Ecological succession among iron-oxidizing bacteria

Despite over 125 years of study, the factors that dictate species dominance in neutrophilic iron-oxidizing bacterial (FeOB) communities remain unknown. In a freshwater wetland, we documented a clear ecological succession coupled with niche separation between the helical stalk-forming Gallionellales (for example, Gallionella ferruginea) and tubular sheath-forming Leptothrix ochracea. Changes in the iron-seep community were documented using microscopy and cultivation-independent methods. Quantification of Fe-oxyhydroxide morphotypes by light microscopy was coupled with species-specific fluorescent in situ hybridization (FISH) probes using a protocol that minimized background fluorescence caused by the Fe-oxyhydroxides. Together with scanning electron microscopy, these techniques all indicated that Gallionellales dominated during early spring, with L. ochracea becoming more abundant for the remainder of the year. Analysis of tagged pyrosequencing reads of the small subunit ribosomal RNA gene (SSU rRNA) collected during seasonal progression supported a clear Gallionellales to L. ochracea transition, and community structure grouped according to observed dominant FeOB forms. Axis of redundancy analysis of physicochemical parameters collected from iron mats during the season, plotted with FeOB abundance, corroborated several field and microscopy-based observations and uncovered several unanticipated relationships. On the basis of these relationships, we conclude that the ecological niche of the stalk-forming Gallionellales is in waters with low organic carbon and steep redoxclines, and the sheath-forming L. ochracea is abundant in waters that contain high concentrations of complex organic carbon, high Fe and Mn content and gentle redoxclines. Finally, these findings identify a largely unexplored relationship between FeOB and organic carbon.     

Removal of Cr6+ from groundwater using zero-valence iron in the laboratory

Abstract

In this paper, we describe a series of laboratory experiments which quantify the rate of Cr⁶⁺ reduction by Fe⁰. The main goal of these experiments was to determine the removal efficiency of Cr⁶⁺ by iron. The results indicate that Fe⁰ reduces Cr⁶⁺ to Cr³⁺ under alkaline and slightly acidic conditions. The removal efficiency rises with an increase of the initial concentration of Cr⁶⁺ (1 mg/L to 10 mg/L) when the quantity of Fe⁰ is stable. The removal efficiency increases as the quantity of Fe⁰ is raised when other conditions are constant. The removal efficiency would not be affected by other inorganic ions unless they were present at very high concentrations. When the initial concentration Cr⁶⁺ is 10mg/L and pH is 6.5–7.7, the final concentration of Cr⁶⁺ in effluent is less than 0.05 mg/L and the total Fe is less than 0.3 mg/L in effluent.     

Homocysteine Induces Iron-Catalyzed Lipid Peroxidation of Low-Density Lipoprotein that is Prevented by Alpha-Tocopherol

Homocystinuria is an inborn error of methionine metabolism that is characterized by the premature development of arteriosclerosis. As one of the major factors in the pathogenesis of arteriosclerosis, modification of low-density lipoprotein (LDL) has received widespread attention by many investigators. In this study, to elucidate the relationship between elevated homocysteine levels and premature arteriosclerosis, we investigated the role of homocysteine in the iron-catalyzed oxidative modification of LDL. When LDL isolated from a healthy subject was incubated with homocysteine and ferric ion, a gradual decrease of polyunsaturated fatty acids (PUFA), formation of thiobarbituric acid-reactive substances (TBARS) and fluorescent substances, and the fragmentation of apoprotein B (apoB) were observed. The extent of oxidative modification was dependent on the concentration of homocysteine. Modification of LDL was suppressed until the remaining α-tocopherol concentration reached a critical level. When the α-tocopherol content of LDL was increased by 2.6-fold, both the formation of TBARS and the fragmentation of apoB were suppressed. These results suggest that homocysteine might promote iron-catalyzed oxidation of LDL and imply its role for the development of premature arteriosclerosis.     

TonB protein and energy transduction between membranes

TonB protein couples cytoplasmic membrane electrochemical potential to active transport of iron-siderophore complexes and vitamin B12 through high-affinity outer membrane receptors of Gram-negative bacteria. The mechanism of energy transduction remains to be determined, but important concepts have already begun to emerge. Consistent with its function, TonB is anchored in the cytoplasmic membrane by its uncleaved amino terminus while largely occupying the periplasm. Both the connection to the cytoplasmic membrane and the amino acid sequences of the anchor are essential for activity. TonB directly associates with a number of envelope proteins, among them the outer membrane receptors and cytoplasmic membrane protein ExbB. ExbB and TonB interact through their respective transmembrane domains. ExbB is proposed to recycle TonB to an active conformation following energy transduction to the outer membrane. TonB most likely associates with the outer membrane receptors through its carboxy terminus, which is required for function. In contrast, the novel prolinerich region of TonB can be deleted without affecting function. A model that incorporates this information, as well as tempered speculation, is presented.     

Purification and chemical characterization of staphyloferrin B,a hydrophilic siderophore from staphylococci

This paper describes the chemical characterization of staphyloferrin B, a new complexone type siderophore isolated from low iron cultures of Staphylococcus hyicus DSM 20459. Purification of the very hydrophilic metabolite was achieved by anion exchange high performance liquid chromatography HPLC. Mass spectrometry showed a molecular mass of 448 amu. Hydrolysis with 8 mHCl revealed the presence of l-2,3-diaminopropionic acid, citrate, ethylenediamine and succinic semialdehyde. The connections between the four building blocks were determined by two-dimensional nuclear magnetic resonance measurements. UV/Vis and circular dichroism spectra are consistent with the proposed structure, which could also be confirmed by precursor feeding. The siderophore activity of staphyloferrin B was demonstrated by iron transport measurements.     

Characterization of three iron ferredoxins by microwave power saturation

We have measured the electronic spin lattice relaxation time T1 in the temperature range 4 K-10 K, by microwave power saturation on the 3Fe ferredoxins from Desulfovibrio gigas and Azotobacter vinelandii. The comparison with the results previously obtained on other iron sulfur proteins emphasizes the particularly fast relaxing properties of the E.P.R. signal in 3Fe ferredoxins. These results support the models of the active site which predict very low lying excited levels.     

Modification of the in vitro Cytotoxicity of Hydrogen Peroxide by Iron Complexes

The effect of a range of iron chelates on the cytotoxicity of H₂O₂ was studied on a mammalian epithelial cell line. Iron complexes which were internalised enhanced the cytotoxicity of H₂O₂ measured by delayed thymidine incorporation. Iron complexed to 8-hydroxyquinoline (Fe/8-HQ) potentiated the cytotoxicity of 50 µM by 38% and Fe/dextran by 23%. Pre-exposure of cells to Fe/dextran at 4°C did not result in any potentiation of H₂O₂-induced cytotoxicity which we ascribe to failure of the Fe/dextran to be endocytosed at low temperature. Iron complexes which are slowly taken up or remain extracellular protected the cells from H₂O₂-induced cytotoxicity. Thus, Fe/EDTA inhibited the cytotoxicity of 50 µM H₂O₂ by 33%; Fe/ADP by 80% and Fe/ATP by 88%, suggesting mutual extracellular detoxification.     

Bacterial Associations with Weathering Minerals at the Regolith-Bedrock Interface,Luquillo Experimental Forest,Puerto Rico

Microbe-mineral associations in regolith overlying granodiorite bedrock (4.6–4.9 m depth) from the Luquillo Experimental Forest, Puerto Rico, were imaged with confocal scanning laser microscopy at a novel scale of 400X magnification. After adding BacLight? stain, proportionally more surface area of minerals (quartz, biotite, and mixed opaque kaolinite/goethite) emitted fluorescence from cell-impermeant propidium iodide than from cell-permeant SYTO 9, which suggested greater coverage of minerals by extracellular DNA or DNA in non-intact cells than by intact cells. Microscopic observations of predominantly non-intact cell material in deep saprolite were consistent with the abundance of rRNA sequences related to heterotrophic bacteria in clone libraries prepared from community DNA. A few sequences were affiliated with bacteria recognized to produce siderophores, oxidize Fe(II), or fix N₂. Bacterial DNA in deep regolith from two boreholes 1.5 m apart yielded libraries with high diversity and taxa specific for each borehole. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.     

Mechanisms of iron and haem transport by Listeria monocytogenes

Abstract

Listeria monocytogenes, the causative agent of listeriosis, is a virulent foodborne Gram-positive bacterial pathogen, with 20–30% mortality. It has a broad ability to transport iron, either in the form of ferric siderophores, or by extracting it from mammalian iron binding proteins. In this review we focus on the mechanisms of ferric siderophore and haem transport into the listerial cell. Despite the fact that it does not synthesize siderophores, L. monocytogenes transports ferric siderophores in the wild environment by the actions of cytoplasmic membrane ABC-transporter systems. The bacterium acquires haem, on the other hand, by two mechanisms. At low (nanomolar) concentrations, sortase B-dependent, peptidoglycan-anchored proteins scavenge the iron porphyrin in human or animal tissues, and transfer it to the underlying ABC-transporters in the cytoplasmic membrane for uptake. At concentrations at or above 50 nM, however, haem transport becomes sortase-independent, and occurs by direct interactions of the iron porphyrin with the same ABC-transporter complexes. The architecture of the Gram-positive cell envelope plays a fundamental role in these mechanisms, and the haem acquisition abilities of L. monocytogenes are an element of its ability to cause infectious disease.     

Transient Iron-Overload with Bleomycin-Detectable Iron Present During Cardiopulmonary Bypass Surgery

Extracorporeal circulation of blood during cardiopulmonary bypass surgery exposes cells to non-physiological surfaces and shear stress which can activate several regulatory cascades, and neutrophils to release superoxide and hydrogen peroxide. Shear stresses generated by pumps and suction systems cause lysis of red blood cells and the release of haemoglobin. Together the release of reactive forms of oxygen and haemoglobin can lead to the appearance of low molecular mass chelatable iron (bleomycin-detectable iron). All patients undergoing open heart surgery appear to release iron to plasma transferrin, increasing its iron saturation. In 13% of patients, however, the transferrin became fully iron-saturated, and by the end of open-heart surgery we could detect bleomycin-chelatable iron in the plasma. Saturation of transferrin with iron eliminates its iron-binding antioxidant properties, which can result in a stimulation of iron-dependent radical damage to selected detector molecules.