Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation

Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospirillum sp. AMB-1 as a model system, we show that magnetosome vesicles exist in the absence of magnetite, biomineralization of magnetite proceeds simultaneously in multiple vesicles, and biomineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation of functional magnetosome vesicles and displays a dynamic subcellular localization throughout the growth cycle of magnetotactic bacteria. Together, these results suggest that the magnetosome precisely coordinates magnetite biomineralization and can serve as a model system for the study of organelle biogenesis in noneukaryotic cells

Magnetofossil Spike During the Paleocene-Eocene Thermal Maximum: Ferromagnetic Resonance, Rock Magnetic, and Electron Microscopy Evidence from Ancora, New Jersey, USA

Previous workers identified a magnetically anomalous clay layer deposited on the northern United States Atlantic Coastal Plain during the Paleocene-Eocene Thermal Maximum (PETM). The finding inspired the highly controversial hypothesis that a cometary impact triggered the PETM. Here we present ferromagnetic resonance (FMR), isothermal and anhysteretic remanent magnetization, first order reversal curve, and transmission electron microscopy analyses of late Paleocene and early Eocene sediments in drillcore from Ancora, New Jersey. A novel paleogeographic analysis applying a recent paleomagnetic pole from the Faeroe Islands indicates that New Jersey during the initial Eocene had a ~6-9 degrees lower paleolatitude (~27.3 degrees for Ancora) and a more zonal shoreline trace than in conventional reconstructions. Our investigations of the PETM clay from Ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria. This result, the first identification of ancient biogenic magnetite using FMR, argues that the anomalous magnetic properties of the PETM sediments are not produced by an impact. They instead reflect environmental changes along the eastern margin of North America during the PETM that led to enhanced production and/or preservation of magnetofossils

Trace elements can influence the physical properties of tooth enamel

In previous studies, we showed that the size of apatite nanocrystals in tooth enamel can influence its physical properties. This important discovery raised a new question; which factors are regulating the size of these nanocrystals? Trace elements can affect crystallographic properties of synthetic apatite, therefore this study was designed to investigate how trace elements influence enamel’s crystallographic properties and ultimately its physical properties. The concentration of trace elements in tooth enamel was determined for 38 extracted human teeth using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The following trace elements were detected: Al, K, Mg, S, Na, Zn, Si, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and Ti. Simple and stepwise multiple regression was used to identify the correlations between trace elements concentration in enamel and its crystallographic structure, hardness, resistance to crack propagation, shade lightness and carbonate content. The presence of some trace elements in enamel was correlated with the size (Pb, Ti, Mn) and lattice parameters (Se, Cr, Ni) of apatite nanocrystals. Some trace elements such as Ti was significantly correlated with tooth crystallographic structure and consequently with hardness and shade lightness. We conclude that the presence of trace elements in enamel could influence its physical properties. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/2193-1801-2-499) contains supplementary material, which is available to authorized users

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria

Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 - 75 degree(s)C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh (-200 mV to -415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl2 caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001

Untangling the Roles of Anti-Apoptosis in Regulating Programmed Cell Death using Humanized Yeast Cells

Genetically programmed cell death (PCD) mechanisms, including apoptosis, are important for the survival of metazoans since it allows, among things, the removal of damaged cells that interfere with normal function. Cell death due to PCD is observed in normal processes such as aging and in a number of pathophysiologies including hypoxia (common causes of heart attacks and strokes) and subsequent tissue reperfusion. Conversely, the loss of normal apoptotic responses is associated with the development of tumors. So far, limited success in preventing unwanted PCD has been reported with current therapeutic approaches despite the fact that inhibitors of key apoptotic inducers such as caspases have been developed. Alternative approaches have focused on mimicking anti-apoptotic processes observed in cells displaying increased resistance to apoptotic stimuli. Hormesis and pre-conditioning are commonly observed cellular strategies where sub-lethal levels of pro-apoptotic stimuli lead to increased resistance to higher or lethal levels of stress. Increased expression of anti-apoptotic sequences is a common mechanism mediating these protective effects. The relevance of the latter observation is exemplified by the observation that transgenic mice overexpressing anti-apoptotic genes show significant reductions in tissue damage following ischemia. Thus strategies aimed at increasing the levels of anti-apoptotic proteins, using gene therapy or cell penetrating recombinant proteins are being evaluated as novel therapeutics to decrease cell death following acute periods of cell death inducing stress. In spite of its functional and therapeutic importance, more is known regarding the processes involved in apoptosis than anti-apoptosis. The genetically tractable yeast Saccharomyces cerevisiae has emerged as an exceptional model to study multiple aspects of PCD including the mitochondrial mediated apoptosis observed in metazoans. To increase our knowledge of the process of anti-apoptosis, we screened a human heart cDNA expression library in yeast cells undergoing PCD due to the conditional expression of a mammalian pro-apoptotic Bax cDNA. Analysis of the multiple Bax suppressors identified revealed several previously known as well as a large number of clones representing potential novel anti-apoptotic sequences. The focus of this review is to report on recent achievements in the use of humanized yeast in genetic screens to identify novel stress-induced PCD suppressors, supporting the use of yeast as a unicellular model organism to elucidate anti-apoptotic and cell survival mechanisms

A Genetic Strategy for Probing the Functional Diversity of Magnetosome Formation

Model genetic systems are invaluable, but limit us to understanding only a few organisms in detail, missing the variations in biological processes that are performed by related organisms. One such diverse process is the formation of magnetosome organelles by magnetotactic bacteria. Studies of model magnetotactic α-proteobacteria have demonstrated that magnetosomes are cubo-octahedral magnetite crystals that are synthesized within pre-existing membrane compartments derived from the inner membrane and orchestrated by a specific set of genes encoded within a genomic island. However, this model cannot explain all magnetosome formation, which is phenotypically and genetically diverse. For example, Desulfovibrio magneticus RS-1, a δ-proteobacterium for which we lack genetic tools, produces tooth-shaped magnetite crystals that may or may not be encased by a membrane with a magnetosome gene island that diverges significantly from those of the α-proteobacteria. To probe the functional diversity of magnetosome formation, we used modern sequencing technology to identify hits in RS-1 mutated with UV or chemical mutagens. We isolated and characterized mutant alleles of 10 magnetosome genes in RS-1, 7 of which are not found in the α-proteobacterial models. These findings have implications for our understanding of magnetosome formation in general and demonstrate the feasibility of applying a modern genetic approach to an organism for which classic genetic tools are not available

Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum

We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, New Jersey. Aside from previously-described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability – a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming – drove diversification of magnetite-forming organisms, likely including eukaryotes

Peroxisome division in the yeast Yarrowia lipolytica is regulated by a signal from inside the peroxisome

We describe an unusual mechanism for organelle division. In the yeast Yarrowia lipolytica, only mature peroxisomes contain the complete set of matrix proteins. These mature peroxisomes assemble from several immature peroxisomal vesicles in a multistep pathway. The stepwise import of distinct subsets of matrix proteins into different immature intermediates along the pathway causes the redistribution of a peroxisomal protein, acyl-CoA oxidase (Aox), from the matrix to the membrane. A significant redistribution of Aox occurs only in mature peroxisomes. Inside mature peroxisomes, the membrane-bound pool of Aox interacts with Pex16p, a membrane-associated protein that negatively regulates the division of early intermediates in the pathway. This interaction inhibits the negative action of Pex16p, thereby allowing mature peroxisomes to divide

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria

Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 - 75 degree(s)C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh (-200 mV to -415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl2 caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001

Biological Oxidant and Life Detection (BOLD) mission: an outline for a new mission to Mars

The Viking mission was the only mission to date that conducted life detection experiments. It revealed ambiguous and still controversial results. New findings and hypotheses urge a re-evaluation of the Viking results and a re-evaluation of the evidence for the possible presence of life on Mars in general. Recent findings of abundant water ice on Mars, the presence of liquid contemporary water on the Martian surface, and the detection of methane in the Martian atmosphere further support this possibility. Current missions to be launched focus on habitability considerations (e.g., NASA Phoenix, NASA Mars Science Laboratory), but shy away from directly testing for life on Mars, with the potential exception of the ESA ExoMars mission. If these currently planned missions collect positive evidence toward habitability and the possible existence of extraterrestrial (microbial) life on Mars, it would be timely to propose a new mission to Mars with a strong life detection component. We propose such a mission called BOLD: Biological Oxidant and Life Detection Mission. The BOLD mission objective would be to quantify the amount of hydrogen peroxide existing in the Martian soil and to test for processes typically associated with life. Six landing packages are projected to land on Mars that include a limited power supply, a set of oxidant and life detection experiments, and a transmitter, which is able to transmit information via an existing Mars orbiter back to Earth