Enhanced procedural blank control for organic geochemical studies of critical sample material.

Organic contamination of sedimentary rocks can produce artefacts in studies of hydrocarbon composition, and this can have significant negative consequences for interpretations of the geobiological record. False positives - that is cases of non-syngenetic hydrocarbon biomarkers - are common in Precambrian studies, and significant challenges persist despite the intensive effort devoted to these studies. Efforts to standardize the 'burden of proof' for distinguishing between contamination and syngenetic material have to date failed to yield a simple or universal protocol, yet the need remains great, as both bitumen-lean rocks and bitumen-rich samples can be vulnerable to the accumulation of false-positive signals. In an effort to determine the best approach to quality control, we tested the capability of different blank materials to collect ambient contamination by assessing their capacity to adsorb hydrocarbons during storage in plastic bags and found that commonly used Quartz sand does not provide an adequate measure of storage- or laboratory-induced contamination. Brick blanks, having the advantage that they can parallel rock samples even during the sawing process, are characterized by similar poor adsorption properties. Primarily steered by mineralogy, organic carbon content and surface area, model-black shales can adsorb up to 20 times more contaminants than sand blanks and up to 200 times more contaminants than organic-free model-carbonates. This observation provides an explanation for reports and observations of seemingly systematic stratigraphic variation of contaminants, but mostly should raise awareness for the evaluation of procedural blanks, in particular of sample-to-blank ratios, when studying bitumen-lean rock samples of varying lithologies. Additionally, differences between the hydrocarbon profiles in plastic bags and the hydrocarbon signatures transferred to blank materials emphasize difficulties in the unequivocal detection of contamination sources. Artificial black shale pellets can provide enhanced contamination control in biomarker studies - particularly for exceptionally vulnerable samples such as Precambrian rocks, meteorites or extraterrestrial sample-return material.

Carbon and sulfur isotopic signatures of ancient life and environment at the microbial scale: Neoarchean shales and carbonates.

An approach to coordinated, spatially resolved, in situ carbon isotope analysis of organic matter and carbonate minerals, and sulfur three- and four-isotope analysis of pyrite with an unprecedented combination of spatial resolution, precision, and accuracy is described. Organic matter and pyrite from eleven rock samples of Neoarchean drill core express nearly the entire range of δ(13) C, δ(34) S, Δ(33) S, and Δ(36) S known from the geologic record, commonly in correlation with morphology, mineralogy, and elemental composition. A new analytical approach (including a set of organic calibration standards) to account for a strong correlation between H/C and instrumental bias in SIMS δ(13) C measurement of organic matter is identified. Small (2-3 µm) organic domains in carbonate matrices are analyzed with sub-permil accuracy and precision. Separate 20- to 50-µm domains of kerogen in a single ~0.5 cm(3) sample of the ~2.7 Ga Tumbiana Formation have δ(13) C = -52.3 ± 0.1‰ and -34.4 ± 0.1‰, likely preserving distinct signatures of methanotrophy and photoautotrophy. Pyrobitumen in the ~2.6 Ga Jeerinah Formation and the ~2.5 Ga Mount McRae Shale is systematically (13) C-enriched relative to co-occurring kerogen, and associations with uraniferous mineral grains suggest radiolytic alteration. A large range in sulfur isotopic compositions (including higher Δ(33) S and more extreme spatial gradients in Δ(33) S and Δ(36) S than any previously reported) are observed in correlation with morphology and associated mineralogy. Changing systematics of δ(34) S, Δ(33) S, and Δ(36) S, previously investigated at the millimeter to centimeter scale using bulk analysis, are shown to occur at the micrometer scale of individual pyrite grains. These results support the emerging view that the dampened signature of mass-independent sulfur isotope fractionation (S-MIF) associated with the Mesoarchean continued into the early Neoarchean, and that the connections between methane and sulfur metabolism affected the production and preservation of S-MIF during the first half of the planet's history.

Post-fragmentation population structure in a cooperative breeding Afrotropical cloud forest bird: emergence of a source-sink population network.

The impact of demographic parameters on the genetic population structure and viability of organisms is a long-standing issue in the study of fragmented populations. Demographic and genetic tools are now readily available to estimate census and effective population sizes and migration and gene flow rates with increasing precision. Here we analysed the demography and genetic population structure over a recent 15-year time span in five remnant populations of Cabanis's greenbul (Phyllastrephus cabanisi), a cooperative breeding bird in a severely fragmented cloud forest habitat. Contrary to our expectation, genetic admixture and effective population sizes slightly increased, rather than decreased between our two sampling periods. In spite of small effective population sizes in tiny forest remnants, none of the populations showed evidence of a recent population bottleneck. Approximate Bayesian modelling, however, suggested that differentiation of the populations coincided at least partially with an episode of habitat fragmentation. The ratio of meta-Ne to meta-Nc was relatively low for birds, which is expected for cooperative breeding species, while Ne /Nc ratios strongly varied among local populations. While the overall trend of increasing population sizes and genetic admixture may suggest that Cabanis's greenbuls increasingly cope with fragmentation, the time period over which these trends were documented is rather short relative to the average longevity of tropical species. Furthermore, the critically low Nc in the small forest remnants keep the species prone to demographic and environmental stochasticity, and it remains open if, and to what extent, its cooperative breeding behaviour helps to buffer such effects.

Exclusion of vanA, vanB and vanC type glycopeptide resistance in strains of Lactobacillus reuteri and Lactobacillus rhamnosus used as probiotics by polymerase chain reaction and hybridization methods.

Strains of Lactobacillus reuteri and Lact. rhamnosus are used as probiotics in man and animal. The aim of this study was to determine whether the glycopeptide resistance in these lactobacilli has a similar genetic basis as in enterococci. Five Lact. reuteri strains and one Lact. rhamnosus, as well as four Enterococcus control strains, were probed for the vanA gene cluster, the vanB gene and the vanC gene by PCR and Southern hybridization, and DNA/DNA hybridization. Their resistance and plasmid patterns were also investigated. All Lactobacillus strains were resistant to vancomycin but susceptible to a broad range of antibiotics. Four of the Lactobacillus strains (including the Lact. rhamnosus strain) did not harbour any plasmid and two of them contained five and 6 plasmid bands respectively. None of the Lactobacillus strains possessed the vanA, vanB or vanC gene. These findings indicate that the glycopeptide resistance of the Lactobacillus strains analysed is different from the enterococcal type. The study provides reassurance on the safety of the Lactobacillus strains used as probiotics with regard to their vancomycin resistance.

A comparative study of the hemostatic effects of two monophasic oral contraceptives containing 30 mu(g) ethinylestradiol and either 2 mg chlormadinone acetate or 150 mu(g) desogestrel.

OBJECTIVES: To determine the effect of two low-dose monophasic oral contraceptives containing either 2 mg chlormadinone acetate or 150 microg desogestrel on blood clotting and fibrinolysis. METHODS: In vivo markers of intravascular coagulatory and fibrinolytic activity were measured in 45 volunteers randomly assigned to a 6-month treatment with one of the two study preparations. RESULTS: During oral contraceptive use, the procoagulatory activity increased (increased prothrombin fragment 1+2), the anticoagulatory capacity changed (increased protein C activity, decreased activated protein C sensitivity, decreased protein S activity and decreased antithrombin III activity) and the fibrinolytic system was activated (increased concentrations of plasmin-antiplasmin complexes and D-dimer as well as total fibrin degradation products). There were no relevant differences between the two medication groups. CONCLUSION: Our results demonstrate that both oral contraceptive preparations have comparable effects on the hemostatic system. There was a shift towards a new equilibrium of hemostatic activities, both coagulatory and fibrinolytic, at a higher turnover rate. Changes did not exceed the range of normal variation and were comparable to the published effects of other low-dose oral contraceptives. There was no evidence ofa differential risk of deep vein thrombosis between the two preparations.