Successful invasion of a food web in a chemostat

A food web in a chemostat is considered in which an arbitrary number of competitor populations compete for a single, essential, nonreproducing, growth-limiting substrate, and an arbitrary number of predator populations prey on some or all of the competitor populations. Although any number of predator populations may prey on the same competitor population, each predator population preys on only one competitor population. The dynamics of substrate uptake is modeled by Lotka-Volterra or Michaelis-Menten (Holling type I or II), but the dynamics of competitor uptake is restricted to Lotka-Volterra. Based on certain parameters, the model predicts the asymptotic survival or extinction of each of the different populations and suggests how competitor and/or predator populations could successfully invade the chemostat with or without causing a diverse ecosystem to crash. Similarly, it suggests how the elimination of certain populations could result in a more diverse or less diverse system.     

Competition intensity along a productivity gradient in a low-diversity grassland

Competition among plants often shifts from roots to shoots as productivity increases and species composition changes. We examined competition in an old field with low diversity to test whether this shift occurred along a productivity gradient without species turnover. Forty plots received one of four nitrogen treatments (0, 5, or 15 g added N m-2 yr-1 or 400 g m-2 yr-1 of sawdust added to immobilize N) annually for 5 yr. All N levels were dominated by the perennial grasses Agropyron cristatum and Bromus inermis. Transplants of Agropyron were grown with all neighbors, roots of neighbors, or no neighbors present to measure total, root, and shoot competition. Transplant growth was 22%-165% higher in subplots without neighbors present, which indicates that competition occurred. Competition from neighbor roots was primarily responsible for suppression of transplant growth over the entire productivity gradient. In contrast to previous field experiments that found either an increase in total competition intensity or a shift from root to shoot competition with increasing productivity, we found neither. Increases in total competition intensity or shifts from root to shoot competition found along other gradients may be caused by changes in species composition and not by increased resources or neighbor biomass. These results suggest that different competitive mechanisms may operate in low-diversity vegetation than in more diverse natural vegetation.     

Smoke as a germination cue: a review

Slow combustion or burning of dry or green plant material from many sources produces volatile compounds that are water soluble and that stimulate the germination of many seeds with different dormancy strategies. The active principals are apparently produced around 160ndash;200 deg;C and are volatilized at higher temperatures. Once dissolved in water the active compounds also stimulate rooting, seedling growth and flowering. The positive effects of smoke have resulted in it being used as a seed pre-treatment for enhancing conservation of threatened or rare species, the horticultural exploitation of desirable plants and in the reclamation of mine spoils and disturbed land. Presently the identity of the active molecules is unknown but their remarkable effect on seed germination is, already widely utilized.     

Fixation probability for a beneficial allele and a mutant strategy in a linear game under weak selection in a finite island model

The effect of population structure on the probability of fixation of a newly introduced mutant under weak selection is studied using a coalescent approach. Wright's island model in a framework of a finite number of demes is assumed and two selection regimes are considered: a beneficial allele model and a linear game among offspring. A first-order approximation of the fixation probability for a single mutant with respect to the intensity of selection is deduced. The approximation requires the calculation of expected coalescence times, under neutrality, for lineages starting from two or three sampled individuals. The results are obtained in a general setting without assumptions on the number of demes, the deme size or the migration rate, which allows for simultaneous coalescence or migration events in the genealogy of the sampled individuals. Comparisons are made with limit cases as the deme size or the number of demes goes to infinity or the migration rate goes to zero for which a diffusion approximation approach is possible. Conditions for selection to favor a mutant strategy replacing a resident strategy in the context of a linear game in a finite island population are addressed.     

Detection of lipopolysaccharide and lipid a employing a spermine-pyrene conjugate

An amphiphilic fluorescent spermine-pyrene conjugate (Sp-Py) is shown to interact with lipopolysaccharide (LPS) or lipid A in aqueous solution. This complexation was studied by UV/visible absorption and steady-state fluorescence spectroscopy. In the presence of LPS or lipid A, Sp-Py displayed self-aggregation, resulting in the appearance of chromophore dimer absorption and fluorescence at the expense of probe monomer features. The equivalent weight of LPS or lipid A and the binding constants for Sp-Py complexation were estimated. The change of the ratio of monomer to dimer emission with concentration of LPS or lipid A indicated that Sp-Py is a sensitive fluorescence probe for the endotoxins in aqueous media.     

Enzymatic glycosylation of reducing oligosaccharides linked to a solid phase or a lipid via a cleavable squarate linker.

Reducing oligosaccharides were converted into their corresponding glycosylamines, and these were reacted with 3,4-diethoxy-3-cyclobuten-1,2-dione (squaric acid diethyl ester). The resulting derivatives could be linked to amino-functionalized lipids, solids, or proteins. Treatment of the obtained lipid or solid conjugates with aqueous bromine or, alternatively, with ammonia-ammonium borate cleaved the linkage and regenerated the oligosaccharide glycosylamines, which were in turn rapidly hydrolyzed to the reducing oligosaccharides. To demonstrate the usefulness of this linkage in enzymatic oligosaccharide synthesis, lactose was linked to a lipid or a solid phase, the obtained conjugates were then subjected to two enzymatic glycosylations (either consecutively or 'one-pot'). The resulting materials were then cleaved to give, in both cases, the expected reducing tetrasaccharide (lacto-N-neotetraose) in good yield.     

Detection of a Target Taste in a Complex Masker

Detection thresholds for sodium chloride were compared in aqueoussolution, in mixture with a sucrose masker, in mixture witha citric acid masker, and in mixture with both of these maskerstogether. Separately the two maskers raised the threshold ofsodium chloride by three to four times, and together by overnine times, a result consistent with independence (additivity)of the two masking effects. To achieve comparable masking witheither sucrose alone or with citric acid alone would requireincreasing their masking concentrations by about ten times.Hence multiple masking can be a far more efficient means ofconcealing a taste, whether an unpleasant one (e.g. the bittertaste of medicine) or a pleasant one (e.g. a salty or sweetcondiment). Multiple masking has dietary and culinary significance,especially for middle aged and elderly persons concerned aboutsalt intake, because their thresholds for NaCl, whether withor without maskers, are typically two or three times higherthan those of youthful persons. Chem. Senses 22: 529–534,1997.     

Living off a fish: a trade-off between parasites and the immune system

Research in fish immune system and parasite invasion mechanisms has advanced the knowledge of the mechanisms whereby parasites evade or cope with fish immune response. The main mechanisms of immune evasion employed by fish parasites are reviewed and considered under ten headings. 1) Parasite isolation: parasites develop in immuno-privileged host tissues, such as brain, gonads, or eyes, where host barriers prevent or limit the immune response. 2) Host isolation: the host cellular immune response isolates and encapsulates the parasites in a dormant stage without killing them. 3) Intracellular disguise: typical of intracellular microsporidians, coccidians and some myxosporeans. 4) Parasite migration, behavioural and environmental strategies: parasites migrate to host sites the immune response has not yet reached or where it is not strong enough to kill them, or they accommodate their life cycles to the season or the age in which the host immune system is down-regulated. 5) Antigen-based strategies such as mimicry or masking, variation and sharing of parasite antigens. 6) Anti-immune mechanisms: these allow parasites to resist innate humoral factors, to neutralize host antibodies or to scavenge reactive oxygen species within macrophages. 7) Immunodepression: parasites either suppress the fish immune systems by reducing the proliferative capacity of lymphocytes or the phagocytic activity of macrophages, or they induce apoptosis of host leucocytes. 8) Immunomodulation: parasites secrete or excrete substances which modulate the secretion of host immune factors, such as cytokines, to their own benefit. 9) Fast development: parasites proliferate faster than the ability of the host to mount a defence response. 10) Exploitation of the host immune reaction. Knowledge of the evasion strategies adopted by parasites will help us to understand host-parasite interactions and may therefore help in the discovery of novel immunotherapeutic agents or targeted vaccines, and permit the selection of host-resistant strains.     

Enzyme-mediated site-specific antibody-protein modification using a ZZ domain as a linker

A ZZ domain (ZZ) and alkaline phosphatase (AP), luciferase (Luc), or glucose oxidase (GOD) were conjugated using Sortase A (SrtA) from Staphylococcus aureus. The specific peptidyl linker for SrtA was genetically fused to the C-terminus of ZZ, and the other linker was fused to the N-terminus of AP, Luc, or GOD, respectively. The resultant proteins were obtained separately by bacterial expression. The recombinant peptide-tagged ZZ and AP, Luc, or GOD were site-specifically conjugated by SrtA through the extra peptidyl linkers in vitro. The SrtA reaction had little influence on either the antibody-binding activity of the ZZ moiety or the enzymatic activity of AP, Luc, or GOD moieties of the conjugates. Additionally, antibody-ZZ-proteins were yielded easily by mixing antibody with ZZ-AP, ZZ-Luc, or ZZ-GOD, allowing their use in an enzyme-linked immunosorbent assay. These results suggest that the enzymatic approach with SrtA facilitates the construction of ZZ-proteins. Furthermore, mixing antibody and ZZ-proteins produces a wide variety of antibody-ZZ-proteins.     

Growth of a yeast mutant on ring a modified cholesterol derivatives

The ability of cholesterol derivatives without a hydroxyl group or a side-chain, to support the growth of heme and cyclase deficient Saccharomyces cerevisiae mutant GL 7 was tried and found to be in conformity with the results obtained using liposomes. On the other hand, results with other Ring A modified steroids involving saturation or movement of C5-C6 double bond, or isomeric 3-hydroxy-3-methyl cholestane derivatives, indicated that even minor structural variations can cause considerable changes in their growth supporting potential. The consequence of such structural variations need not be obviated by studies using liposomes or vesicles.     

Intrachromosomal insertions: a case report and a review

Summary We describe the phenotype of a child having a recombinant chromosome 3 with a duplication 3q13.2 q25 derived from a paternal inv ins(3)(p25.3q25q13.2). A review of 27 reported cases of intrachromosomal insertions has revealed that for a carrier of intrachromosomal insertion the risk of a child with an unbalanced karyotype is 15%. This risk may be higher for particular insertions. The recombinant chromosome can have a duplication or a deletion of different segments depending on whether the insertion is direct or inverted, paracentric or pericentric, and whether there is meiotic crossing over in the inserted or the interstitial non-inserted segment. Several of the insertions have been difficult to interpret and some of them have been mistaken for paracentric inversions. Caution is therefore indicated in interpreting parental karyotypes of a child with a deletion or a duplication, particularly if it is interstitial. This is because, whereas a risk of recurrence of a child with an unbalanced karyotype is low in de novo cases and for carriers of paracentric inversions, it is high for carriers of insertions.     

Noninvasive diagnosis of a single cell with a probe beam

It is important to distinguish a living/dead cell in cell culture, especially in the regenerate medicine field including cell therapy, since those cells are usually in short supply and consequently the ex vivo culture process should be operated strictly. Conventional methods for distinguishing a living from a dead cell usually require labeling with a dye, which spoils the culture of the cell. Here we show a simple noninvasive method for diagnosing a dead or alive cell with a probe beam. If a cell is alive, the active transport of materials across the cell membrane causes a change of concentration gradients, and this change further induces a change of deflection of a probe beam passing through a vicinity of the cell membrane. If a cell is dead, no or little change in deflection of the probe beam is induced because no or little active materials movement across the cell membrane exists. The deflection of the probe beam is monitored, and judgment on whether a cell is dead or alive from the deflection signal agreed with the conventional decision.     

Aeromonas salmonicida-secreted protein AopP is a potent inducer of apoptosis in a mammalian and a Drosophila model

Some pathogens are able to establish themselves within the host because they have evolved mechanisms to disrupt host innate immunity. For example, a number of pathogens secrete preformed effector proteins via type III secretion apparatuses that influence innate immune or apoptotic signalling pathways. One group of effector proteins that usurp innate immune signalling is the YopJ-like family of bacterial effector proteins, which includes AopP from Aeromonas salmonicida. Aeromonas species are known to cause gastrointestinal disease in humans, and are associated mainly with subcutaneous wound infections and septicaemia in other metazoans, particularly fish. AopP has been reported to have inhibitory activity against the NF-κB pathway in cultured cells, although the pathological outcomes of AopP activity have not been examined. Here, we show that AopP has potent pro-apoptotic activity when expressed in cultured mammalian macrophage or epithelial cells, or when ectopically expressed in Drosophila melanogaster haemocytes or imaginal disk epithelial cells. Furthermore, apoptosis was significantly elevated upon concurrent AopP expression and TNF-α cellular stimulation. Together, our results demonstrate how the specificity of a YopJ-like protein towards signalling pathways directly governs cellular pathological outcome in disease.     

Chaperone-assisted folding of a single-chain antibody in a reconstituted translation system

A protein-synthesizing system based on a minimal set of purified components was used to investigate the roles molecular chaperones play in the folding of newly synthesized polypeptides. After we ascertained that this system lacks intrinsic chaperones, the effect of adding chaperones in a co-translational or post-translational manner was directly evaluated. An aggregation-prone single-chain antibody was used as the model nascent chain. The participation of the trigger factor or the DnaK system during translation efficiently increased the level of functional protein that was generated. In addition, both systems also acted as chaperones after translation had been stopped. In contrast, the GroEL/ES system showed little or no co- or post-translational assistance in folding.     

棉花根际固氮菌、解磷菌及解钾菌的相互作用

目的通过对棉花根际促生细菌N2126、P1108和K2116菌株单独接种和混合接种,根据这些菌株的固氮、解磷、解钾能力和细胞数量的变化,了解它们之间的相互作用。方法将这3株菌株设置4个不同的组合:N2126+P1108、P1108+K2116、N2126+K2116及N2126+P1108+K2116,分别测定培养液中全氮含量,水溶性磷、钾含量和细胞数量。结果P1108对N2126的生长有促进作用但抑制K2116的生长,N2126和K2116之间存在拮抗作用。N2126、P1108和K2116混合培养后,三者细胞数量分别占培养液中细胞总数的6.4%、89.2%和4.4%;培养液中的全氮含量比不接种时下降了0.7%;水溶性磷、钾含量比不接种时分别增加了19.0%和12.2%。结论P1108为3株菌株混合培养时的优势菌株,3株菌株混合培养有助于磷、钾释放。     

Effects of a disease affecting a predator on the dynamics of a predator-prey system

We study the effects of a disease affecting a predator on the dynamics of a predator-prey system. We couple an SIRS model applied to the predator population, to a Lotka-Volterra model. The SIRS model describes the spread of the disease in a predator population subdivided into susceptible, infected and removed individuals. The Lotka-Volterra model describes the predator-prey interactions. We consider two time scales, a fast one for the disease and a comparatively slow one for predator-prey interactions and for predator mortality. We use the classical “aggregation method” in order to obtain a reduced equivalent model. We show that there are two possible asymptotic behaviors: either the predator population dies out and the prey tends to its carrying capacity, or the predator and prey coexist. In this latter case, the predator population tends either to a “disease-free” or to a “disease-endemic” state. Moreover, the total predator density in the disease-endemic state is greater than the predator density in the “disease-free” equilibrium (DFE).     

热蛋白质组学分析：一种全面评估蛋白质状态的技术

热蛋白质组学分析（thermal proteome profiling,TPP）是细胞热漂移测定（cellular thermal shift assay,CETSA）与定量质谱（quantitative mass spectrometry,MS）的结合,所以也称为MS-CETSA。热蛋白质组学分析通过测量不同加热温度下细胞或细胞裂解物中可溶蛋白的含量来确定整个蛋白质组的稳定性。蛋白质可以在与药物或代谢物等小分子、核酸或其他蛋白质相互作用或在翻译后修饰时改变其热稳定性,而热蛋白质组学分析可以根据有无配体结合蛋白质的热稳定性差异来确定靶蛋白。目前热蛋白质组学分析已成功应用于识别药物的靶点和脱靶点,探究蛋白质-代谢物和蛋白质-蛋白质的相互作用。总体上,国内对这个技术的了解仍然欠缺,对此,文中对热蛋白质组学分析的原理、方法、应用以及优势与局限性进行了综述。     

A Study of the Work of a Medical Social Worker in a Group Medical Practice

An exploratory study was made to demonstrate the role, the work and the relationships of a full-time medical social worker in a group medical practice. Patients were seen on referral only, and a schedule for interview was developed for purposes of categorizing areas of social dysfunction. The following areas of dysfunction were studied: accommodation, job, social activities, family problems and medical diagnosis and/or treatment. A profile emerged of the patients referred as compared to patients in the practice as a whole. The “social sickness” in patients was more likely to exist between the ages of 20 and 44 years or over 65. It occurred more frequently in females and in individuals living alone or in a family of seven or more, in people from the lower social classes and the unemployed, retired people or actual or potential social isolates, those having a psychological illness, and those with degenerative disease of the circulatory or central nervous systems. It was less frequent in patients from a farm.     

Couple-stress moduli of a trabecular bone idealized as a 3D periodic cellular network

Trabecular bone is modeled as a cellular material with an idealized periodic structure made of open cubic cells, which is effectively orthotropic. We evaluate apparent couple-stress moduli of such a periodic material; apparent moduli refer to the moduli obtained using a domain smaller than a Representative Volume Element and they depend on boundary conditions. We conduct this analysis computationally (using ANSYS) by subjecting a unit cell of this periodic cellular material to either displacement or traction boundary conditions. Cell walls, representing bone tissue, and void space, representing bone marrow, are both modeled and they are assumed to be linear elastic. The applied loadings include a uniaxial extension (or uniaxial stress), a hydrostatic deformation (or hydrostatic stress) and a shear deformation (or shear stress) to evaluate the first stiffness (or compliance) tensor, and an applied curvature (or bending moment), a uniaxial twist (or torsion), and a triaxial twist (or triaxial torsion) to evaluate the second couple-stress stiffness (or compliance) tensor. Apparent couple-stress moduli are computed by equating the total strain energy stored in the unit cell with the energy of an equivalent homogeneous orthotropic couple-stress material for each applied loading. The moduli computed using displacement boundary conditions give upper bound, while those obtained using traction boundary conditions give lower bound on effective couple-stress moduli. These bounds are very wide due to a large mismatch in elastic moduli of bone tissue and bone marrow. These results are in agreement with our studies on composite materials with very stiff or very compliant inclusions.     

Neither a mentalist nor a reductionist be!

There is basis for concern that applied psychophysiology, if not the field of biofeedback, is being coopted by, and merged into, a reborn "inner" model, with the return of "cognition" to preeminence in the "psych" and "neuro" disciplines. Despite currently fashionable views that such mentalistic inventions and neuro/psychological developments somehow illuminate behavior or offer simpler accounts of behavioral facts, there is little or no evidence that any such construction has ever told us anything new about behavior.