh, Pd and Pt, or the platinum group elements (PGE), an emerging group of contaminants whose principal emissions are associated with the abrasion of the catalytic converter in motor vehicles and chemotherapy drugs discharged in hospital wastes. In this study, Rh(III), Pd(II) and Pt(IV) were added individually and in combination to cultures of the marine microalga, Chlorella stigmatophora, maintained in coastal seawater at 15oC and under fluorescence lighting both in the presence and absence of trace nutrients (e.g. Fe, Co, Zn and EDTA). The accumulation of PGE was established under varying conditions (pH, algal biomass, PGE concentration, time) by ICP-MS analysis of seawater and nitric acid digests and EDTA washes of the alga, the latter giving a measure of PGE adsorption by C. stigmatophora. Under all conditions the extent of accumulation was in the order: Rh &gt; Pd &gt;&gt; Pt. In short-term (24-h) exposures, accumulation isotherms were quasi-linear up to PGE concentrations of 30 ug L-1, although Pd displayed convexity, hence saturation of available binding sites, at greater concentrations. The pH, adjusted between about 5.5 and 9.5 by addition of acid or base, did not have a great impact on PGE accumulation, with Rh displaying a moderate increase in accumulation and Pd a moderate reduction with increasing pH. More important, all PGE displayed a significant reduction in accumulation on a weight-normalized basis with increasing concentration of algae, an effect not reported for metal-marine algal interactions previously in the literature. Longer-term experiments showed that the rates of both overall accumulation and internalization were greatest for Pd and least for Pt. Consistent with this observation, the toxicity to C. stigmatophora evaluated by both pigment content and growth rate, was significantly greater for Pd than for Pt. Differences in the biogeochemical behaviours among the PGE are attributed to differences in their aqueous speciation in seawater, different affinities for the algal surface, different tendencies to cross the cell membrane, and especially with regard to Pd and Pt, differences in the rates of these interactions. Thus, although the equilibrium chemistries of Pd and Pt are very similar, their differential biogeochemistries are the result of kinetic constraints on reactions involving the latter. Because the environmental concentrations of PGE are predicted to increase with increasing emissions from vehicles and hospitals, the results of this study make an important contribution to an improved understanding of the likely effects and fates of these emerging contaminants in the marine environment. The results are also more generally important to an improved understanding of the interactions of trace metals with microalgae in seawater.

Heavy metals are one of the most important environmental pollutants. In recent years, many low cost stretages of bioremediation for contaminated sites by heavy metals, such as fungi, bacteria and plants have been investigated for their biosorption capacity towards heavy metals. The uses of plant species for remediate contaminated sites by heavy metals are so called phytoremediation. The purpose of the first parts of this study are to (1) evaluate bioavailability of Cadmium (Cd) in contaminated soil and phytoremediation potential by three plant species, Vetiveria zizanioides, Pteris multifida, and Alternanthera philoxeroides (Mart.), and (2) realized the influence of photosynthetic bacteria (PSB) on the uptake of Cd in the three species. The results showed that the Alternanthera philoxeroides (Mart.) could accumulate the highest concentration of Cd among the three species, in which the Cd concentration of plant tissue increased with the concentration in soil. The highest concentration of Cd (164.9 mg kg-1) was found in the below-ground parts of Alternanthera philoxeroides (Mart.) at the 8th week of culturing period. However, the species of Vetiveria zizanioides could accumulate the largest total Cd, up to 547.5 £gg/ plant, which thus extracted the greatest amounts of Cd from the soil. Therefore, in the first part of this study the species of Vetiveria zizanioides was concluded to be the best accumulator among the three plant species. In addition, the concentration of Cd in the species of Pteris multifida was found significantly increased after PSB was added into the soil, but the plants died later due to Cd stress. The experimental results also showed that PSB seemed to be not suitable for each species used in this study to accumulate Cd from Cd-contaminated soil. In the second part of this research, both pot and field experiments were conducted to (1) evaluate bioavailability of copper (Cu), lead (Pb) and zinc (Zn) in contaminated soil and phytoremediation potential by domesticated plants, Bidens pilosa and Passiflora foetida inoculated with arbuscular mycorrhizal (AM) fungi, and to (2) compare the results of pot and field experiments. The plant species of Bidens pilosa inoculated with AM fungi had significantly higher Cu concentrations in the shoots and roots than non-inoculated plants. The plant species of Passiflora foetida inoculated with AM fungi also had significantly higher Cu and Pb concentrations in the roots than non-inoculated plants. When we found that the root dry weight of Passiflora foetida inoculated with AM fungi dramatically increased, the concentrations of Cu, Pb and Zn in the root of the plant species increased by 9-14 times, comparing with the plants without inoculation of AM fungi. The AM fungi have potential either to promot plant growth or to increase heavy metal accumulation. The values of element translocation proportion from root to shoot was Zn>Cu>Pb for the plant species in both pot and field experiments. For both experiments, the results of pot test and field test were significantly different. The concentrations of pot tests were found higher than the field tests, and some values of pot tests were even found significantly greater than those in the field tests. In the third part of this study, the field experiments were conducted to test the feasibility of using domesticated vegetations for phytoremediation of the contaminated farmland. The objectives of this study were (1) to acquire information about the ability of five plant species growing wild in the polluted area to accumulate Cu, Pb and Zn, (2) to investigate the season effects on phytoremediaton of five plant species and evaluate the total uptake of heavy metal, and (3) to run both pot tests and a field trial of phytotremediation to compare their differences. The experimental results showed that three maximum toxic elements in a pot were 3020 mg kg-1 Pb, 232 mg kg-1 Cu and 1012 mg kg-1 Zn respectively. The Cu concentrations of the five plant species collected from the polluted plots ranged from 0.7 to 17.43 mg kg-1. The range of variation of Pb in plant tissues was measured varied from 2.29 to 81.65 mg kg−1, while a wide range of Zn concentrations was found from 12.84 to 192.85 mg kg-1 among the plants collected at the contaminated plots. In comparison to winter season, the Zn concentrations in Broussonetia papyrifera, Passiflora foetida and Saccharum sinensis collected in summer season was significantly higher. The higher Cu concentrations were obtained in both plant species of Bidens pilosa and Mimosa diplotricha in summer season. However, Pb concentrations in Saccharum sinensis collected in winter were significantly higher than those in the same plant species collected in summer. Bidens pilosa was also found having the highest total amount of Cu and Zn. The highest total amount of Pb was found in Mimosa diplotricha. For both plant species, both of the pot and field tests were different.

Manganese and iron homeostasis play an important role in oxidative stress protection in a variety of organisms. However, the transport and role of these metals in the periodontal pathogen Porphyromonas gingivalis were not well understood. Analysis of the genome of P. gingivalis W83 revealed the presence of two genes encoding homologs of ferrous iron transport protein, FeoB1 and FeoB2. The goal of this study was to determine the role of these two putative transporters in metal transport, their contributions to resistance to oxygen radicals and intracellular survival as well as the regulation and genetic organization of these two loci. Isogenic mutant strains deficient in FeoB1 and FeoB2, respectively, were generated and used in this study. The transport ability for manganese and iron was assessed and compared in feoB1, feoB2 mutant and wild type strains using 55Fe2+ and 54Mn2+. We demonstrated that feoB2 encodes a major manganese transporter, while FeoB1 functions as a major ferrous iron transporter. The roles of P. gingivalis FeoB1 and FeoB2 in oxidative stress defense and intracellular survival in host cells were determined using an oxidative stress survival assay and an in vitro infection assay, respectively. The feoB2 mutant exhibited reduced survival after exposure to H2O2 and to atmospheric oxygen and inside the host cells compared to the wild-type strain and its revertant, while the feoB1 mutant survived as well as the wild type strain under oxidative stress and possessed better capability to adhere to and survive in the host cells. Our results demonstrate that FeoB2 is required for protection of the bacterium from oxidative stress and for intracellular survival of P. gingivalis in host cells. However, FeoB1 is dispensable for both processes. Quantitative RT-PCR analysis revealed that expression of feoB2 in P. gingivalis is induced by oxidative stress. However, expression of feoB1 increased 2-fold upon exposure to lower growth temperature. Both observed inductions were specific and not detected under other stress conditions. We have also showed in this study that feoB2 is the second gene transcribed in an operon that is composed of a total of five genes and feoB1 is only co-transcribed with one downstream gene encoding a hypothetical protein. Notably, we also identified tandem repeats with potential to form stable stem-loop RNA secondary structure within the feoB2 and feoB1 transcripts.To our knowledge, this study has demonstrated the first connection among metal homeostasis, oxidative stress resistance and response to host cells in the periodontal pathogen, P. gingivalis.

No description available.

No description available.