Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite

Bioreduction of As­(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in groundwaters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe­(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe­(II)-induced transformation of As­(III)- and As­(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As­(III) and As­(V) slowed the transformation, with the effect being greater for As­(III) than for As­(V). Prior to the formation of magnetite, As­(III) adsorbed on both lepidocrocite and green rust, whereas As­(V) associated exclusively with green rust, When magnetite precipitated, As­(III) formed surface complexes on magnetite nanoparticles and As­(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As­(V) removal from solution was higher than As­(III) removal following magnetite formation, which suggests that conversion of As­(III) to As­(V) is preferred when using As-magnetite precipitation to treat As-contaminated groundwaters

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-0

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>main zinc finger; C2HC, zinc finger; MYST HAT, conserved HAT domain characteristic of MYST family members; Acidic, glutamate/aspartate-rich region; SM-rich, serine/methionine-rich domain. MYST4 is composed of 2054 residues in which the N-terminal region and the SM-rich domain encode transcriptional repression and activation domains respectively. B) Schematic illustration of MYST4 showing the alternative MYST4 splicing variants MORF and MORFα. Conserved regions between either 2 or 3 sequences are highlighted in gray and black respectively. Regions used for primer designs are underlined in blue (forward) and in red (reverse). The number of residues in each sequence is indicated on the right. (Accession numbers: MYST4; [GenBank; ], MORF; [GenBank; ], MORFα; [GenBank; ]

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-2

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>with an anti-bovine MYST4. From left to right, Br, brain; Th, thymus; Mu, muscle; Lu, Lung; He, heart; Li, liver; Ki, kidney; Sp, spleen; Te, testicle; Ov, ovary; Ut, uterus; Oo, germinal vesicle stage oocytes. TUBULIN and β-ACTIN antibodies were incubated simultaneously on the same membrane and were used as control

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-6

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>s and round spermatids (C, D, E), round spermatids and elongating spermatids (F, G, H), round spermatids and elongated spermatids (I, J, K). Images D, G, K are enlargements of boxed sections in C, F, I respectively. In magnified sections, arrowheads indicate: round spermatocyte (D), nucleus (left) and tail (up) of an elongating spermatid (G) and nuclei of elongated spermatids located in inner (up) wall and inside (left) of the lumen (J). Positive sections were incubated with anti-MYST4 (A, C, D, F, G, I, J) and negatives were prepared by peptide-blocking assay (B, E, H, K). Original magnification 1000× (A, B)

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-3

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>oocyte nuclei (C, D); portion of large antral follicles, arrowheads indicating granulosa cells (right), theca (down) and basal lamina (left) (E, F) and blood vessels (G, H). Positive sections were incubated with anti-MYST4 (A, C, E, G,) and negatives were prepared by peptide-blocking assay (B, D, F, H). Original magnifications: 200× (C, D, E, F, G, H) and 400× (A, B)

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-4

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p> relative mRNA levels shown represent the quantity of transcript corrected for the value obtained for each pool. The highest level was attributed the relative value of 100. Shown is the relative mRNA abundance (mean ± SEM). Different letters indicate a significant difference of relative mRNA abundance (P < 0.05)

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-7

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>main zinc finger; C2HC, zinc finger; MYST HAT, conserved HAT domain characteristic of MYST family members; Acidic, glutamate/aspartate-rich region; SM-rich, serine/methionine-rich domain. MYST4 is composed of 2054 residues in which the N-terminal region and the SM-rich domain encode transcriptional repression and activation domains respectively. B) Schematic illustration of MYST4 showing the alternative MYST4 splicing variants MORF and MORFα. Conserved regions between either 2 or 3 sequences are highlighted in gray and black respectively. Regions used for primer designs are underlined in blue (forward) and in red (reverse). The number of residues in each sequence is indicated on the right. (Accession numbers: MYST4; [GenBank; ], MORF; [GenBank; ], MORFα; [GenBank; ]

Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis-5

<p><b>Copyright information:</b></p><p>Taken from "Investigation of MYST4 histone acetyltransferase and its involvement in mammalian gametogenesis"</p><p>http://www.biomedcentral.com/1471-213X/7/123</p><p>BMC Developmental Biology 2007;7():123-123.</p><p>Published online 2 Nov 2007</p><p>PMCID:PMC2190771.</p><p></p>ly blastocyst and blastocyst) stained with an anti-MYST4 antibody (green signal) and with propidium iodide (red signal) to visualize the DNA. Original magnification 600×

Electronic Supporting Material from Elongated magnetite nanoparticle formation from a solid ferrous precursor in a magnetotactic bacterium

Magnetotactic bacteria are aquatic microorganisms that intracellularly mineralize ferrimagnetic nanoparticles enabling the cells to align with the geomagnetic field. The bacteria produce a magnetic mineral of species-specific phase (magnetite Fe(II)Fe(III)₂O₄ or greigite Fe(II)Fe(III)₂S₄), size, morphology and particle assembly. Several species produce crystals of unusual elongated particle shapes, which break the symmetry of the thermodynamically favoured isometric morphology. Such morphologies are thought to affect domain size and orientation of the internal magnetization. Therefore, they are interesting study objects to develop new synthetic strategies for the morphological control of nanoparticles. We investigate the formation of such irregularly shaped nanomagnets in the species <i>Desulfovibrio magneticus</i> RS-1. In contrast to previously described organisms, this bacterium accumulates iron predominantly as Fe(II) rather than Fe(III) consistent with an alternative oxidative biomineralization route. Further, using high-resolution electron microscopy, we observe an epitaxial relationship between precursor and the final mineral phase supporting the notion of a solid-state transformation pathway. The precursor is likely a green rust previously thought to convert to magnetite only by dissolution and re-precipitation. Our findings represent a novel observation in the interconversion of iron (oxyhydr)oxide materials and suggest that solid-state growth processes could be required to produce irregularly shaped, elongated magnetite nanocrystals

Green Rust Formation during Fe(II) Oxidation by the Nitrate-Reducing <i>Acidovorax</i> sp. Strain BoFeN1

Green rust (GR) as highly reactive iron mineral potentially plays a key role for the fate of (in)­organic contaminants, such as chromium or arsenic, and nitroaromatic compounds functioning both as sorbent and reductant. GR forms as corrosion product of steel but is also naturally present in hydromorphic soils and sediments forming as metastable intermediate during microbial Fe­(III) reduction. Although already suggested to form during microbial Fe­(II) oxidation, clear evidence for GR formation during microbial Fe­(II) oxidation was lacking. In the present study, powder XRD, synchrotron-based XAS, Mössbauer spectroscopy, and TEM demonstrated unambiguously the formation of GR as an intermediate product during Fe­(II) oxidation by the nitrate-reducing Fe­(II)-oxidizer <i>Acidovorax</i> sp. strain BoFeN1. The spatial distribution and Fe redox-state of the precipitates associated with the cells were visualized by STXM. It showed the presence of extracellular Fe­(III), which can be explained by Fe­(III) export from the cells or extracellular Fe­(II) oxidation by an oxidant diffusing from the cells. Moreover, GR can be oxidized by nitrate/nitrite and is known as a catalyst for oxidation of dissolved Fe­(II) by nitrite/nitrate and may thus contribute to the production of extracellular Fe­(III). As a result, strain BoFeN1 may contribute to Fe­(II) oxidation and nitrate reduction both by an direct enzymatic pathway and an indirect GR-mediated process