ExbB acts as a chaperone-like protein to stabilize TonB in the cytoplasm

The TonB protein is required to transduce energy from the cytoplasmic membrane to outer membrane transport proteins of Gram-negative bacteria. Two accessory proteins, ExbB and ExbD, are required for TonB function and it has been suggested that TonB and ExbBD form a complex in the membrane. In this paper we demonstrate that there are two spatially distinct, functional interactions between ExbBD and TonB. First, there is an interaction between ExbBD and the N-terminal signal-like peptide of TonB, probabiy the formation of a stable complex in the membrane. Second, ExbB interacts with TonB in the cytoplasm. This interaction involves the domain of TonB that is normally periplasmic. Thus, this is a transient interaction which occurs during the synthesis and/or localization of TonB, implying a chaperone-like role for ExbB. The transmembrane topology of ExbB was shown to be consistent with this role.     

THE HOLY GRAIL OF THE PERFECT CHARACTER: THE CLADISTIC TREATMENT OF MORPHOMETRIC DATA

Abstract— Data scored for cladistic analyses may be quantitative or qualitative, continuous or discrete, and show overlapping or non-overlapping values between taxa. Quantitative and qualitative are modes of expression of data, while continuous or discrete refer to properties of the set of numbers that express the data; both these pairs of terms have been confused with overlapping and non-overlapping. The degree of overlap of values between taxa is often used to filter characters in cladistic analyses: if a minimum amount of overlap is exceeded, or a minimum amount of disjunction not reached, characters are rejected as "not cladistic". However, this rests on a confusion between features of taxa and features of individual organisms (attributes). Cladistic characters are features of taxa, and comprise frequency distributions of attribute values over individuals of a taxon. Cladistic characters logically cannot overlap, although taxa may have overlapping attribute values. Thus, a priori rejection of characters that have overlapping attribute values is non-sensical. Such data may still be rejected from consideration for cladistic analysis if it could be demonstrated that they contain little recoverable phylogenetic signal. Few published analyses have empirically tested this. An analysis of overlapping morphometric data from three series of Banksia suggests that, at least in these cases, they map phylogeny almost as accurately as more conventional, qualitative morphological data. While more such tests are required, morphometric data should not be rejected a priori from cladistic analyses.     

Parthenogenesis in an elasmobranch in the presence of conspecific males

Parthenogenesis has been observed in several elasmobranch species, primarily in public aquaria. The majority of cases of parthenogenesis have occurred either when females were held without males or once a male was removed from a female's habitat. Here we report a second instance of parthenogenesis in a zebra shark female that was housed with conspecific mature males. This study calls into question the conditions under which elasmobranch females undergo parthenogenesis.     

Enzymology in vivo using NMR and molecular genetics

Models of metabolic flux regulation are frequently based on an extrapolation of the kinetic properties of enzymes measured in vitro to the intact cell. Such an extrapolation assumes a detailed knowledge of the intracellular environment of these enzymes in terms of their free substates and effectors concentrations and possible interaction with other cellular macromolecules, which may modify their kinetic properties. These is a considerable incentive, therefore, to study the properties of enzymes directly in vivo. We have been using non-invasive NMR techniques, in conjunction with molecular genetic manipulation of enzyme levels, to study the kinetic properties of individual enzymes in vivo. We have also developed a novel strategy which has allowed us to monitor, by NMR, the ligand binding properties and mobilities of enzymes in the intact cell. This technique may also allow us to measured the diffusion coefficients of these proteins in the cell. These studies should give new insight into the properties of enzymes in vivo     

THE COMPOSITION AND PHYLOGENETIC SIGNIFICANCE OF THE MOUGEOTIA (CHAROPHYCEAE) CELL WALL1

The two-layered, fibrillar cell wall of Mougeotia C. Agardh sp. consisted of 63.6% non-cellulosic carbohydrates and 13.4% cellulose. The orientation of cellulose microfibrils in the native cell wall agrees with the multinet growth hypothesis, which has been employed to explain the shift in microfibril orientation from transverse (inner wall) toward axial (outer wall). Monosaccharide analysis of isolated cell walls revealed the presence of ten sugars with glucose, xylose and galactose most abundant. Methylation analysis of the acid-modified, 1 N NaOH insoluble residue fraction showed that it was composed almost exclusively of 4-linked glucose, confirming the presence of cellulose. The major hemicellulosic carbohydrate was semi-purified by DEAE Sephacel (Cl^?) anion-exchange chromatography of the hot 1 N NaOH soluble fraction. This hemicellulose was a xylan consisting of a 4-xylosyl backbone and 2,4-xylosyl branch points. The major hot water soluble neutral polysaccharide was identified as a 3-linked galactan. Mougeotia cell wall composition is similar to that of (Charophyceae) and has homologies with vascular plant cell walls. Our observations support transtructural evidence which suggests that members of the Charophyceae represent the phylogenetic line that gave rise to vascular plants. Therefore, the primary cell walls of vascular plants many have evolved directly from structures typical of the filamentous green algal cell walls found in the Charophyceae.     

The ecosystem approach to environmental assessment: moving from theory to practice

The ecosystem approach to environmental management is viewed by many as being fundamental to the development of appropriate management strategies. While this approach represents a major advance in the way researchers view environmental assessment, the approach in itself does not provide practical information as to what questions to ask and what tools to use in assessing and managing ecosystems. Similarly, the concept of ecosystem health, as it is usually defined, has little practical value for ecosystem managers. We suggest the next stage in environmental assessment will be the development of specific frameworks designed to assess individual ecosystems. Of primary importance is the need to consider the basic structure and function of the ecosystem itself. Such consideration, together with explicit identification of anthropogenic stresses particular to the system, serves to identify those components most at risk and those issues most deserving of attention. Researchers should explore critical linkages between environmental stressors and their observable, measurable and predictable effects on ecological parameters and use this understanding to develop a management strategy that incorporates appropriate ecological indicators. The importance of these considerations will be illustrated using examples from the Northern River Basins Study.     

Utility of field-based artificial streams for assessing effluent effects on riverine ecosystems

Experimentation using field-based artificial streams provides a promising, complimentary approach to biomonitoring assessments because artificial streams provide control over relevant environmental variables and true replication of treatments. We have used large and small artificial stream systems, based in the field, to examine the effect of treated bleached kraft pulp mill effluent (BKME) on the benthos of three large rivers in western Canada. Under natural regimes of temperature, water chemistry, and insolation, these artificial streams provide current velocities and substrata to food chains or food webs that are representative of those in the study river. With these tools we have shown that BKME stimulated mayfly growth in the Thompson River above that which could be accounted for by fertilization of their algal food supply. In contrast, moulting frequency was inhibited at high BKME concentrations. Results from artificial streams also indicate that increased algal biomass and abundances of benthic communities downstream of BKME outfalls were induced by nutrient enrichment from the effluent. BKME treatments did not change diatom species richness in the Fraser River, or diatom species diversity in either the Athabasca or Fraser Rivers. Artificial streams provide a means of understanding the mechanisms of stressor effects over a continuum ranging from single stressor effects on specific taxa to the effects of multiple stressors on communities and ecosystems. Because riverside deployment provides environmental realism within a replicated experimental design, this approach can (i) address questions that cannot be examined using laboratory tests or field observations, (ii) improve our mechanistic understanding of stressor effects on riverine ecosystems, and (iii) can contribute directly to the development, parameterization, and testing of models for predicting ecosystem-level responses.     

Evidence that predator satiation may restrict the spatial spread of a tussock moth (Orgyia vetusta) outbreak

Western tussock moths (Orgyia vetusta Bdv., Lymantriidae) infest one stand of bush lupine (Lupinus arboreus Sims, Fabaceae) heavily and several other stands very lightly at the Bodega Marine Reserve (Sonoma Co., Calif., USA). We found that the disappearance rates of experimentally placed larvae and pupae were consistently lower in the outbreak area than in non-outbreak areas. For pupae but not larvae, this difference was removed by using tanglefoot to repel nonflying predators. However, the major nonflying predator of pupae, the ant Formica lasioides, was no more abundant in non-outbreak areas than in the outbreak area. We found inverse density-dependence in the rate of attack by F. lasioides on experimental pupae, suggesting this generalist predator is satiated within the outbreak area, but preys more heavily on the moth where the moth is sparse.