Inorganic Iron Research Articles

Influence of ocean acidification on the complexation of iron and copper by organic ligands in estuarine waters

The uptake of anthropogenic atmospheric CO2 by the oceans causes a shift in the carbonate chemistry system which includes a lowering of pH; this process has been termed ocean acidification. Our understanding of the specific effects of ocean acidification on chemical speciation of trace metals, in particular on organic–metal interactions, is limited. In this study we have experimentally determined the effects of changing pH from 8.3 to 6.8 (on the NBS scale) on the speciation of iron and copper in estuarine waters. Our experimental results indicated that complexation of iron and copper would decrease and inorganic iron and copper concentrations increase, as pH decreased, although it was not possible to confidently quantify changes in speciation at lower pH due to constraints of the analytical technique. In addition to our experimental approach, we used a non-ideal competitive adsorption (NICA)–Donnan model to determine the chemical speciation of iron and copper as a function of pH. The NICA–Donnan model was optimised in order to produce similar metal binding characteristics to those observed in our sample across the pH range examined in our study. The model allowed for simultaneous modelling of solubility and organic complexation. Model results indicated that a decrease in iron and copper binding by organic matter at lower pH, coupled with increased solubility (for iron), resulted in a 3 fold increase in inorganic iron concentration and a 6 fold increase in inorganic copper concentration at pH of 7.41 compared to a pH of 8.18 (expressed on the total scale). This compared to a 10 fold increase in inorganic iron concentration, and a 5 fold increase in inorganic copper concentration, obtained at pH8.18, when the dissolved organic carbon (DOC) concentration was halved. Variability in DOC might thus be expected to have a greater impact on metal speciation in seawater, than projected variability in pH resulting from increases in atmospheric CO2. Our study therefore suggests that increases in the concentrations of the more bioavailable inorganic iron and copper species in estuarine waters resulting from increased pCO2 are likely to occur, but that such changes will be moderate in magnitude.

A Comparative Study of Iron Uptake Rates and Mechanisms amongst Marine and Fresh Water Cyanobacteria: Prevalence of Reductive Iron Uptake.

In this contribution, we address the question of iron bioavailability to cyanobacteria by measuring Fe uptake rates and probing for a reductive uptake pathway in diverse cyanobacterial species. We examined three Fe-substrates: dissolved inorganic iron (Fe') and the Fe-siderophores Ferrioxamine B (FOB) and FeAerobactin (FeAB). In order to compare across substrates and strains, we extracted uptake rate constants (kin = uptake rate/[Fe-substrate]). Fe' was the most bioavailable Fe form to cyanobacteria, with kin values higher than those of other substrates. When accounting for surface area (SA), all strains acquired Fe' at similar rates, as their kin/SA were similar. We also observed homogeneity in the uptake of FOB among strains, but with 10,000 times lower kin/SA values than Fe'. Uniformity in kin/SA suggests similarity in the mechanism of uptake and indeed, all strains were found to employ a reductive step in the uptake of Fe' and FOB. In contrast, different uptake pathways were found for FeAB along with variations in kin/SA. Our data supports the existence of a common reductive Fe uptake pathway amongst cyanobacteria, functioning alone or in addition to siderophore-mediated uptake. Cyanobacteria combining both uptake strategies benefit from increased flexibility in accessing different Fe-substrates.

Screening of iron-enriched fungus from natural environment and evaluation of organically bound iron bioavailability in rats

Iron is an essential element for nearly all living organisms, and its deficiency is the most common form of malnutrition in the world. The organic forms of trace elements are considered more bioavailable than the inorganic forms. Although Saccharomyces cerevisiae can enrich metal elements and convert inorganic iron to organic species, its tolerability and transforming capacity are limited. The aim of this study was to screen higher biomass and other iron-enriched fungi strains besides Saccharomyces cerevisiae from the natural environment. A PDA medium containing 800 μg/mL iron was used for initial screening. Fifty strains that tolerated high iron concentration were isolated from the natural environment, and only one strain, No.BY1109, grew well at Fe (II) concentration of 10,000μg/ml. According to morphological characterization, 18S rDNA sequence analysis, and biophysical and biochemical characterization, the strain No.BY1109 was identified as Rhodotorula. The iron content of No.BY1109 (10 mg Fe/g dry cell) was determined using atomic absorption spectrometry. The results of distribution of iron in the cells showed that iron ion was mainly chelated in the cell walls and vacuoles. The bioavailability in rats confirmed that strain No.BY1109 had higher absorption efficiency than that of ferrous sulfate after single dose oral administration. The present study introduces new iron supplements, and it is a basis for finding new iron supplements from natural environment.

Assessing the utility of trace and rare earth elements as biosignatures in microbial iron oxyhydroxides

Microbial iron oxyhydroxides are common deposits in natural waters, recent sediments and mine drainage systems and often contain significant accumulations of trace and rare earth elements (TREE). TREE patterns are widely used to characterize minerals and rocks, and to elucidate their evolution and origin. Whether and which characteristic TREE signatures distinguish between a biological and an abiological origin of iron minerals is still not well understood. Long-term flow reactor studies were performed in the Aspo Hard Rock Laboratory to investigate the development of microbial mats dominated by iron-oxidizing bacteria, namely Mariprofundus sp. and Gallionella sp. The experiments investigated the accumulation and fractionation of TREE under controlled conditions and enabled us to assess potential biosignatures evolving within the microbial iron oxyhydroxides. Concentrations of Be, Y, Zn, Zr, Hf, W, Th, Pb, and U in the microbial mats were 1e3- to 1e5-fold higher than in the feeder fluids whereas the rare earth elements and Y (REE+Y) contents were 1e4 and 1e6 fold enriched. Except for a hydrothermally induced Eu anomaly, the normalized REE+Y patterns of the microbial iron oxyhydroxides were very similar to published REE+Y distributions of Archaean Banded Iron Formations. The microbial iron oxyhydroxides from the flow reactors were compared to iron oxyhydroxides that were artificially precipitated from the same feeder fluid. These abiotic and inorganic iron oxyhydroxides show the same REE+Y distribution patterns. Our results indicate that the REE+Y mirror quite exactly the water chemistry, but they do not allow to distinguish microbially mediated from inorganic iron precipitates. All TREE studied showed an overall similar fractionation behavior in biogenic, abiotic and inorganic iron oxyhydroxides. Exceptions are Ni and Tl, which were only accumulated in the microbial iron oxyhydroxides and may point to a potential usage of these elements as microbial biosignatures.

The role of fossil fuel combustion on the stability of dissolved iron in rainwater

The concentration of dissolved Fe(II) has decreased in coastal NC rainwater because of less complexation and stabilization of Fe(II) (aq) by automobile and coal combustion emissions. Better emission control has removed stabilizing organic ligands hence dissolved Fe(II) currently occurs more as inorganic iron, which is not protected against oxidation. Increasing rainwater pH allows oxidation by molecular O2 in addition to H2O2 and also increases the ratio of the ion pair Fe(OH)+ to Fe(II) free ion, which increases the oxidation rates by both H2O2 and molecular oxygen. The concentration of H2O2 in rain has increased; hydrogen peroxide is the primary oxidant of inorganic Fe(II) in precipitation. The East Coast of the USA is also receiving less rain of terrestrial origin, which tends to be higher in dissolved iron and organic compounds. All these factors operate in the same direction and contribute to the lower concentrations and lack of stability of Fe(II) in rainwater currently observed. Results of this study suggest that wet deposition of soluble Fe(II) is an episodic, temporally variable factor in the iron cycle in oceanic regions adjacent to developed or developing coastal regions.

Efeito do ácido fítico e do ferro inorgânico dietéticos na qualidade da carne suina refrigerada

O estudo foi conduzido com o objetivo de avaliar o efeito da suplementação do ferro inorgânico e do ácido fítico na dieta de suínos em terminação sobre a qualidade da carne após 24 horas e 7 dias de refrigeração. Foram utilizados 40 suínos machos castrados, na fase de terminação, de genética comercial, com 64,34 ± 6,64 kg de peso médio inicial e 108 dias de idade. Os animais foram pesados e alojados individualmente em baias de alvenaria com área de 3 m2 e piso compacto, onde receberam água e ração à vontade durante o período de 30 dias. O delineamento experimental foi em blocos casualizados, em modelo fatorial 2 x 2, sendo os fatores correspondentes às dietas com e sem ferro inorgânico suplementar (FeI) e com dois níveis de ácido fítico (AF) na ração, alto (4,85%) e baixo (2,98%). Ao atingirem 100,76 ± 6,54 kg de peso médio, os animais foram abatidos, sendo coletadas amostras do músculo longissimus dorsi para análise da qualidade da carne. As amostras foram submetidas às avaliações de pH, cor, marmorização, perda de água por pressão, força de cisalhamento, composição de ferro e oxidação lipídica. Os valores das variáveis avaliadas não foram diferentes entre os fatores, excetuando-se a concentração de ferro no músculo, que foi superior para a dieta com a inclusão de ferro inorgânico. A oxidação lipídica não foi influenciada pela presença ou não do AF e FeI. Os resultados demonstraram que dietas com níveis de AF mais elevados, com ou sem a suplementação de FeI, podem ser utilizadas para suínos em fase de terminação sem prejuízos à qualidade da carne durante a fase de refrigeração

Mineral deficiency predisposes occurrence of retention of placenta in crossbred

Aim: The present study was carried out to investigate the relationship between blood serum concentrations of macro and micro minerals and development of retention of placenta (ROP) in crossbred cattle. Materials and Methods: The present study was carried out at Instructional Livestock Farm, Bihar Veterinary College and local Khatals in and around Patna. A total of 20 crossbred cattle (n=10 with normal expulsion of the placenta as control and n=10 with ROP) were selected in the present study. Blood samples were collected from these animals and serum was separated and stored in the deep freezer at −20°C till further analysis. The estimation of serum macro-minerals (Ca, P, Ca/P ratio) was done by Span diagnostic Kits (Surat, India) and trace minerals or micro-minerals (Zn, Cu, and Fe) were analyzed by atomic absorption spectrophotometer (Perkin Elmer AAS 220). Mean values were compared between both the groups at 0 h (at parturition) and 12 h after parturition. Results: The mean values of serum calcium and zinc were found significantly lower in cattle having ROP than control at both 0 h and 12 h after parturition. The mean values of serum Ca and P ratio obtained at 0 hour were significantly lower in ROP groups as compared to control groups and non-significant at 12 h. The mean values of serum inorganic phosphorus, copper and iron was found non-significantly lower in ROP cases as compared to control. Conclusions: Macro and micro mineral deficiency such as calcium, iron, zinc and copper in blood serum may be predisposing factor for the occurrence of retention of placenta in crossbred cattle.

Studies on different iron source absorption by in situ ligated intestinal loops of broilers.

The objective of this study was to investigate the iron source absorption in the small intestine of broiler. In situ ligated intestinal loops of 70 birds were poured into one of seven solutions, including inorganic iron (FeSO4, Fe2(SO4)3), organic Fe glycine chelate (Fe-Gly(II), Fe-Gly(III)), the mixtures (FeSO4 with glycine (Fe+Gly(II)), Fe2(SO4)3 with glycine (Fe+Gly(III)), and no Fe source (control). The total volume of 3-mL solution (containing 1mg of elemental Fe) was injected into intestinal loops, and then 120-min incubation was performed. Compared with inorganic iron groups, in which higher FeSO4 absorption than Fe2(SO4)3 was observed, supplementation with organic Fe glycine chelate significantly increased the Fe concentration in the duodenum and jejunum (P < 0.05), however, decreased DMT1 and DcytB messenger RNA (mRNA) levels (P < 0.05). Organic Fe glycine chelate (Fe-Gly(II), Fe-Gly(III)) increased serum iron concentration (SI), compared with inorganic 3 valence iron groups (Fe2(SO4)3 and Fe+Gly(III)) (P < 0.05); moreover, lower TIBC value was observed for the chelate (P < 0.05); however, mixture of inorganic iron and glycine did not have a positive role at DMT1 and DcytB mRNA levels, SI and Fe concentrations in the small intestine. Those results indicated that the absorption of organic Fe glycine chelate was more effective than that of inorganic Fe, and the orders of iron absorption in the small intestine were: Fe-Gly(II), Fe-Gly(III) > FeSO4, Fe+Gly(II) > Fe2(SO4)3, Fe+Gly(III). Additionally, the simple mixture of inorganic iron and glycine could not increase Fe absorption, and the duodenum was the main site of Fe absorption in the intestines of broilers and the ileum absorbed iron rarely.

A pulsed light system for the disinfection of flow through water in the presence of inorganic contaminants.

The use of ultraviolet (UV) light for water disinfection has become increasingly popular due to on-going issues with drinking water and public health. Pulsed UV light has proved to be an effective form of inactivating a range of pathogens including parasite species. However, there are limited data available on the use of pulsed UV light for the disinfection of flowing water in the absence or presence of inorganic contaminants commonly found in water sources. Here, we report on the inactivation of test species including Bacillus endospores following pulsed UV treatment as a flow through system. Significant levels of inactivation were obtained for both retention times tested. The presence of inorganic contaminants iron and/or manganese did affect the rate of disinfection, predominantly resulting in an increase in the levels of inactivation at certain UV doses. The findings of this study suggest that pulsed UV light may provide a method of water disinfection as it successfully inactivated bacterial cells and bacterial endospores in the absence and presence of inorganic contaminants.

Effectiveness of organic and inorganic pigments for mass colouration of thermo-mechanical pulp used in wood–plastic composites

At present, to provide wood–plastic composites (WPC) with colouration and UV-protection, pigments are added in powder form or pre-dispersed in a polymer matrix (masterbatch) during compounding. Usually, the wood particles are not coloured prior to compounding, although this may improve the colour stability of the WPC. In this research project, two types of pigments were used to pre-colour thermo-mechanical pulp: an aqueous inorganic pigment preparation based on iron oxide and a water-based preparation of organic and inorganic pigments. Pre-coloured fibres were mixed with high-density polyethylene and maleic-anhydride grafted-PE in a kneading mixer and injection-moulded. As a reference, uncoloured fibres were mixed with pigments. Colour stability of the WPC was determined as ΔE* after 400 h of Xenon weathering. Pre-treatment of the fibres alone was not sufficient to improve colour stability of WPC. However, the use of fibres pre-treated with inorganic iron oxide pigments in combination with a pigment masterbatch to colour the polymer matrix resulted in a significant reduction of ΔE* compared to when either pre-coloured fibres only or uncoloured fibres plus pigment were used. The mixture of organic and inorganic pigments was less effective in improving colour stability than the application of inorganic pigments only. Flexural strength and modulus of elasticity of WPC with coloured fibres were slightly reduced compared to WPC with uncoloured fibres. Water uptake was higher for WPC with organic pigments than for WPC with inorganic pigments only. Fibre pre-colouration appears useful to obtain WPC with low colour change as a result of weathering.

Removal of organic and inorganic compounds from landfill leachate using reverse osmosis

The main objective of this work was to evaluate an effectiveness of removing organic and inorganic pollutants from landfill leachate in a long-term reverse osmosis (RO) study. Investigations were carried out during the first year of RO exploitation since February till September 2013. Over 20 parameters were analysed both in leachate and permeate samples. In the first 1-year operation, the treatment performance was feasible for most of analysed leachate pollutants. The average removal rate of chemical oxygen demand (COD), electro-conductivity, ammonia nitrogen (N-NH4 +), total inorganic nitrogen, cyanides (CN−), iron (Fe) and chlorides (Cl−) reached 97, 97.2, 98.7, 99, 93, 97.6 and 98 %, respectively. A smaller reduction rate—of 83 and 86 %—was obtained for sulphates (SO4 2−) and sulphides (S−), what is the result of sulphuric acid addition before treatment process in order to decline a pH to a value of 6.0–6.5. Boron was eliminated only by 81 % due to easy transportation through the membrane uncharged species of boric acid B(OH)3, which predominate in leachate. Average reduction of nitrites (NO2 −) and nitrates (NO3 −) was 63.8 %, which is the result of inhibition NO2 − oxidizers by nitrous acid and relatively low ratio of biochemical oxygen demand and COD (BOD/COD). The obtained permeate quality does not meet the Polish discharge standards for S−. It is also foreseen that the concentration of N-NH4 + in maturate leachate will increase in the next years.

PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; pollution in a megacity of southwest China: source apportionment and implication

Abstract. Daily PM2.5 (aerosol particles with an aerodynamic diameter of less than 2.5 μm) samples were collected at an urban site in Chengdu, an inland megacity in southwest China, during four 1-month periods in 2011, with each period in a different season. Samples were subject to chemical analysis for various chemical components ranging from major water-soluble ions, organic carbon (OC), element carbon (EC), trace elements to biomass burning tracers, anhydrosugar levoglucosan (LG), and mannosan (MN). Two models, the ISORROPIA II thermodynamic equilibrium model and the positive matrix factorization (PMF) model, were applied to explore the likely chemical forms of ionic constituents and to apportion sources for PM2.5. Distinctive seasonal patterns of PM2.5 and associated main chemical components were identified and could be explained by varying emission sources and meteorological conditions. PM2.5 showed a typical seasonality of waxing in winter and waning in summer, with an annual mean of 119 μg m−3. Mineral soil concentrations increased in spring, whereas biomass burning species elevated in autumn and winter. Six major source factors were identified to have contributed to PM2.5 using the PMF model. These were secondary inorganic aerosols, coal combustion, biomass burning, iron and steel manufacturing, Mo-related industries, and soil dust, and they contributed 37 ± 18, 20 ± 12, 11 ± 10, 11 ± 9, 11 ± 9, and 10 ± 12%, respectively, to PM2.5 masses on annual average, while exhibiting large seasonal variability. On annual average, the unknown emission sources that were not identified by the PMF model contributed 1 ± 11% to the measured PM2.5 mass. Various chemical tracers were used for validating PMF performance. Antimony (Sb) was suggested to be a suitable tracer of coal combustion in Chengdu. Results of LG and MN helped constrain the biomass burning sources, with wood burning dominating in winter and agricultural waste burning dominating in autumn. Excessive Fe (Ex-Fe), defined as the excessive portion in measured Fe that cannot be sustained by mineral dust, is corroborated to be a straightforward useful tracer of iron and steel manufacturing pollution. In Chengdu, Mo / Ni mass ratios were persistently higher than unity, and considerably distinct from those usually observed in ambient airs. V / Ni ratios averaged only 0.7. Results revealed that heavy oil fuel combustion should not be a vital anthropogenic source, and additional anthropogenic sources for Mo are yet to be identified. Overall, the emission sources identified in Chengdu could be dominated by local sources located in the vicinity of Sichuan, a result different from those found in Beijing and Shanghai, wherein cross-boundary transport is significant in contributing pronounced PM2.5. These results provided implications for PM2.5 control strategies.

Bulk AGET ATRP of methyl methacrylate using iron(iii) acetylacetonate as a catalyst

In this work, polymerization of methyl methacrylate (MMA) was successfully conducted by atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP) at 90 °C, using iron(III) acetylacetonate (Fe(acac)3) as a catalyst, ethyl alpha-bromophenylacetate (EBPA) as an initiator, ascorbic acid (AsAc) as a reducing agent and triphenyl phosphine (PPh3) as a ligand. The polymerization kinetics showed that the polymerization rate (the conversion reached up to 98.1% after 60 min) was much higher than that mediated by inorganic iron salts and it was affected by the feed of the iron catalyst. Moreover, the kinetic plots were linear, and the molecular weights of the resulting polymers with molecular weight distribution around 1.2, increased linearly with monomer conversions, indicating good features of “living”/controlled radical polymerizations. The end-functionality of the polymers was confirmed by 1H NMR spectroscopy and a chain extension experiment.

Deficiency of the ferrous iron transporter FeoAB is linked with metronidazole resistance in Bacteroides fragilis

Metronidazole is the most commonly used antimicrobial for Bacteroides fragilis infections and is recommended for prophylaxis of colorectal surgery. Metronidazole resistance is increasing and the mechanisms of resistance are not clear. A transposon mutant library was generated in B. fragilis 638R (BF638R) to identify the genetic loci associated with resistance to metronidazole. Thirty-two independently isolated metronidazole-resistant mutants had a transposon insertion in BF638R_1421 that encodes the ferrous transport fusion protein (feoAB). Deletion of feoAB resulted in a 10-fold increased MIC of metronidazole for the strain. The metronidazole MIC for the feoAB mutant was similar to that for the parent strain when grown on media supplemented with excess iron, suggesting that the increase seen in the MIC of metronidazole was due to reduced cellular iron transport in the feoAB mutant. The furA gene repressed feoAB transcription in an iron-dependent manner and disruption of furA resulted in constitutive transcription of feoAB, regardless of whether or not iron was present. However, disruption of feoAB also diminished the capacity of BF638R to grow in a mouse intraperitoneal abscess model, suggesting that inorganic ferrous iron assimilation is essential for B. fragilis survival in vivo. Selection for feoAB mutations as a result of metronidazole treatment will disable the pathogenic potential of B. fragilis and could contribute to the clinical efficacy of metronidazole. While mutations in feoAB are probably not a direct cause of clinical resistance, this study provides a key insight into intracellular metronidazole activity and the link with intracellular iron homeostasis.

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake.

Cyanobacteria are globally important primary producers that have an exceptionally large iron requirement for photosynthesis. In many aquatic ecosystems, the levels of dissolved iron are so low and some of the chemical species so unreactive that growth of cyanobacteria is impaired. Pathways of iron uptake through cyanobacterial membranes are now being elucidated, but the molecular details are still largely unknown. Here we report that the non-siderophore-producing cyanobacterium Synechocystis sp. PCC 6803 contains three exbB-exbD gene clusters that are obligatorily required for growth and are involved in iron acquisition. The three exbB-exbDs are redundant, but single and double mutants have reduced rates of iron uptake compared with wild-type cells, and the triple mutant appeared to be lethal. Short-term measurements in chemically well-defined medium show that iron uptake by Synechocystis depends on inorganic iron (Fe') concentration and ExbB-ExbD complexes are essentially required for the Fe' transport process. Although transport of iron bound to a model siderophore, ferrioxamine B, is also reduced in the exbB-exbD mutants, the rate of uptake at similar total [Fe] is about 800-fold slower than Fe', suggesting that hydroxamate siderophore iron uptake may be less ecologically relevant than free iron. These results provide the first evidence that ExbB-ExbD is involved in inorganic iron uptake and is an essential part of the iron acquisition pathway in cyanobacteria. The involvement of an ExbB-ExbD system for inorganic iron uptake may allow cyanobacteria to more tightly maintain iron homeostasis, particularly in variable environments where iron concentrations range from limiting to sufficient.

Characterization and source apportionment of aerosol light extinction in Chengdu, southwest China

To investigate aerosol properties in the Sichuan Basin of China, field aerosol sampling was carried out in Chengdu, China during four one-month periods, each in a different season in 2011. Aerosol scattering coefficient (bsp) at dry (RH<40%) and wet (40% < RH<90%) conditions and aerosol absorption coefficient (bap) were measured. Additionally, daily PM2.5 and PM10 samples were also collected. PM2.5 samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic and elemental carbon (OC and EC), trace elements, as well as anhydrosugar Levoglucosan (LG) and Mannosan (MN). A multiple linear regression analysis was applied to the measured dry bsp against (NH4)2SO4, NH4NO3, organic mass (OM), fine soil (FS), and coarse mass (CM, PM2.5–10), and to the measured bap against EC in all the four seasons to evaluate the impact of individual chemical components of PM2.5 and CM on aerosol light extinction (bext = bsp + bap). Mass scattering efficiency (MSE) and mass absorption efficiency (MAE) of the individual chemical components of PM2.5 were estimated based on seasonal regression equations and were then used for estimating bext. The annual bsp, bap and single scattering albedo (SSA) at dry conditions were 456 ± 237 Mm−1, 96 ± 48 Mm−1 and 0.82 ± 0.05, respectively. The annual average bsp at ambient conditions estimated through hygroscopic curve of aerosol (f(RH)) was 763 ± 415 Mm−1, which was 1.7 times of the dry bsp. The annual average SSA at ambient conditions also increased to 0.88 ± 0.04. The estimated dry bext was only 2 ± 9% higher than the measurements and the estimated ambient bext from individual chemical components was only 1 ± 10% lower, on an annual basis, than that estimated from using f(RH). Secondary inorganic aerosols, coal combustion, biomass burning, iron and steel industry, Mo-related industry, soil dust, and CM to bext were estimated to account for 41 ± 19%, 18 ± 12%, 14 ± 13%, 13 ± 11%, 5 ± 4%, 5 ± 7% and 4 ± 3%, respectively, of the estimated ambient bext.

The regeneration of highly bioavailable iron by meso‐ and microzooplankton

The micronutrient iron (Fe) is rapidly cycled in surface waters, and regenerated Fe supports much of the phytoplankton growth in open ocean waters. Meso‐ and microzooplankton grazing are both important mechanisms to regenerate Fe, but the chemical conditions in the respective digestive systems are different and might affect the bioavailability of Fe. We conducted radiotracer grazing experiments with the copepod Acartia tonsa or the heterotrophic dinoflagellate Oxyrrhis marina feeding on the diatom Thalassiosira pseudonana or the coccolithophore Emiliania huxleyi. Uptake of regenerated 55Fe by a separate T. pseudonana culture was compared to the uptake of inorganic Fe. Iron regenerated by A. tonsa was taken up 4‐ to 7‐fold faster than inorganic iron. In contrast, no difference was detected between the uptake rate of inorganic Fe and Fe regenerated by O. marina. Ingestion of different prey by A. tonsa revealed that Fe released during diatom digestion was taken up 1.8‐fold faster than Fe released from coccolithophore digestion. Digestive systems and the chemical makeup of the ingested prey are crucial in determining the bioavailability of regenerated Fe. Differences in pH and oxygen saturation between digestive vacuoles and guts may affect the speciation of regenerated Fe, and the release of ferrous Fe might contribute to the bioavailability of regenerated Fe. The ecological structure determines the importance of regenerated Fe for a particular ecosystem.

Addition of citrate to Acidithiobacillus ferrooxidans cultures enables precipitate-free growth at elevated pH and reduces ferric inhibition.

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotroph that is important in biomining and other biotechnological operations. The cells are able to oxidize inorganic iron, but the insolubility and product inhibition by Fe(3+) complicates characterization of these cultures. Here we explore the growth kinetics of A. ferrooxidans in iron-based medium in a pH range from 1.6 to 2.2. It was found that as the pH was increased from 1.6 to 2.0, the maintenance coefficient decreased while both the growth kinetics and maximum cell yield increased in the precipitate-free, low Fe(2+) concentration medium. In higher iron media a similar trend was observed at low pH, but the formation of precipitates at higher pH (2.0) hampered cell growth and lowered the specific growth rate and maximum cell yield. In order to eliminate ferric precipitates, chelating agents were introduced into the medium. Citric acid was found to be relatively non-toxic and did not appear to interfere with iron oxidation at a maximum concentration of 70 mM. Inclusion of citric acid prevented precipitation and A. ferrooxidans growth parameters resumed their trends as a function of pH. The addition of citrate also decreased the apparent substrate saturation constant (KS ) indicating a reduction in the competitive inhibition of growth by ferric ions. These results indicate that continuous cultures of A. ferrooxidans in the presence of citrate at elevated pH will enable enhanced cell yields and productivities. This will be critical as these cells are used in the development of new biotechnological applications such as electrofuel production.

Development and characterization of Hephaestin knockdown Caco‐2 cells (818.13)

Intestinal transport of inorganic iron has been intensively studied. Ferric iron is reduced, possibly by duodenal cytochrome b (Dcytb), and transported into cells by divalent metal‐ion transport 1 (Dmt1). Ferrous iron is exported from enterocytes via ferroportin 1 (Fpn1) and is then oxidized prior to binding to transferrin. The efflux step, involving the export‐oxidation functional couple, is the rate‐limiting step in iron absorption. Although an iron oxidase has been discovered (Heph), it is likely that other oxidases also exist. The current study was thus designed to assess the necessity of Heph for iron transport using the Caco‐2 cell model. Caco‐2 cells, which differentiate in post‐confluent culture, express an inducible, vectorial iron transport system, faithfully recapitulating mammalian iron absorption. Heph was effectively silenced in Caco‐2 cells using shRNA technology. A control cell line was also established with negative‐control shRNA transfected cells. Heph KD cells grew normally and were visually indistinguishable from control cells. Gene expression studies showed that Dcytb (~55%) and Dmt1 (~25%) mRNA expression was decreased, while Fpn1 expression was unaffected. Heph protein levels were significantly reduced (&lt;90%) in cytosolic and membrane fractions of the KD cells. Ferrous iron oxidation measurements, using a transferrin‐coupled assay, showed that Heph KD had very little effect on membrane and cytosolic ferroxidase (FOX) activity. Additional studies showed for the first time that Heph was detected in early and late endosomes isolated from Caco‐2 cells, fractions in which Rab7 was also detected (an endosomal marker). This investigation has thus provided further evidence that Heph is not the sole FOX in mammalian intestinal epithelial cells.Grant Funding Source: Supported by NIH Grant, 2R01DK074867‐07A1

Comparative Study of the Pharmacokinetics of Inorganic and Organic Iron Compounds in Broiler Chickens

Abstract The pharmacokinetics of ferrous methionate and ferrous sulphate was investigated in broiler chickens after intravenous injection and crop intubation. The iron compounds were injected intravenously in v. brachialis. After a 20-day “wash-out” period the ferrous methionate and ferrous sulphate were administered again by an elastic silicone tube into the crop. The serum concentrations of the iron were determined using a bioanalyser. Two pharmacokinetic approaches were used - compartmental and non-compartmental analysis. After i.v. injection we found statistically significantly longer and better distribution of the iron contained in the ferrous methionate compared to the ferrous sulphate. The АUC0→∞ was statistically significantly higher in the ferrous methionate. In the alimentary tract of broiler chickens, ferrous methionate was absorbed more rapidly than ferrous sulfate. It was also distributed at a higher volume as compared to the ferrous sulfate