Biochemical evolution III: polymerization on organophilic silica-rich surfaces, crystal-chemical modeling, formation of first cells, and geological clues.
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Catalysis at organophilic silica-rich surfaces of zeolites and feldspars might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and other geological sources. Crystal-chemical modeling yielded packings for amino acids neatly encapsulated in 10-ring channels of the molecular sieve silicalite-ZSM-5-(mutinaite). Calculation of binding and activation energies for catalytic assembly into polymers is progressing for a chemical composition with one catalytic Al-OH site per 25 neutral Si tetrahedral sites. Internal channel intersections and external terminations provide special stereochemical features suitable for complex organic species. Polymer migration along nano/micrometer channels of ancient weathered feldspars, plus exploitation of phosphorus and various transition metals in entrapped apatite and other microminerals, might have generated complexes of replicating catalytic biomolecules, leading to primitive cellular organisms. The first cell wall might have been an internal mineral surface, from which the cell developed a protective biological cap emerging into a nutrient-rich "soup." Ultimately, the biological cap might have expanded into a complete cell wall, allowing mobility and colonization of energy-rich challenging environments. Electron microscopy of honeycomb channels inside weathered feldspars of the Shap granite (northwest England) has revealed modern bacteria, perhaps indicative of Archean ones. All known early rocks were metamorphosed too highly during geologic time to permit simple survival of large-pore zeolites, honeycombed feldspar, and encapsulated species. Possible microscopic clues to the proposed mineral adsorbents/catalysts are discussed for planning of systematic study of black cherts from weakly metamorphosed Archaean sediments. (+info)
A role for the mannose-sensitive hemagglutinin in biofilm formation by Vibrio cholerae El Tor.
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While much has been learned regarding the genetic basis of host-pathogen interactions, less is known about the molecular basis of a pathogen's survival in the environment. Biofilm formation on abiotic surfaces represents a survival strategy utilized by many microbes. Here it is shown that Vibrio cholerae El Tor does not use the virulence-associated toxin-coregulated pilus to form biofilms on borosilicate but rather uses the mannose-sensitive hemagglutinin (MSHA) pilus, which plays no role in pathogenicity. In contrast, attachment of V. cholerae to chitin is shown to be independent of the MSHA pilus, suggesting divergent pathways for biofilm formation on nutritive and nonnutritive abiotic surfaces. (+info)
Origin of graphitic carbon and pentlandite in matrix olivines in the Allende meteorite.
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Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials. (+info)
Stable five- and six-coordinated silicate anions in aqueous solution.
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Addition of aliphatic polyols to aqueous silicate solutions is shown to yield high concentrations of stable polyolate complexes containing five- or six-coordinated silicon. Coordinating polyols require at least four hydroxy groups, two of which must be in threo configuration, and coordinate to silicon via hydroxy oxygens at chain positions on either side of the threo pair. The remarkable ease by which these simple sugar-like molecules react to form hypervalent silicon complexes in aqueous solution supports a long-standing supposition that such species play a significant role in the biological uptake and transport of silicon and in mineral diagenesis. (+info)
An infrared spectral match between GEMS and interstellar grains.
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Infrared spectral properties of silicate grains in interplanetary dust particles (IDPs) were compared with those of astronomical silicates. The approximately 10-micrometer silicon-oxygen stretch bands of IDPs containing enstatite (MgSiO3), forsterite (Mg2SiO4), and glass with embedded metal and sulfides (GEMS) exhibit fine structure and bandwidths similar to those of solar system comets and some pre-main sequence Herbig Ae/Be stars. Some GEMS exhibit a broad, featureless silicon-oxygen stretch band similar to those observed in interstellar molecular clouds and young stellar objects. These GEMS provide a spectral match to astronomical "amorphous" silicates, one of the fundamental building blocks from which the solar system is presumed to have formed. (+info)
Windows through the dusty disks surrounding the youngest low-mass protostellar objects.
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The formation and evolution of young low-mass stars are characterized by important processes of mass loss and accretion occurring in the innermost regions of their placentary circumstellar disks. Because of the large obscuration of these disks at optical and infrared wavelengths in the early protostellar stages (class 0 sources), they were previously detected only at radio wavelengths using interferometric techniques. We have detected with the Infrared Space Observatory the mid-infrared (mid-IR) emission associated with the class 0 protostar VLA1 in the HH1-HH2 region located in the Orion nebula. The emission arises in three wavelength windows (at 5. 3, 6.6, and 7.5 micrometers) where the absorption due to ices and silicates has a local minimum that exposes the central part of the young protostellar system to mid-IR investigations. The mid-IR emission arises from a central source with a diameter of 4 astronomical units at an averaged temperature of approximately 700 K, deeply embedded in a dense region with a visual extinction of 80 to 100 magnitudes. (+info)
Age of Neoproterozoic bilatarian body and trace fossils, White Sea, Russia: implications for metazoan evolution.
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A uranium-lead zircon age for a volcanic ash interstratified with fossil-bearing, shallow marine siliciclastic rocks in the Zimnie Gory section of the White Sea region indicates that a diverse assemblage of body and trace fossils occurred before 555.3 +/- 0.3 million years ago. This age is a minimum for the oldest well-documented triploblastic bilaterian Kimberella. It also makes co-occurring trace fossils the oldest that are reliably dated. This determination of age implies that there is no simple relation between Ediacaran diversity and the carbon isotopic composition of Neoproterozoic seawater. (+info)
Porous apatite-wollastonite glass-ceramic as an intramedullary plug.
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We evaluated the efficacy and biocompatibility of porous apatite-wollastonite glass ceramic (AW-GC) as an intramedullary plug in total hip replacement (THR) for up to two years in 22 adult beagle dogs. Cylindrical porous AW-GC rods (70% porosity, mean pore size 200 microm) were prepared. Four dogs were killed at 1, 3, 6 and 12 months each and six at 24 months after implantation. Radiological evaluation confirmed the efficacy of porous AW-CG as an intramedullary plug. Histological evaluation showed osteoconduction at one month and resorption of the porous AW-GC, which was replaced by newly-formed bone, at 24 months. Our findings indicate that porous AW-GC can be used clinically as an intramedullary plug in THR. (+info)