Structure and conformation in solution of the parallel-stranded hybrid α-d(CGCAATTCGC)·β-d(GCGTTAAGCG) by high-resolution 2D NMR

Summary The unnatural duplex oligonucleotide -d(CGCAATTCGC)·-d(GCGTTAAGCG) was analyzed by high-resolution NMR methods. All of the exchangeable imino and nonexchangeable protons of the duplex were assigned. Detection of all 10 of the exchangeable imino protons confirms that a parallel, unsymmetrical duplex is formed. The thermal stability of the parallel duplex is similar to the analogous antiparallel - duplex. The right handedness of the helix is confirmed by inter-residue [H8/H6-H1] and [H8/H6-H2] NOEs to the 5-neighbor in the -strand and [H8/H6-H1] NOEs to the 3-neighbor in the -strand. Intra-residue and inter-residue distances between base protons and deoxyribose protons in both strands were determined using the isolated spin-pair approximation for NOESY cross peaks acquired with mixing times 50 ms or less. The NOE data are consistent with a B-form geometry adopted by the / hybrid decamer.     

Development of bacterial populations of telluric, enteric, and marine origin in planktonic systems exposed to urban pollution; mathematical data analysis]

A study of the comparative distribution of different types of bacterial populations in the sea area where the city of Marseille rejects its waste water shows that, when in contact with the marine environment, a great part of the allochthonic bacterial population undergoes physiological stress expressed by an abrupt reduction of the effectives and by weak values of the energetic charge. The presence of coliforms and streptococci in waste water lens, at important distances from discharging conduits, shows the possibility of a large diffusion for a fraction of the bacterial populations that withstand the initial stress. From mathematical analyses, an inverse correlation is revealed between detergents and the bacterial population as a whole, and between phenols and various allochthonic bacterial populations. The above results were evidenced through a sampling strategy based upon a 24-h-cycle study and a search for mathematical correlations between several biological, chemical, and physical parameters.     

Pathogeography: leveraging the biogeography of human infectious diseases for global health management

Biogeography is an implicit and fundamental component of almost every dimension of modern biology, from natural selection and speciation to invasive species and biodiversity management. However, biogeography has rarely been integrated into human or veterinary medicine nor routinely leveraged for global health management. Here we review the theory and application of biogeography to the research and management of human infectious diseases, an integration we refer to as ‘pathogeography’. Pathogeography represents a promising framework for understanding and decomposing the spatial distributions, diversity patterns and emergence risks of human infectious diseases into interpretable components of dynamic socio‐ecological systems. Analytical tools from biogeography are already helping to improve our understanding of individual infectious disease distributions and the processes that shape them in space and time. At higher levels of organization, biogeographical studies of diseases are rarer but increasing, improving our ability to describe and explain patterns that emerge at the level of disease communities (e.g. co‐occurrence, diversity patterns, biogeographic regionalisation). Even in a highly globalized world most human infectious diseases remain constrained in their geographic distributions by ecological barriers to the dispersal or establishment of their causal pathogens, reservoir hosts and/or vectors. These same processes underpin the spatial arrangement of other taxa, such as mammalian biodiversity, providing a strong empirical ‘prior’ with which to assess the potential distributions of infectious diseases when data on their occurrence is unavailable or limited. In the absence of quality data, generalized biogeographic patterns could provide the earliest (and in some cases the only) insights into the potential distributions of many poorly known or emerging, or as‐yet‐unknown, infectious disease risks. Encouraging more community ecologists and biogeographers to collaborate with health professionals (and vice versa) has the potential to improve our understanding of infectious disease systems and identify novel management strategies to improve local, global and planetary health.     

Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks

Aim

Habitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non‐native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition.

Location

The species rich and diverse grasslands in the KwaZulu‐Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas.

Results

Flower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA.

Main conclusions

The RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.     

‘Twisted plywood’ structure and mineralization in the scales of a primitive living fish Amia calva

The basal plate of the scales of Amia calva is composed of regular double twisted plywood, as in Latimeria and Dipnoan scales. However, the progressive rotation of the fibrils direction is left-handed in Amia and right-handed in the ‘Sarcopterygians’. So, the similarity between these peculiar plywoods is probably the result of convergence. The basal plate of Amia scales is incompletely mineralized. There are numerous calcified ovoid corpuscles which look very like the Mandl's corpuscles of Teleost scales. The mineralization probably progresses essentially by the fusion of these corpuscles, as in Teleost scales, and would be inotropic rather than spheritic.     

Comparative study of the milk fat globule membrane and the mouse mammary tumour virus prepared from the milk of an infected strain of Swiss albino mice.

Milk fat globule membranes and mammary tumour virus particles (d=1.17 g/cm3) have been obtained from the milk of a Swiss albino mice strain. Comparative biochemistry shows that these two structures differ significantly in the phospholipid, polypeptide and glycopolypeptide patterns and enzymatic activities. However, the lipid profile and the morphology of both structures suggest a filiation with the plasma membrane. Density fractions obtained from the crude virus preparation have been thoroughly investigated. The results suggest that most of these fractions represent degraded virus and/or atypical virus assembly.     

The dipeptide repeat region of the fibrinogen-binding protein (clumping factor) is required for functional expression of the fibrinogen-binding domain on the Staphylococcus aureus cell surface

Clumping factor of Staphylococcus aureus is a fibrinogen-binding protein that is located on the bacterial cell surface. The protein has an unusual repeat domain (region R) comprising mainly the dipeptide aspartate and serine. To determine if region R has a role in the surface display of the fibrinogen-binding region A domain, deletions lacking the region R encoding region of the clfA gene were generated. To determine the minimum length of region R required for wild-type levels of ClfA expression, variants with truncated region R domains were constructed. S. aureus cells expressing mutated clfA genes were tested for (i) proteins released by lysostaphin treatment that reacted with antisera specific for region A, (ii) clumping in soluble fibrinogen, (iii) adherence to immobilized fibrinogen and (iv) expression of the ClfA antigen on the cell surface by fluorescent activated cell sorting analysis. Each construct expressed three major immunoreactive proteins, two of which were putative N-terminal degradation products. Region R residues greater than 40 were required between region A and W (72 residues between region A and the LPDTG sorting signal) for wild-type levels of clumping in fibrinogen. A stepwise decrease in clumping titre was observed as the distance between region A and LPDTG was decreased from 72 to 4 residues. Similarly, a decrease in binding of anti-ClfA serum and in binding to fibrinogen-coated plastic surfaces was observed with cells expressing ClfA with 40 region R residues or less. Nevertheless, low levels of adherence to fibrinogen and binding to anti-ClfA serum occurred with ClfA derivatives that lacked region R altogether. This indicates that a small proportion of the ClfA molecules are linked to peptidoglycan very close to the cell surface but that residues greater than 72 are needed to allow sufficient ClfA molecules to span the entire cell wall and to display the biologically active A domain in a form that can participate fully in fibrinogen binding.     

Effects of dietary manipulations and glucose infusion on glucagon response during exercise in rats

Tadjoré, Maurice, Raynald Bergeron, Martin Latour,François Désy, Claude Warren, and Jean-Marc Lavoie.Effects of dietary manipulations and glucose infusion on glucagonresponse during exercise in rats. J. Appl.Physiol. 83(1): 148-152, 1997.The purpose of thepresent investigation was to test the hypothesis that blood glucoseconcentration is not always related to glucagon response duringexercise. Three groups of rats were submitted to a prolonged (3-h)swimming exercise. Two groups of rats had their normal food intakerestricted by 50% the night before the experiment. One of these twogroups of rats was intravenously infused with glucose throughoutexercise to maintain euglycemia. The third group of rats swam whileunder normal dietary conditions. Plasma glucose, sampled in arterialblood, was reduced (P < 0.05) at 75, 105, 150, and 170 min of exercise (from ~130 to 110 mg/dl) in thefood-restricted animals without glucose infusion, whereas a significant(P < 0.05) increase was measured inthe two other groups during exercise. A significant(P < 0.01) difference in the meanintegrated areas under the glucose-concentration curve was found onlybetween the fed and the two food-restricted groups. Plasma insulinconcentrations decreased (P < 0.05)similarly in all groups during exercise, whereas plasma epinephrine andnorepinephrine concentrations increased significantly(P < 0.01) in all groups. Despitedifferences between groups in plasma glucose response during exercise,and despite the absence of any decrease in exercising blood glucoselevels in at least two of the three groups, plasma glucagon responseswere increased (P < 0.05) similarlyin all groups (from ~250 to 550 pg/ml) at the end of the exerciseperiod. The increase in glucagon was significant after 90 min ofexercise in the food-restricted groups, with or without glucoseinfusion, but only after 140 min in the fed group. These resultsindicate that the glucagon response during exercise is not alwayslinked to the decrease in plasma glucose.