Bryozoaires des milieux récifaux miocèes du sillon sud-rifain au Maroc

Moissette, P. & Saint Martin, J_:P. 1995 11 30 Bryozoaires des milieux récifaux miocenes du sillon sud-rifain au Maroc. [Bryozoans from Miocene reef environments in the South-Rifian corridor of Morocco. In late Miocene coral reefs from the Fes area (Northern Morocco), bryozoans are the best-represented group. An inventory of the bryozoan fauna (59 species) was taken on two reefs with different organization and palaeogeographical situation in a late Miocene seaway between the Atlantic and the Mediterranean. A study of the bryozoans and their zoarial forms allows an improved reconstruction of reefal environments and available habitats. Membraniporiforrn (encrusting) colonies largely predominate, whereas celleporiforms (nodular colonies) are more rare. Rigid erect (vinculariiform, adeoniform, and reteporiform) and rigid articulated zoarial types (cellariiform and catenicelliform) are fairly well represented. At depths of about 10 m and on the reef front encrusting bryozoans were well developed in cryptic habitats on living coral substrates. Erect species lived in cavities provided by the coral framework, and plants offered flexible substrates for the attachment of epiphytal forms. □Bryozoa, coral reefs, Morocco, Messininn, pulueoecology. Dans les récifs coralliens du Miocène supérieur de la région de Fes (Maroc septentrional), les bryozoaires constituent, parrni les organismes conservés, le groupe le mieux représenté. Un recensement de la fame de bryozoaires (59 espèces) a été effectué dans deux récifs d'organisation et de situation paléogéographique différentes, dans un secteur de communication entre Atlantique et Méditerranée au MiocéFne supérieur. L'étude des bryozoaires et de leurs formes zoariales permet de proposer une meilleure reconstitution de I'environnement récifal et des habitats disponibles. Les colonies membraniporiformes (encrobtantes) predominent largement, alors que les cellepori-formes (colonies noduleuses) sont beaucoup plus rares. Les types zoariaux érigés rigides (vincula-riiforme, adéoniforme et rétéporiforme) et érigés articulés (cellariiforme et catenicelliforme) sont assez bien représentés. A des profondeurs denviron 10 m et dans la partie antérieure des constructions récifales, les bryozoaires encroûtants étaient bien développés dans des habitats cryptiques sur substrats coralliens vivants. Des formes dressées vivaient dans les cavités ménagées par le bâti corallien et des supports végétaux permettaient également la fixation de formes épiphytes. □Bryozouires, récifs coralliens, Muroc, Messinien, puléoécologie.     

The chaperone/usher pathway: a major terminal branch of the general secretory pathway

Gram-negative bacteria assemble a variety of adhesive organelles on their surface, including the thread-like structures known as pili. Recent studies on pilus assembly by the chaperone/usher pathway have revealed new insights into the mechanisms of pilus subunit export into the periplasm and targeting to the outer membrane. Signaling events controlling pilus biogenesis have begun to emerge and investigations of the usher have yielded insights into pilus translocation across the outer membrane.     

Development of a transient large strain contact method for biological heart valve simulations

A new 2D method to implement transient contact using Comsol Multiphysics (finite element analysis software that enables multiphysics simulations) is described, which is based on Hertzian contact. This method is compared to the existing (default) contact method that does not enable real transient simulations, but instead performs steady-state solutions where time is a constant. The two types of contact modelling have been applied to simple 2D biological heart valve models, undergoing strains in the region of 10% under 20 kPa pressure (applied over 0.3 s). Both the methods predicted comparable stress patterns, locations of peak stresses, deformations and directions of principal stress. The default contact method predicted slightly greater contact stresses, but spreads over a shorter surface length than the new contact method. The default contact method is useful for contact systems with little transient dependency, due to ease of use. However, where transient conditions are important the new contact method is preferred.     

Identification of land predators of African Penguins Spheniscus demersus through post-mortem examination

The African Penguin Spheniscus demersus is an endangered seabird endemic to southern Africa, and killing sprees by terrestrial predators have been one of the main threats for its mainland colonies. The methods employed to manage predators may differ depending on the species involved, therefore the implementation of strategies to limit the impacts of predation relies on the correct identification of the culprit predator. We report and quantify the lesions seen in African Penguins killed by four species of terrestrial predators: Caracal Caracal caracal (52 kills), Leopard Panthera pardus (27 kills), Domestic Dog Canis lupus familiaris (10 kills), and Cape Grey Mongoose Galerella pulverulenta (4 kills). We discuss patterns of necropsy findings that can be used to identify the predator species involved. Traditional forensic methods are useful tools to direct species-specific management actions for the conservation of the African Penguin and other seabirds so that effective mitigating measures can be deployed quickly to prevent further losses. It should be borne in mind, however, that the age, size and previous hunting experience of the predator are likely to influence the pattern of lesions that will be observed, and not all carcasses will have hallmark lesions or recognisable bite marks.     

Fermentation characterization and flux analysis of recombinant strains of Clostridium acetobutylicum with an inactivated solR gene

The effect of solR inactivation on the metabolism of Clostridium acetobutylicum was examined using fermentation characterization and metabolic flux analysis. The solR-inactivated strain (SolRH) of this study had a higher rate of glucose utilization and produced higher solvent concentrations (by 25%, 14%, and 81%, respectively, for butanol, acetone, and ethanol) compared to the wild type. Strain SolRH(pTAAD), carrying a plasmid-encoded copy of the bifunctional alcohol/aldehyde dehydrogenase gene (aad) used in butanol production, produced even higher concentrations of solvents (by 21%, 45%, and 62%, respectively, for butanol, acetone, and ethanol) than strain SolRH. Clarithromycin used for strain SolRH maintenance during SolRH(pTAAD) fermentations did not alter product formation; however, tetracycline used for pTAAD maintenance resulted in 90% lower solvent production. Journal of Industrial Microbiology & Biotechnology (2001) 27, 322–328. Received 12 September 2000/ Accepted in revised form 21 July 2001     

A high-throughput microscale method to release N-linked oligosaccharides from glycoproteins for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis

This report describes a convenient method for the rapid and efficient release of N-linked oligosaccharides from low microgram amounts of glycoproteins. A 96-well MultiScreen assay system containing a polyvinylidene difluoride (PVDF) membrane is employed to immobilize glycoproteins for subsequent enzymatic deglycosylation. Recombinant tissue-type plasminogen activator (rt-PA) is used to demonstrate the deglycosylation of 0.1-50 micrograms of a glycoprotein. This method enabled the recovery of a sufficient amount of N-linked oligosaccharides released enzymatically with peptide N-glycosidase F (PNGaseF) from as little as 0.5 microgram rt-PA for subsequent analysis by matrix-assisted laser desorption/ionization time-of-flight (MALDI- TOF) mass spectrometry. The immobilization of rt-PA to the PVDF membrane did not sterically inhibit the PNGaseF-mediated release of oligosaccharides from rt-PA as determined by tryptic mapping experiments. Comparison of the oligosaccharides released from 50 micrograms of rt-PA by either the 96-well plate method or by a standard solution digestion procedure showed no significant differences in the profiles obtained by high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Both neutral and sialylated oligosaccharide standards spiked into wells were recovered equally as determined by HPAEC-PAD. One advantage of this approach is that reduction and alkylation can be performed on submicrogram amounts of glycoproteins with easy removal of reagents prior to PNGaseF digestion. In addition, this method allows 60 glycoprotein samples to be deglycosylated in 1 day with MALDI-TOF or HPAEC-PAD analysis being performed on the following day.      

Ramifications of kinetic partitioning on usher-mediated pilus biogenesis.

The biogenesis of diverse adhesive structures in a variety of Gram-negative bacterial species is dependent on the chaperone/usher pathway. Very little is known about how the usher protein translocates protein subunits across the outer membrane or how assembly of these adhesive structures occurs. We have discovered several mechanisms by which the usher protein acts to regulate the ordered assembly of type 1 pili, specifically through critical interactions of the chaperone-adhesin complex with the usher. A study of association and dissociation events of chaperone-subunit complexes with the usher in real time using surface plasmon resonance revealed that the chaperone-adhesin complex has the tightest and fastest association with the usher. This suggests that kinetic partitioning of chaperone-adhesin complexes to the usher is a defining factor in tip localization of the adhesin in the pilus. Furthermore, we identified and purified a chaperone-adhesin-usher assembly intermediate that was formed in vivo. Trypsin digestion assays showed that the usher in this complex was in an altered conformation, which was maintained during pilus assembly. The data support a model in which binding of the chaperone-adhesin complex to the usher stabilizes the usher in an assembly-competent conformation and allows initiation of pilus assembly.     

The influence of water level on macrophyte growth and trophic interactions in eutrophic Mediterranean shallow lakes: a mesocosm experiment with and without fish

1. Water‐level fluctuations are typical of lakes located in the semi‐arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial. 2. In eutrophic Lake Eymir, Turkey, we conducted a 4‐month (summer) field experiment using cylindrical 0.8‐m‐ (low‐water‐level) and 1.6‐m‐deep (high‐water‐level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm. 3. Sampling for physicochemical variables, chlorophyll a (chl‐a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m. 4. Throughout the experiment, fish affected zooplankton abundance (?), nutrient concentrations (+), chl‐a (+) and water clarity (?) most strongly in the low‐water‐level mesocosms and the zooplankton community shifted towards dominance of small‐sized forms. The fishless mesocosms had a higher zooplankton/phytoplankton ratio, suggesting higher grazing. 5. Greatest macrophyte growth was observed in the low‐water‐level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water‐level decrease from midsummer onwards. Macrophyte growth was poor in the high‐water‐level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes. 6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top‐down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.     

Gut microbiome composition and function in experimental colitis during active disease and treatment-induced remission

Dysregulated immune responses to gut microbes are central to inflammatory bowel disease (IBD), and gut microbial activity can fuel chronic inflammation. Examining how IBD-directed therapies influence gut microbiomes may identify microbial community features integral to mitigating disease and maintaining health. However, IBD patients often receive multiple treatments during disease flares, confounding such analyses. Preclinical models of IBD with well-defined disease courses and opportunities for controlled treatment exposures provide a valuable solution. Here, we surveyed the gut microbiome of the T-bet^−/− Rag2^−/− mouse model of colitis during active disease and treatment-induced remission. Microbial features modified among these conditions included altered potential for carbohydrate and energy metabolism and bacterial pathogenesis, specifically cell motility and signal transduction pathways. We also observed an increased capacity for xenobiotics metabolism, including benzoate degradation, a pathway linking host adrenergic stress with enhanced bacterial virulence, and found decreased levels of fecal dopamine in active colitis. When transferred to gnotobiotic mice, gut microbiomes from mice with active disease versus treatment-induced remission elicited varying degrees of colitis. Thus, our study provides insight into specific microbial clades and pathways associated with health, active disease and treatment interventions in a mouse model of colitis.