Discovery Prospects for a Supernova Signature of Biogenic Origin

Approximately 2.8 Myr before the present our planet was subjected to the debris of a supernova explosion. The terrestrial proxy for this event was the discovery of live atoms of 60Fe in a deep-sea ferromanganese crust. The signature for this supernova event should also reside in magnetite Fe3O4 microfossils produced by magnetotactic bacteria extant at the time of the Earth-supernova interaction, provided the bacteria preferentially uptake iron from fine-grained iron oxides and ferric hydroxides. Using estimates for the terrestrial supernova 60Fe flux, combined with our empirically derived microfossil concentrations in a deep-sea drill core, we deduce a conservative estimate of the ^{60}{Fe} fraction as 60Fe/Fe ~ 3.6 x 10^{-15}. This value sits comfortably within the sensitivity limit of present accelerator mass spectrometry capabilities. The implication is that a biogenic signature of this cosmic event is detectable in the Earth's fossil record.Comment: As it appears in Icaru

Species richness, abundance and phenology of fungal fruit bodies over 21 years in a Swiss forest plot

Fungal fruit bodies were surveyed on a plot area of 1500 m2 from 1975¿99 (excluding 1980¿83) in the fungal reserve La Chaneaz in western Switzerland. Fruit bodies were identified and counted on a weekly basis. Species richness and abundances varied strongly between years. More than 400 species were encountered. Many species were transient; particularly rich years showed species occurring for only one year. This indicates that the number of species will substantially increase if the survey is continued. Within years, the species richness, abundances and periods of fruiting were tightly correlated. The abundance data of species within a year seemed symmetrically distributed over their fruiting period. The relation between species richness and abundances within years was studied by fitting species-abundance plots, known from numerical ecology. The surface area under the curves was taken as a parameter for ecological/fungal diversity. Productivity was correlated with the precipitation from June until October. The time of fruit body appearance was correlated with the temperatures in July and August. As groups, mycorrhizal and saprotrophic species behaved similarly over the years. The productivity of species was compared with their distribution in The Netherlands indicating a correlation between the level of local abundance and the geographic range of specie

Syntheses of 4′-thioribonucleosides and thermodynamic stability and crystal structure of RNA oligomers with incorporated 4′-thiocytosine

A facile synthetic route for the 4′-thioribonucleoside building block 4′SN (N = U, C, A and G) with the ribose O4′ replaced by sulfur is presented. Conversion of l-lyxose to 1,5-di-O-acetyl-2,3-di-O-benzoyl-4-thio-d-ribofuranose was achieved via an efficient four-step synthesis with high yield. Conversion of the thiosugar into the four ribonucleoside phosphoramidite building blocks was accomplished with additional four steps in each case. Incorporation of 4′-thiocytidines into oligoribonucleotides improved the thermal stability of the corresponding duplexes by ∼1°C per modification, irrespective of whether the strand contained a single modification or a consecutive stretch of 4′SC residues. The gain in thermodynamic stability is comparable to that observed with oligoribonucleotides containing 2′-O-methylated residues. To establish potential conformational changes in RNA as a result of the 4′-thio modification and to better understand the origins of the observed stability changes, the crystal structure of the oligonucleotide 5′-r(CC4′SCCGGGG) was determined and analyzed using the previously solved structure of the native RNA octamer as a reference. The two 4′-thioriboses adopt conformations that are very similar to the C3′-endo pucker observed for the corresponding sugars in the native duplex. Subtle changes in the local geometry of the modified duplex are mostly due to the larger radius of sulfur compared to oxygen or appear to be lattice-induced. The significantly increased RNA affinity of 4′-thio-modified RNA relative to RNA, and the relatively minor conformational changes caused by the modification render this nucleic acid analog an interesting candidate for in vitro and in vivo applications, including use in RNA interference (RNAi), antisense, ribozyme, decoy and aptamer technologie

Syntheses of 4′-thioribonucleosides and thermodynamic stability and crystal structure of RNA oligomers with incorporated 4′-thiocytosine

A facile synthetic route for the 4′-thioribonucleoside building block (4′S)N (N = U, C, A and G) with the ribose O4′ replaced by sulfur is presented. Conversion of l-lyxose to 1,5-di-O-acetyl-2,3-di-O-benzoyl-4-thio-d-ribofuranose was achieved via an efficient four-step synthesis with high yield. Conversion of the thiosugar into the four ribonucleoside phosphoramidite building blocks was accomplished with additional four steps in each case. Incorporation of 4′-thiocytidines into oligoribonucleotides improved the thermal stability of the corresponding duplexes by ∼1°C per modification, irrespective of whether the strand contained a single modification or a consecutive stretch of (4′S)C residues. The gain in thermodynamic stability is comparable to that observed with oligoribonucleotides containing 2′-O-methylated residues. To establish potential conformational changes in RNA as a result of the 4′-thio modification and to better understand the origins of the observed stability changes, the crystal structure of the oligonucleotide 5′-r(CC(4′S)CCGGGG) was determined and analyzed using the previously solved structure of the native RNA octamer as a reference. The two 4′-thioriboses adopt conformations that are very similar to the C3′-endo pucker observed for the corresponding sugars in the native duplex. Subtle changes in the local geometry of the modified duplex are mostly due to the larger radius of sulfur compared to oxygen or appear to be lattice-induced. The significantly increased RNA affinity of 4′-thio-modified RNA relative to RNA, and the relatively minor conformational changes caused by the modification render this nucleic acid analog an interesting candidate for in vitro and in vivo applications, including use in RNA interference (RNAi), antisense, ribozyme, decoy and aptamer technologies

Dendritic Zinc Growth on the Edges of Flat Steel Strip During Electro Galvanizing

AbstractDendritic growth on strip edges during continuous zinc electroplating of flat steel strip for the automotive industry is a well-known problem. They produce surface defects during the stamping process. In this work the effect of the electrolytic process variables on dendrites formation is studied. Zinc was electrodeposited on rotating steel discs. This new experimental configuration reproduces the hydrodynamic conditions and the current distribution found on the strip edge in an industrial zinc electroplating line. The tangential velocity of the outer edge of the discs was adjusted toa value equal to the relative speed between strip and fluid used in the industry. The effect of current density, temperature and edge roughness was evaluated. All these variables have a great influence on the size and morphology of dendrites

Effect of Heavy Metal Contaminated Shooting Range Soils on Mycorrhizal Colonization of Roots and Metal Uptake by Leek

We grew leek (Allium porrum) in soils of two shooting ranges heavily contaminated with heavy metals in the towns of Zuchwil and Oberuzwil in Switzerland as a bioassay to test theactivity of arbuscular mycorrhizal (AM) fungi in these soils.Soil samples were taken from (1) front of the shooting house(HOUSE), (2) the area between house and target (FIELD) and (3) the berm (BACKSTOP). Samples of Ribwort plantain (Plantagolanceolata) growing naturally within the shooting ranges werealso collected and the colonization of its roots by mycorrhizalfungi was measured. The number of AM spores in the soils wassignificantly reduced concomitant with the increase in thedegree of soil contamination with metals. In Zuchwil,mycorrhizal fungi equally colonized roots of Ribwort plantainsampled from BACKSTOP and HOUSE. In Oberuzwil, however, plantsfrom BACKSTOP had lower colonization when compared with thosesampled from HOUSE. Colonization of leek was strongly reducedin the BACKSTOP soil of Zuchwil and slightly reduced in theBACKSTOP soil of Oberuzwil when compared with plants grown inrespective HOUSE soil. Concentrations of Cd, Cr, Cu, Ni, Pb andZn in the leaves of leek grown in the BACKSTOP soil was withinthe range considered toxic for human consumption. This pointsto the high degree of bio-availability of these metal in thesesoils. Significant decrease in the number of mycorrhizal sporesin the BACKSTOP soils in Zuchwil and the low colonization ofleek roots grown in these soils point to possible changes inthe species diversity of mycorrhizal fungi in these soil