Sequence of a gene encoding a (poly ManA) alginate lyase active on Pseudomonas aeruginosa alginate

Abstract To overcome problems associated with Western blotting of denatured proteins, we have used quantitative immunoelectrophoretic techniques to perform functional analysis of the Neisseria gonorrhoeae common antigen. Using these techniques, we show (a) that Neisseria gonorrhoeae expresses an antigen that is cross-reactive with the common antigen of Pseudomonas aeruginosa and Legionella micdadei and with the GroEl-like protein of Chlamydia , and (b) that this N. gonorrhoeae common antigen has lectin-like activity and can be precipitated with three different sugars immobilized on agarose beads: α- d -glucosamine, maltose and fucose.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

Influence of subantarctic Macrocystis bed metabolism in diel changes of marine bacterioplankton and CO2 fluxes

The significance of bacterial communities in the fluxes of carbonand energy in giant kelp beds (Macrocystis pyrifera) in KerguelenArchipelago, subantarctica, was estimated by measuring bacterioplanktonbiomass and production over diel cycles in surface seawaterslocated inside and outside of Macrocystis beds. Several physicochemicalparameters [temperature, solar radiation, tide level, dissolvedoxygen, total inorganic carbon (TCO₂), partial pressure of CO₂(pCO₂) and dissolved organic carbon (DOC)] were simultaneouslyrecorded in order to establish possible relationships with observedchanges in bacterial parameters. Bacterial biomass and productionwere significantly higher inside the kelp bed than in the surroundingarea. Furthermore, the results showed large and clear diel variationsof all parameters measured inside the kelp bed. Changes in dissolvedoxygen, TCO₂ and pCO₂ paralleled those of solar radiation, andwere obviously related to the metabolic activity of the kelp.Mean cell volumes and saprophytic bacterial abundance variedover the diel cycles in the same way as photosynthetic activity,while DOC, bacterioplankton production and the frequency ofdividing cells varied in an opposite way with maximal valuesat night-time.     

From Metaphor to Measurement: Resilience of What to What?

Resilience is the magnitude of disturbance that can be tolerated before a socioecological system (SES) moves to a different region of state space controlled by a different set of processes. Resilience has multiple levels of meaning: as a metaphor related to sustainability, as a property of dynamic models, and as a measurable quantity that can be assessed in field studies of SES. The operational indicators of resilience have, however, received little attention in the literature. To assess a system's resilience, one must specify which system configuration and which disturbances are of interest. This paper compares resilience properties in two contrasting SES, lake districts and rangelands, with respect to the following three general features: (a) The ability of an SES to stay in the domain of attraction is related to slowly changing variables, or slowly changing disturbance regimes, which control the boundaries of the domain of attraction or the frequency of events that could push the system across the boundaries. Examples are soil phosphorus content in lake districts woody vegetation cover in rangelands, and property rights systems that affect land use in both lake districts and rangelands. (b) The ability of an SES to self-organize is related to the extent to which reorganization is endogenous rather than forced by external drivers. Self-organization is enhanced by coevolved ecosystem components and the presence of social networks that facilitate innovative problem solving. (c) The adaptive capacity of an SES is related to the existence of mechanisms for the evolution of novelty or learning. Examples include biodiversity at multiple scales and the existence of institutions that facilitate experimentation, discovery, and innovation. Received 20 March 2001; accepted 6 June 2001.     

Influence de quelques paramètres du milieu d'incubation sur la survie d'alevins de saumon atlantique,Salmo salar L., en ruisseau expérimental. Influence of some Environmental Parameters upon Survival during Embryonic Development of Atlantic salmon,Salmo solar L., in an Experimental Stream Channel

The effect of some environmental parameters of the redd (substrate composition, interstitial dissolved oxygen concentration) upon survival of Atlantic salmon embryos was studied in a large artificial stream channel. Batches of 3000 eyed eggs were buried 0.25 m deep in the gravel substrate of 8 different channel sections, where natural or artificial sediment deposition took place. Upon emergence, fry were captured in drift nets or by electrofishing. Survival varied from 32 to 94 % in the different sections. It was strongly affected by volume of sediment less than 10 mm in particle size and more particularly by the fraction less than 0.2 mm, the main component of natural sediment deposition. Survival was less strongly determined by oxygen concentration variations except for values less than 2 mg/l obtained in the section with highest sediment deposition. Available volume of interstitial void space appeared to be crucial for good survival during larval development.