2,247 research outputs found
Bibliography on inactivation of viruses and rickettsiae by heat
Inactivation of viruses and rickettsiae by heat - bibliograph
A comment on “Metamorphic origin of anastomosing and wavy laminas overprinting putative microbial deposits from the 3.22 Ga Moodies Group (Barberton Greenstone Belt)”
Lagrangian statistics in forced two-dimensional turbulence
We report on simulations of two-dimensional turbulence in the inverse energy
cascade regime. Focusing on the statistics of Lagrangian tracer particles,
scaling behavior of the probability density functions of velocity fluctuations
is investigated. The results are compared to the three-dimensional case. In
particular an analysis in terms of compensated cumulants reveals the transition
from a strong non-Gaussian behavior with large tails to Gaussianity. The
reported computation of correlation functions for the acceleration components
sheds light on the underlying dynamics of the tracer particles.Comment: 8 figures, 1 tabl
Tuning excitability by alloying: the Rh(111)/Ni/H2 + O2 system
The dynamic behavior of the O2 + H2 reaction on a Rh(111) surface alloyed with Ni has been studied in the 10(-5) mbar range using photoemission electron microscopy (PEEM) as a spatial resolving method. For T = 773 K and p(O2) = 5 x 10(-5) mbar the bifurcation diagram has been mapped out as a function of the Ni coverage in a range of 0 ML /= 1.3 ML. A critical Ni coverage of Theta(Ni,crit) = 0.13 monolayers (ML) is required for excitability. In the excitable parameter range pulse trains and irregular chemical wave patterns are found. Whereas the propagation speed of the pulses exhibits no clear-cut dependence on the Ni coverage, the frequency of the local PEEM intensity oscillations increases linearly with Ni coverage in the range from Theta(Ni) = 0.13 ML to Theta(Ni) = 1.3 ML.DF
BACCHUS-3D/SP A computer programme for the three-dimensional description of sodium single-phase flow in bundle geometry
Morphological adaptations of 3.22 Ga-old tufted microbial mats to Archean coastal habitats (Moodies Group, Barberton Greenstone Belt, South Africa)
Microbial life was well established and widespread by the Paleoarchean; however, the degree of evolutionary advancement such as microbial motility, intra- and inter-species interactions, phototropism, or oxygenic photosynthesis by that time remains highly debated. The 3.22 Ga Moodies Group in the Barberton Greenstone Belt (BGB, South Africa) are Earth's oldest well-preserved siliciclastic tidal deposits. They exhibit a unique assemblage of microbial mats, providing an excellent opportunity to decipher the morphological adaptations of microbial communities to different paleoenvironmental settings. The fossil mats are preserved as kerogenous laminations (0.5–1 mm thick) that can be traced laterally for ∼15 km in a ∼1000 m-thick succession of fine- to coarse-grained tidal sandstones and conglomerates. We here present a detailed stratigraphic and depositional facies analysis, documenting the association of the three principal mat morphotypes with specific environmental settings: (1) planar-type in coastal floodplain, (2) wavy-type in intertidal, and (3) tufted-type in upper inter- to supratidal facies. All mat types indicate a flourishing phototrophic biota; moreover, the tufted morphology suggests an intricate level of coordinated growth commonly known from cyanobacterial mats in modern environments
Earth's first snowball event: Evidence from the early Paleoproterozoic Huronian Supergroup
Ever since it was first proposed that the Earth completely froze during glaciations ∼ 640 million years ago evidence supporting this hypothesis has been increasing, primarily from samples of carbonates directly overlying glacial diamictites, termed cap carbonates. However, this was not the first extensive glacial period that affected planet Earth: ∼1750 million years prior to Neoproterozoic glaciations the Earth went through its first major glacial episode, the early Paleoproterozoic Huronian glaciations. The second Huronian ice advance deposited the Bruce Formation, with its overlying cap carbonate, the Espanola Formation. This up to ∼ 300 m thick succession of limestone, siltstone, dolostone and sandstone overlies diamictite containing a dropstone-bearing layer with δ13Ccarb of −10‰. The 12C-enriched interval also has rare earth element (REE) patterns with negative Eu anomalies, radiogenic Sr isotopes, and negative εNd(0) in the carbonate. The first of these observations is probably due to highly reducing conditions in the sediment, and the possible thawing of methane-rich areas, releasing fluids that mixed with the overlying bottom waters; the last two reflect the diagenetic incorporation into the carbonate of radiogenic Sr, and derivation of REEs, including Nd, from abundant silty loess. This infers a stratified water mass with a relatively stagnant bottom layer during disintegration of an ice shelf. Above this REE patterns through the basal Espanola become increasingly more light depleted upwards, C becomes heavier, Sr is less radiogenic, εNd(0) is near 0 and one area has up to ∼ 1300 ppm Ba incorporated into the carbonate, indicating breakdown of water-mass stratification. Vertically over ∼ 200 m δ13Ccarb increases from −4.5 to −2.5‰ as the environment shallowed incorporating gradually increasing amounts of seawater into the freshwater plume, which initially extended to depths below wave base. Strata deposited in the upper Espanola near the strandline contain layers of Fe-Mn-rich dolomite with positive Eu anomalies reflecting Paleoproterozioc seawater composition dominating even the nearshore by this time. These observations are similar to those from Neoproterozoic cap carbonates, and provide new evidence for the possibly snowball Earth-like nature of the ∼ 2.4 Ga Bruce glaciation
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Harnessing Natural Diversity to Probe Metabolic Pathways
Analyses of cellular processes in the yeast Saccharomyces cerevisiae rely primarily upon a small number of highly domesticated laboratory strains, leaving the extensive natural genetic diversity of the model organism largely unexplored and unexploited. We asked if this diversity could be used to enrich our understanding of basic biological processes. As a test case, we examined a simple trait: the utilization of di/tripeptides as nitrogen sources. The capacity to import small peptides is likely to be under opposing selective pressures (nutrient utilization versus toxin vulnerability) and may therefore be sculpted by diverse pathways and strategies. Hitherto, dipeptide utilization in S. cerevisiae was solely ascribed to the activity of a single protein, the Ptr2p transporter. Using high-throughput phenotyping and several genetically diverse strains, we identified previously unknown cellular activities that contribute to this trait. We find that the Dal5p allantoate/ureidosuccinate permease is also capable of facilitating di/tripeptide transport. Moreover, even in the absence of Dal5p and Ptr2p, an additional activity—almost certainly the periplasmic asparaginase II Asp3p—facilitates the utilization of dipeptides with C-terminal asparagine residues by a different strategy. Another, as-yet-unidentified activity enables the utilization of dipeptides with C-terminal arginine residues. The relative contributions of these activities to the utilization of di/tripeptides vary among the strains analyzed, as does the vulnerability of these strains to a toxic dipeptide. Only by sampling the genetic diversity of multiple strains were we able to uncover several previously unrecognized layers of complexity in this metabolic pathway. High-throughput phenotyping facilitates the rapid exploration of the molecular basis of biological complexity, allowing for future detailed investigation of the selective pressures that drive microbial evolution.</p
Evidence for cavity-dwelling microbial life in 3.22 Ga tidal deposits
Cavities are considered plausible and favorable habitats for life on early Earth. In such microenvironments, organisms may have found an adequate protection against the intense ultraviolet radiation that characterized the Archean ozone-free atmosphere. However, while there is clear evidence that benthic life existed in the Paleoarchean, the oldest traces of cavity-dwelling microbes (coelobionts) have been found in Neoarchean rocks. Here we present the results of a detailed investigation of early silicified cavities occurring in the oldest well-preserved siliciclastic tidal deposits, the 3.22 Ga Moodies Group of the Barberton Greenstone Belt (South Africa). Downward-growing microstromatolitic columns composed of kerogenous laminae are commonly present in planar, bedding-parallel, now silica-filled cavities that formed in sediments of the peritidal zone. In-situ δ13CPDB (PDB—Peedee belemnite) measurements of the kerogen range from –32.3‰ to –21.3‰ and are consistent with a biogenic origin. Scanning electron microscopy analysis of the silicified cavities shows well-preserved chains of cell-sized molds that are interpreted as fossil filamentous microorganisms. The geological context, the morphology of the microstromatolites, the δ13C composition of the kerogen, and the presence of microfossils all suggest that a microbial community inhabited the cavities. These results extend the geological record of coelobionts by ∼500 m.y., supporting the view that cavities were among the first ecological niches to have been occupied by early microorganisms
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