Facile and greener hydrothermal honey-based synthesis of Fe3O 4/Au core/shell nanoparticles for drug delivery applications

In the present research, we report a greener, faster, and low-cost synthesis of gold-coated iron oxide nanoparticles (Fe₃O₄/Au-NPs) by different ratios (1:1, 2:1, and 3:1 molar ratio) of iron oxide and gold with natural honey (0.5% w/v) under hydrothermal conditions for 20 minutes. Honey was used as the reducing and stabilizing agent, respectively. The nanoparticles were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), vibrating sample magnetometer (VSM), and fourier transformed infrared spectroscopy (FT-IR). The XRD analysis indicated the presence of Fe₃O₄/Au-NPs, while the TEM images showed the formation of Fe₃O₄/Au-NPs with diameter range between 3.49 nm and 4.11 nm. The VSM study demonstrated that the magnetic properties were decreased in the Fe₃O₄/Au-NPs compared with the Fe₃O₄-NPs. The cytotoxicity threshold of Fe₃O₄/Au-NPs in the WEHI164 cells was determined by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. It was demonstrated no significant toxicity in higher concentration up to 140.0 ppm which can become the main candidates for biological and biomedical applications, such as drug delivery.     

Effects of electron donors and acceptors on anaerobic reduction of azo dyes by <Emphasis Type="Italic">Shewanella decolorationis</Emphasis> S12

Shewanella decolorationis S12 was able to reduce various azo dyes in a defined medium with formate, lactate, and pyruvate or H₂ as electron donors under anaerobic conditions. Purified membranous, periplasmic, and cytoplasmic fractions from strain S12 analyzed, respectively, only membranous fraction was capable of reducing azo dye in the presence of electron donor, indicating that the enzyme system for anaerobic azoreduction was located on cellular membrane. Respiratory inhibitor Cu²⁺, dicumarol, stigmatellin, and metyrapone inhibited anaerobic azoreduction by purified membrane fraction, suggesting that the bacterial anaerobic azoreduction by strain S12 was a biochemical process that oxidizes the electron donors and transfers the electrons to the acceptors through a multicompound system related to electron transport chain. Dehydrogenases, cytochromes, and menaquinones were essential electron transport components for the azoreduction. The electron transport process for azoreduction was almost fully inhibited by O₂, 6 mM of , and 0.9 mM of , but not by 10 mM of Fe³⁺. The inhibition may be a result from the competition for electrons from electron donors. These findings impact on the understanding of the mechanism of bacterial anaerobic azoreduction and have implication for improving treatment methods of wastewater contaminated by azo dyes.     

Respiration and Growth of Shewanella decolorationis S12 with an Azo Compound as the Sole Electron Acceptor

The ability of Shewanella decolorationis S12 to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory azoreduction was investigated. This microorganism can reduce a variety of azo dyes by use of formate, lactate, pyruvate, or H₂ as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0 × 10⁷ cells per ml after compete reduction of 2.0 mM amaranth in a defined medium. This was accompanied by a stoichiometric consumption of 4.0 mM formate over time when amaranth and formate were supplied as the sole electron acceptor and donor, respectively, suggesting that microbial azoreduction is an electron transport process and that this electron transport can yield energy to support growth. Purified membranous, periplasmic, and cytoplasmic fractions from S12 were analyzed, but only the membranous fraction was capable of reducing azo dyes with formate, lactate, pyruvate, or H₂ as the electron donor. The presence of 5 μM Cu²⁺ ions, 200 μM dicumarol, 100 μM stigmatellin, and 100 μM metyrapone inhibited anaerobic azoreduction activity by both whole cells and the purified membrane fraction, showing that dehydrogenases, cytochromes, and menaquinone are essential electron transfer components for azoreduction. These results provide evidence that the microbial anaerobic azoreduction is linked to the electron transport chain and suggest that the dissimilatory azoreduction is a form of microbial anaerobic respiration. These findings not only expand the number of potential electron acceptors known for microbial energy conservation but also elucidate the mechanisms of microbial anaerobic azoreduction.     

纳米铁氧化物对Pelotomaculum schinkii培养系丙酸厌氧降解产甲烷的影响

微生物能利用导电材料进行电子传递,提高种间电子传递效率。铁基纳米导电物质可以加速土壤及厌氧消化系统中微生物间的种间电子传递,促进有机废弃物的产甲烷过程。前期获得了厌氧丙酸富集培养系,互营丙酸氧化菌（Pelotomaculum schinkii）在培养系中占优势,本研究考察了10~4 000 mg/L 纳米铁氧化物对丙酸降解产甲烷过程的作用及微生物的影响。结果表明,低浓度的铁基纳米材料对丙酸降解有一定的促进作用,而高浓度会抑制产甲烷：10~1 000 mg/L纳米Fe₃O₄对产甲烷无明显影响,1 500~4 000 mg/L最大产甲烷速率抑制了26%~80%,延滞期增加了174%~222%;10~200 mg/L纳米Fe₂O₃使最大产甲烷速率提高了21%~29%,1 500~4 000 mg/L最大产甲烷速率抑制了48%~58%,延滞期增加了29%~85%。微生物群落解析结果表明,与对照相比,10~1 000 mg/L纳米Fe₂O₃使P. schinkii相对丰度略有增加,而4 000 mg/L纳米₃O₄/Fe₂O₃使P. schinkii的相对丰度下降了70.7%和55.9%,说明高浓度纳米铁氧化物会抑制P. schinkii的活性,导致丙酸降解及产甲烷速率降低。     

Reduction of Soluble and Insoluble Iron Forms by Membrane Fractions of Shewanella oneidensis Grown under Aerobic and Anaerobic Conditions

The effect of iron substrates and growth conditions on in vitro dissimilatory iron reduction by membrane fractions of Shewanella oneidensis MR-1 was characterized. Membrane fractions were separated by sucrose density gradients from cultures grown with O₂, fumarate, and aqueous ferric citrate as the terminal electron acceptor. Marker enzyme assays and two-dimensional gel electrophoresis demonstrated the high degree of separation between the outer and cytosolic membrane. Protein expression pattern was similar between chelated iron- and fumarate-grown cultures, but dissimilar for oxygen-grown cultures. Formate-dependent ferric reductase activity was assayed with citrate-Fe³⁺, ferrozine-Fe³⁺, and insoluble goethite as electron acceptors. No activity was detected in aerobic cultures. For fumarate and chelated iron-grown cells, the specific activity for the reduction of soluble iron was highest in the cytosolic membrane. The reduction of ferrozine-Fe³⁺ was greater than the reduction of citrate-Fe³⁺. With goethite, the specific activity was highest in the total membrane fraction (containing both cytosolic and outer membrane), indicating participation of the outer membrane components in electron flow. Heme protein content and specific activity for iron reduction was highest with chelated iron-grown cultures with no heme proteins in aerobically grown membrane fractions. Western blots showed that CymA, a heme protein involved in iron reduction, expression was also higher in iron-grown cultures compared to fumarate- or aerobic-grown cultures. To study these processes, it is important to use cultures grown with chelated Fe³⁺ as the electron acceptor and to assay ferric reductase activity using goethite as the substrate.     

Novel and efficient method for immobilization and stabilization of β-d-galactosidase by covalent attachment onto magnetic Fe3O4–chitosan nanoparticles

A novel and efficient immobilization of β-d-galactosidase from Aspergillus oryzae has been developed by using magnetic Fe₃O₄–chitosan (Fe₃O₄–CS) nanoparticles as support. The magnetic Fe₃O₄–CS nanoparticles were prepared by electrostatic adsorption of chitosan onto the surface of Fe₃O₄ nanoparticles made through co-precipitation of Fe²⁺ and Fe³⁺. The resultant material was characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry and thermogravimetric analysis. β-d-Galactosidase was covalently immobilized onto the nanocomposites using glutaraldehyde as activating agent. The immobilization process was optimized by examining immobilized time, cross-linking time, enzyme concentration, glutaraldehyde concentration, the initial pH values of glutaraldehyde and the enzyme solution. As a result, the immobilized enzyme presented a higher storage, pH and thermal stability than the soluble enzyme. Galactooligosaccharide was formed with lactose as substrate by using the immobilized enzyme as biocatalyst, and a maximum yield of 15.5% (w/v) was achieved when about 50% lactose was hydrolyzed. Hence, the magnetic Fe₃O₄–chitosan nanoparticles are proved to be an effective support for the immobilization of β-d-galactosidase.     

Investigation of roles of divalent cations in Shewanella oneidensis pellicle formation reveals unique impacts of insoluble iron

Background

Bacteria adopt a variety of lifestyles in their natural habitats and can alternate among different lifestyles in response to environmental changes. At high cell densities, bacteria can form extracellular matrix encased cell population on submerged tangible surfaces (biofilms), or at the air–liquid interface (pellicles). Compared to biofilm, pellicle lifestyle allows for better oxygen access, but is metabolically more costly to maintain. Further understanding of pellicle formation and environmental cues that influence cellular choices between these lifestyles will definitely improve our appreciation of bacterial interaction with their environments.

Methods

Shewanella oneidensis cells were cultured in 24-well plates with supplementation of varied divalent cations, and pellicles formed under such conditions were evaluated. Mutants defective in respiration of divalent cations were used to further characterize and confirm unique impacts of iron.

Results and conclusions

Small amount of Fe^2 + was essential for pellicle formation, but presence of over-abundant iron (0.3 mM Fe^2 + or Fe^3 +) led to pellicle disassociation without impairing growth. Such impacts were found due to S. oneidensis-mediated formation of insoluble alternative electron acceptors (i.e., Fe₃O₄) under physiologically relevant conditions. Furthermore, we demonstrated that cells preferred a lifestyle of forming biofilm and respiring on such insoluble electron acceptors under tested conditions, even to living in pellicles.

General significance

Our finding suggests that bacterial lifestyle choice involves balanced evaluation of multiple aspects of environmental conditions, and yet-to-be-characterized signaling mechanism is very likely underlying such processes.     

Improved degradation of lignocellulosic biomass pretreated by Fenton-like reaction using Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles

The ability of Fe₃O₄ Fenton-like reaction to produce glucose from lignocellulosic biomass was investigated. Fe₃O₄ magnetite nanoparticles were chemically synthesized from iron salts (a mixture of 1 M FeCl₂ and 2M FeCl₃) using an ammonia solution (30% NH₄OH). The synthesized Fe₃O₄ nanoparticles were further characterized by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. Reed stems and rice straw biomasses pretreated with optimized Fenton-like reagents (Fe₃O₄ and H₂O₂) increased glucose production by 177 and 87%, respectively, compared to the control without the catalysts.     

Intracellular carbonic anhydrase activities in Dunaliella tertiolecta (Butcher) and Chlamydomonas reinhardtii (Dangeard) in relation to inorganic carbon concentration during growth: further evidence for the existence of two distinct carbonic anhydrases associated with the chloroplasts

Using mass-spectrometric measurements of ¹⁸O exchange from ¹³C¹⁸O₂ intracellular carbonic anhydrase (CA) activity was investigated in the unicellular green algae Dunaliella tertiolecta and Chlamydomonas reinhardtii which were either grown on air enriched with 5% CO₂ (high-C_i cells) or on air (low-C_i cells). In D. tertiolecta high- and low-C_i cells had detectable levels of internal CA activity when measured under in-vivo conditions and this activity could be split up into three distinct forms. One CA was not associated with the chloroplasts, while two isozymes were found to be located within the plastids. The activities of all intracellular CAs were always about twofold higher in low than in high-C_i cells of D. tertiolecta and the chloroplastic enzymes were completely induced within 4 h of adaptation to air. One of the chloroplastic CAs was found to be soluble the other was insoluble. In addition to the physical differences, MgSO₄ in vitro caused a more than twofold stimulation of the soluble activity while the insoluble form of CA remained rather unaffected. In C. reinhardtii, MgSO₄ increased the soluble CA activity by 346% and the concentration of MgSO₄ required for half-maximum stimulation was between 10 and 15 mM. Again, the insoluble CA activity was not affected by MgSO₄. Furthermore, the soluble isoenzyme was considerably more sensitive to ethoxyzolamide, a potent inhibitor of CA, than the insoluble enzyme. The concentration of inhibitor causing 50% inhibition of soluble CA activity was 110 and 85 μM ethoxyzolamide for D. tertiolecta and C. reinhardtii, respectively. From these data we conclude that the two chloroplast-associated CAs are distinct enzymes.     

Ability of marine eukaryotic red tide microalgae to utilize insoluble iron

Iron is an essential trace metal and a limiting factor for microalgal growth, but bioavailable dissolved iron concentrations in seawater are low. Microalgal blooms have frequently occurred in coastal areas under such iron limitation accompanied by mass mortalities of fish and bivalves. Their massive growth despite physiological iron-deficiency has long been an enigma, because most of them cannot grow in chemically defined artificial media. We developed a feasible artificial medium for the culture of many species of red tide microalgae modified for investigation of iron utilization. Here, we report on the ability of marine eukaryotic red tide microalgae to utilize insoluble iron. Some microalgal species could utilize particulate FePO₄ and FeS for growth. Particulate FePO₄ was available for the growth of the raphidophyte Heterosigma akashiwo, the dinoflagellate Heterocapsa triquetra and the diatom Ditylum brightwellii. The dinoflagellates Heterocapsa circularisquama and Karenia mikimotoi, and the cryptophyte Rhodomonas ovalis utilized both particulate FePO₄ and particulate FeS for growth. In contrast, particulate FeO(OH) and Fe₂O₃ did not support the growth of any of the red tide microalgae examined. Except for Chattonella species (Raphidophyceae), the growth of red tide microalgae were confirmed in the medium with very easily soluble FeCl₃ added. The order of bioavailability of tested iron-source species were Fe–EDTA > FeCl₃ > FePO₄ > FeS > FeO(OH), Fe₂O₃ for most of microalgae examined, although for H. circularisquama the utilization of FeCl₃ was higher than that of Fe–EDTA. The results suggest that red tide microalgae show different patterns of specific strategies for the utilization of various iron sources. The occurrence of red tides in coastal areas may depend on the combination of microalgal species and insoluble iron species present.     

Electron acceptor availability alters carbon and energy metabolism in a thermoacidophile

The thermoacidophilic Acidianus strain DS80 displays versatility in its energy metabolism and can grow autotrophically and heterotrophically with elemental sulfur (S°), ferric iron (Fe³⁺) or oxygen (O₂) as electron acceptors. Here, we show that autotrophic and heterotrophic growth with S° as the electron acceptor is obligately dependent on hydrogen (H₂) as electron donor; organic substrates such as acetate can only serve as a carbon source. In contrast, organic substrates such as acetate can serve as electron donor and carbon source for Fe³⁺ or O₂ grown cells. During growth on S° or Fe³⁺ with H₂ as an electron donor, the amount of CO₂ assimilated into biomass decreased when cultures were provided with acetate. The addition of CO₂ to cultures decreased the amount of acetate mineralized and assimilated and increased cell production in H₂/Fe³⁺ grown cells but had no effect on H₂/S° grown cells. In acetate/Fe³⁺ grown cells, the presence of H₂ decreased the amount of acetate mineralized as CO₂ in cultures compared to those without H₂. These results indicate that electron acceptor availability constrains the variety of carbon sources used by this strain. Addition of H₂ to cultures overcomes this limitation and alters heterotrophic metabolism.     

Fe3O4-PEG-CD56/Avastin@Ce6纳米探针的合成及细胞MR成像初步研究

目的:探讨Fe_3O_4-PEG-CD56/Avastin@Ce6靶向探针与NK92细胞的结合能力并进行细胞体外MRI成像。方法:制备Fe_3O_4-PEG-CD56/Avastin@Ce6纳米探针,对合成的材料进行表征。应用凋亡试剂盒测定不同浓度的材料对NK92的细胞毒性,通过流式细胞术分析纳米材料与NK92细胞的结合能力和应用MRI对细胞进行体外成像并分析其T2信号强度的改变。结果:合成的纳米探针具有较好的生物相容性,且对NK92细胞的影响较小,不同浓度下细胞凋亡水平基本一致,与NK92细胞结合的材料随浓度的增加而逐渐增加。MRI检查提示不同浓度探针孵育的NK92细胞T2加权像(T2WI)的信号均降低。结论:Fe_3O_4-PEG-CD56/Avastin@Ce6探针对NK92细胞具有靶向性,3.0 T MR扫描仪可对其进行体外监测。     

Effects of various iron supply on oxidative stress development and ferritin formation in the common ice plants

Mesembryanthemum crystallinum L. plants were grown from seeds in perlite. At the age of 4 weeks (juvenile plants) or 6 weeks (adult plants), they were transferred on nutrient media with different Fe³⁺ content brought in as Fe₂(SO₄)₃—EDTA complex (pH 6.0): control, iron deficit, and iron “excess”. Adult plants grown in media differing in iron content were subjected to salinity (300 mM NaCl) during the last 8 days of growth. Biochemical analyses were performed after plant fixation in liquid nitrogen; simultaneously, the samples for electron microscopy were taken. Different content of available Fe³⁺ in medium, especially under salinity conditions, changed sharply the content of chlorophyll and proline, the rate of lipid peroxidation, the level of H₂O₂, the activities of antioxidant enzymes in the leaves and roots, the number and sizes of plastoglobules, and ferritin formation in plastids. Joint action of salinity and iron deficit enhanced oxidative stress development, whereas iron excess hampered oxidative reaction development, reduced the rate of lipid peroxidation, and increased the chlorophyll content. At iron excess, plastoglobule lysis in plastids did not occur, their number and sizes increased, and ferritin deposits appeared, whereas the latter were absent at iron deficit.     

An Iron-Messenger System - A Hypothesis

Iron in the free ionic state is very reactive as it generates and reacts with free radicals of the type HO, LO, LOO', O^?₂ and C. These are highly reactive species and participate in reactions that are mostly deleterious to cell components, including DNA, proteins and lipids. In association with a complexing agent such as bleomycin, Fe²⁺ degrades DNA into soluble nucleotides'. In the presence of oxygen and a reducing agent, DTT, Fe²⁺ inacativates enzymes by peptide bond cleavage². Chelated to ADP, Fe²⁺ promotes peroxidation of polyunsaturated fatty acids and breakdown of membranes³. These do not occur in normal cells as they are kept under check by antioxidant devices, and more importantly by keeping free iron concentration low.     

Dynamics of Iron Uptake and Fe3O4 Biomineralization during Aerobic and Microaerobic Growth of Magnetospirillum gryphiswaldense

Iron uptake and magnetite (Fe₃O₄) crystal formation could be studied in the microaerophilic magnetic bacterium Magnetospirillum gryphiswaldense by using a radioactive tracer method for iron transport and a differential light-scattering technique for magnetism. Magnetite formation occurred only in a narrow range of low oxygen concentration, i.e., 2 to 7 μM O₂ at 30°C. Magnetic cells stored up to 2% iron as magnetite crystals in intracytoplasmic vesicles. This extraordinary uptake of iron was coupled tightly to the biomineralization of up to 60 magnetite crystals with diameters of 42 to 45 nm.     

The lactate-dependent enhancement of hydroxyl radical generation by the Fenton reaction

The effect of lactic acid (lactate) on Fenton based hydroxyl radical (^·OH) production was studied by spin trapping, ESR, and fluorescence methods using DMPO and coumarin-3-carboxylic acid (3-CCA) as the ^·OH traps respectively. The ^·OH adduct formation was inhibited by lactate up to 0.4mM (lactate/iron stoichiometry = 2) in both experiments, but markedly enhanced with increasing concentrations of lactate above this critical concentration. When the H₂O₂ dependence was examined, the DMPO-OH signal was increased linearly with H₂O₂ concentration up to 1 mM and then saturated in the absence of lactate. In the presence of lactate, however, the DMPO-OH signal was increased further with higher H₂O₂ concentration than 1 mM, and the saturation level was also increased dependent on lactate concentration. Spectroscopic studies revealed that lactate forms a stable colored complex with Fe³⁺ at lactate/Fe³⁺ stoichiometry of 2, and the complex formation was strictly related to the DMPO-OH formation. The complex formation did not promote the H₂O₂ mediated Fe³⁺ reduction. When the Fe³⁺-lactate (1:2) complex was reacted with H₂O₂, the initial rate of hydroxylated 3-CCA formation was linearly increased with H₂O₂ concentrations. All the data obtained in the present experiments suggested that the Fe³⁺-lactate (1:2) complex formed in the Fenton reaction system reacts directly with H₂O₂ to produce additional ^·OH in the Fenton reaction by other mechanisms than lactate or lactate/Fe³⁺ mediated promotion of Fe³⁺/Fe²⁺ redox cycling.     

Competitive Inhibition of Ferrous Iron Oxidation by Thiobacillus ferrooxidans by Increasing Concentrations of Cells

The oxidation of ferrous iron (Fe²⁺) to ferric iron (Fe³⁺) with dioxygen (O₂) by various strains of Thiobacillus ferrooxidans was studied by measuring the rate of O₂ consumption at various Fe²⁺ concentrations and cell concentrations. The apparent K_m values for Fe²⁺ remained constant at different cell concentrations of laboratory strains ATCC 13661 and ATCC 19859 but increased with increasing cell concentrations of mine isolates SM-4 and SM-5. The latter results are explained by the competitive inhibition of the Fe²⁺-binding site of a cell by other cells in the reaction mixture. Possible mechanisms involving cell surface properties are discussed.     

A Bacterial Iron Exporter for Maintenance of Iron Homeostasis

Nutritional iron acquisition by bacteria is well described, but almost nothing is known about bacterial iron export even though it is likely to be an important homeostatic mechanism. Here, we show that Bradyrhizobium japonicum MbfA (Blr7895) is an inner membrane protein expressed in cells specifically under high iron conditions. MbfA contains an N-terminal ferritin-like domain (FLD) and a C-terminal domain homologous to the eukaryotic vacuolar membrane Fe²⁺/Mn²⁺ transporter CCC1. An mbfA deletion mutant is severely defective in iron export activity, contains >2-fold more intracellular iron than the parent strain, and displays an aberrant iron-dependent gene expression phenotype. B. japonicum is highly resistant to iron and H₂O₂ stresses, and MbfA contributes substantially to this as determined by phenotypes of the mbfA mutant strain. The N-terminal FLD was localized to the cytoplasmic side of the inner membrane. Substitution mutations in the putative iron-binding amino acid residues E20A and E107A within the N-terminal FLD abrogate iron export activity and stress response function. Purified soluble FLD oxidizes ferrous iron (Fe²⁺) to incorporate ferric iron (Fe³⁺) in a 2:1 iron:protein ratio, which does not occur in the E20A/E107A mutant. The FLD fragment is a dimer in solution, implying that the MbfA exporter functions as a dimer. MbfA belongs to a protein family found in numerous prokaryotic genera. The findings strongly suggest that iron export plays an important role in bacterial iron homeostasis.     

Singlet Oxygen and Other Reactive Oxygen Species are Involved in Regulation of Release of Iron-Binding Chelators from Scenedesmus cells

Freshly-added iron only slightly affected the growth of iron-sufficient cells of the green alga Scenedesmus incrassatulus Bohl, strain R-83, but induced accumulation of malondialdehyde (MDA) in cells and excretion of MDA in the medium. These effects were stronger in response to Fe²⁺ as compared to Fe³⁺, but Fe³⁺ induced the release of more iron-binding chelators from these cells than Fe²⁺. Fe³⁺ added either in dark or in light induced release of equal concentrations of iron-complexing agents, part of which formed strong chelates with iron in the medium. Exogenously added hydrogen peroxide inhibited iron-induced release of chelators but the effect was removed by addition of the hydroxyl radical scavenger dimethylsulfoxide (DMSO). Malondialdehyde also inhibited the release of chelators. Release of chelators was induced in the absence of iron salts by photoexcited chlorophyll (Chl). The Chl-induced release was efficiently inhibited by singlet oxygen scavengers such as dimethylfuran, -carotene, sodium azide and vitamin B₆, and stimulated in D₂O or DMSO. Exogenously added catalase inhibited the release more than added superoxide dismutase. The Fe³-induced release of chelators was also inhibited by scavengers of singlet oxygen, but was not affected by sodium azide and by ethanol. Hence both H₂O₂ and singlet oxygen were involved in induction of chelator release in the absence of iron in light. The induction of chelator release by iron in dark involved H₂O₂, but not singlet oxygen.     

Interaction between uranium and the cytochrome c 3 of Desulfovibrio desulfuricans strain G20

Cytochrome c₃ of Desulfovibrio desulfuricans strain G20 is an electron carrier for uranium (VI) reduction. When D. desulfuricans G20 was grown in medium containing a non-lethal concentration of uranyl acetate (1 mM), the rate at which the cells reduced U(VI) was decreased compared to cells grown in the absence of uranium. Western analysis did not detect cytochrome c₃ in periplasmic extracts from cells grown in the presence of uranium. The expression of this predominant tetraheme cytochrome was not detectably altered by uranium during growth of the cells as monitored through a translational fusion of the gene encoding cytochrome c₃ (cycA) to lacZ. Instead, cytochrome c₃ protein was found tightly associated with insoluble U(IV), uraninite, after the periplasmic contents of cells were harvested by a pH shift. The association of cytochrome c₃ with U(IV) was interpreted to be non-specific, since pure cytochrome c₃ adsorbed to other insoluble metal oxides, including cupric oxide (CuO), ferric oxide (Fe₂O₃), and commercially available U(IV) oxide.An erratum to this article can be found at