The Sirius Passet Lagerstätte: silica death masking opens the window on the earliest matground community of the Cambrian explosion

The Sirius Passet Lagerstätte (SP), Peary Land, North Greenland, occurs in black slates deposited at or just below storm wave base. It represents the earliest Cambrian microbial mat community with exceptional preservation, predating the Burgess Shale by 10 million years. Trilobites from the SP are preserved as complete, three‐dimensional, concave hyporelief external moulds and convex epirelief casts. External moulds are shown to consist of a thin veneer of authigenic silica. The casts are formed from silicified cyanobacterial mat material. Silicification in both cases occurred shortly after death within benthic cyanobacterial mats. Pore waters were alkali, silica‐saturated, high in ferric iron but low in oxygen and sulphate. Excess silica was likely derived from remobilized biogenic silica. The remarkable siliceous death mask preservation opens a new window on the environment and location of the Cambrian Explosion. This window closed with the appearance of abundant mat grazers later as the Cambrian Explosion intensified.     

Mitochondrial DNA structure and colony expansion dynamics of New Zealand fur seals (Arctocephalus forsteri) around Banks Peninsula

New Zealand fur seals are one of many pinniped species that survived the commercial sealing of the eighteenth and nineteenth centuries in dangerously low numbers. After the enforcement of a series of protection measures in the early twentieth century, New Zealand fur seals began to recover from the brink of extinction. We examined the New Zealand fur seal populations of Banks Peninsula, South Island, New Zealand using the mitochondrial DNA control region. We identified a panmictic population structure around Banks Peninsula. The most abundant haplotype in the area showed a slight significant aggregated structure. The Horseshoe Bay colony showed the least number of shared haplotypes with other colonies, suggesting a different origin of re-colonisation of this specific colony. The effective population size of the New Zealand fur seal population at Banks Peninsula was estimated at approximately 2500 individuals. The exponential population growth rate parameter for the area was 35, which corresponds to an expanding population. In general, samples from adjacent colonies shared 4.4 haplotypes while samples collected from colonies separated by between five and eight bays shared 1.9 haplotypes. The genetic data support the spill-over dynamics of colony expansion already suggested for this species. Approximate Bayesian computations analysis suggests re-colonisation of the area from two main clades identified across New Zealand with a most likely admixture coefficient of 0.41 to form the Banks Peninsula population. Approximate Bayesian computations analysis estimated a founder population size of approximately 372 breeding individuals for the area, which then rapidly increased in size with successive waves of external recruitment. The population of fur seals in the area is probably in the late phase of maturity in the colony expansion dynamic.     

Effect of hydrocarbon concentration of pasture production (<i>Brachiaria humidicola</i>) in Texistepec,Veracruz

In this study, the relationship between the concentration of extra-heavy crude petroleum in a clayey material and the toxicity, field capacity, temperature, and growth of a tropical forage grass (Brachiara humidicola) was determined empirically. For this type of petroleum the acute toxicity (Microtox^®) was slight (CE₅₀ = 63200 - 76400 mg/kg) even at high hydrocarbon concentrations (29279 mg/kg). Nonetheless, serious impacts were encountered in terms of an increase in soil temperature (+ 1.3 °C), reduction in field capacity (-10.7%) and reduction in aerial biomass (-97%). The relationship between hydrocarbon concentration and biomass resulted in a typical dose-response curve (r = 0.99), where a concentration of 2626 mg/kg of hydrocarbons corresponds to a maintenance of 90% biomass. Furthermore, during the duration of this study (one year) the biodegradation was proportional to the pasture biomass production (r = 0.997) indicating a synergistic relationship between the petroleum biodegrading microorganisms in the rhizosphere and the pasture.     

The antimitotic effect of the neem terpenoid azadirachtin on cultured insect cells

When cultured insect cells (Sf9) were grown in the presence of 5 x 10(-6) M azadirachtin, there was a rapid increase in the mitotic index, with the appearance of many aberrant mitotic figures. Flow cytometry established that cells accumulated in the G2/M phase of the cell cycle, and that the effect was concentration-dependent. At 10(-8) M a period of 20 h was necessary to raise the proportion in G2/M to 42% above the control values, but at 5 x 10(-6) M more than 90% of the cells were in this phase. Azadirachtin had the same effect on C6/36 mosquito cells, but failed to affect L929 murine fibroblast cells even at a concentration of 10(-4) M over 72 h. Experiments with colchcine and taxol showed similarities of action between azadirachtin and colchicine, and azadirachtin was apparently able to displace colchicine-fluorescein from binding-sites in living insect cells. Another similarity between azdirachtin and colchicine was that both phytochemicals prevented the polymerisatrion in vitro of mammalian tubulin, although the azadirachtin was much less effective.     

Structures of neutral oligosaccharides isolated from the respiratory mucins of a non-secretor (O, Le(a+b-)) patient suffering from chronic bronchitis.

Mucin glycopeptides were prepared from the respiratory mucus of a non-secretor, chronic bronchitis patient with blood group O, Le(a+b-). Oligosaccharides were released by alkaline-borohydride treatment and purified by anion-exchange chromatography, size exclusion chromatography, and HPLC on a silica-bonded alkylamine column. Structural studies employed 500-MHz 1H-NMR spectroscopy, fast-atom-bombardment mass spectrometry and methylation analysis. Twenty-four neutral oligosaccharides, ranging in size from disaccharides to hexasaccharides, were fully characterized in this study. None of the structures contained an alpha(1----2)-linked fucose residue, in keeping with the non-secretor status of the patient. Seven of the structures had fucose present in alpha(1----3)-linkage in the X-determinant, while only one oligosaccharide (compound 14b) was seen with fucose alpha(1----4)-linked in the Le(a) determinant. The following eight structures isolated from the mucins of the non-secretor patient had not been found previously in the mucins of secretor individuals: [formula: see text] This study confirms that the blood group status of an individual is reflected in the carbohydrate structures of the secreted mucins. Furthermore, it clearly illustrates the need for detailed carbohydrate structural studies of mucins from different individuals before any attempt can be made to correlate observed differences in oligosaccharide profiles to disease status.