The use of bioluminescence for monitoring in planta growth dynamics of a Pseudomonas syringae plant pathogen

The use of bioluminescence was evaluated as a tool to study Pseudomonas syringae population dynamics in susceptible and resistant plant environments. Plasmid pGLITE, containing the luxCDABE genes from Photorhabdus luminescens, was introduced into Pseudomonas syringae pv. phaseolicola race 7 strain 1449B, a Gram-negative pathogen of bean (Phaseolus vulgaris). Bacteria recovered from plant tissue over a five-day period were enumerated by counting numbers of colony forming units and by measurement of bioluminescence. Direct measurement of bioluminescence from leaf disc homogenates consistently reflected bacterial growth as determined by viable counting, but also detected subtle effects of the plant resistance response on bacterial viability. This bioluminescence procedure enables real time measurement of bacterial metabolism and population dynamics in planta, obviates the need to carry out labour intensive and time consuming traditional enumeration techniques and provides a sensitive assay for studying plant effects on bacterial cells.

Wheat archive links long-term population dynamics of pathogens to air pollution

We used the PCR to study the presence of two plant pathogens in archived wheat samples from a long-term experiment started in 1843. The data were used to construct a unique 160-yr time-series of the abundance of Phaeosphaeria nodorum and Mycosphaerella graminicola, two important pathogens of wheat. During the period since 1970, the relative abundance of DNA of these two pathogens in the samples has reflected the relative importance of the two wheat diseases they cause in U.K. disease surveys. Unexpectedly, changes in the ratio of the pathogens over the 160-yr period were very strongly correlated with changes in atmospheric pollution, as measured by SO2 emissions. This finding suggests that long-term, economically important, changes in pathogen populations can be influenced by anthropogenically induced environmental changes.

Joint effects of population density and toxicant exposure on population dynamics of Capitella sp I

Very few studies have analyzed the dependence of population growth rate on population density, and even fewer have considered interaction effects of density and other stresses, such as exposure to toxic chemicals. Yet without such studies we cannot know whether chemicals harmful at low density have effects on carrying capacity or, conversely, whether chemicals reducing carrying capacity are also harmful at low density, impeding a population's capacity to recover from disturbance. This study examines the combined effects of population density and a toxicant (fluoranthene) on population growth rate (pgr) and carrying capacity using the deposit-feeding polychaete Capitella sp. I as a test organism. Populations were initiated with a stable age distribution, and population density and age/size distribution were followed during a period of 28 wk. Fluoranthene (FLU), population density, and their interaction influenced population growth rate. Population growth rate declined linearly with the logarithm of population biomass, but the slope of the relationship was steeper for the control populations than for populations exposed to 50 mug FLU/(g sediment dry mass). Populations exposed to 150 mug FLU/(g sediment dry mass) went extinct after 8 wk of exposure. Despite concerns that toxicant effects would be exacerbated at high density, we found the reverse to be the case, and effects of fluoranthene on population growth rate were much reduced in the region of carrying capacity. Fluoranthene did. reduce carrying capacity by 46%, and this could haven important implications for interacting species and/or sediment biogeochemical processes.

The dynamics of threat, fear and intentionality in the conduct disorders: longitudinal findings in the children of women with post-natal depression

This paper considers how environmental threat may contribute to the child's use of avoidant strategies to regulate negative emotions, and how this may interact with high emotional reactivity to create vulnerability to conduct disorder symptoms. We report a study based on the hypothesis that interpreting others' behaviours in terms of their motives and emotions - using the intentional stance - promotes effective social action, but may lead to fear in threatful situations, and that inhibiting the intentional stance may reduce fear but promote conduct disorder symptoms. We assessed 5-year-olds' use of the intentional stance with an intentionality scale, contrasting high and low threat doll play scenarios. In a sample of 47 children of mothers with post-natal depression ( PND) and 35 controls, children rated as securely attached with their mothers at the age of 18 months were better able to preserve the intentional stance than insecure children in high threat scenarios, but not in low threat scenarios. Girls had higher intentionality scores than boys across all scenarios. Only intentionality in the high threat scenario was associated with teacher-rated conduct disorder symptoms, and only in the children of women with PND. Intentionality mediated the associations between attachment security and gender and conduct disorder symptoms in the PND group.

Linking the coevolutionary and population dynamics of host-parasitoid interactions

The interplay between coevolutionary and population or community dynamics is currently the focus of much empirical and theoretical consideration. Here, we develop a simulation model to study the coevolutionary and population dynamics of a hypothetical host-parasitoid interaction. In the model, host resistance and parasitoid virulence are allowed to coevolve. We investigate how trade-offs associated with these traits modify the system's coevolutionary and population dynamics. The most important influence on these dynamics comes from the incorporation of density-dependent costs of resistance ability. We find three main outcomes. First, if the costs of resistance are high, then one or both of the players go extinct. Second, when the costs of resistance are intermediate to low, cycling population and coevolutionary dynamics are found, with slower evolutionary changes observed when the costs of virulence are also low. Third, when the costs associated with resistance and virulence are both high, the hosts trade-off resistance against fecundity and invest little in resistance. However, the parasitoids continue to invest in virulence, leading to stable host and parasitoid population sizes. These results support the hypothesis that costs associated with resistance and virulence will maintain the heritable variation in these traits found in natural populations and that the nature of these trade-offs will greatly influence the population dynamics of the interacting species.

Dynamics of shear-induced orientation transitions in block copolymers

This review discusses liquid crystal phase formation by biopolymers in solution. Lyotropic mesophases have been observed for several classes of biopolymer including DNA, peptides, polymer/peptide conjugates, glycopolymers and proteoglycans. Nematic or chiral nematic (cholesteric) phases are the most commonly observed mesophases, in which the rod-like fibrils have only orientational order. Hexagonal columnar phases are observed for several systems (DNA, PBLG, polymer/peptide hybrids) at higher concentration. Lamellar (smectic) phases are reported less often, although there are examples such as the layer arrangement of amylopectin side chains in starch. Possible explanations for the observed structures are discussed. The biological role of liquid crystal phases for several of these systems is outlined. Commonly, they may serve as a template to align fibrils for defined structural roles when the biopolymer is extruded and dried, for instance in the production of silk by spiders or silkworms, or of chitin in arthropod shells. In other cases, liquid crystal phase formation may occur in vivo simply as a consequence of high concentration, for instance the high packing density of DNA within cell nuclei.

Computer simulations of structures, energetics and dynamics of myoglobin center dot center dot center dot ligand complexes

Myoglobin has been studied in considerable detail using different experimental and computational techniques over the past decades. Recent developments in time-resolved spectroscopy have provided experimental data amenable to detailed atomistic simulations. The main theme of the present review are results on the structures, energetics and dynamics of ligands ( CO, NO) interacting with myoglobin from computer simulations. Modern computational methods including free energy simulations, mixed quantum mechanics/molecular mechanics simulations, and reactive molecular dynamics simulations provide insight into the dynamics of ligand dynamics in confined spaces complementary to experiment. Application of these methods to calculate and understand experimental observations for myoglobin interacting with CO and NO are presented and discussed.

Computational chemistry for elucidating protein function: energetics and dynamics of myoglobin-ligand systems

State-of-the-art computational methodologies are used to investigate the energetics and dynamics of photodissociated CO and NO in myoglobin (Mb···CO and Mb···NO). This includes the combination of molecular dynamics, ab initio MD, free energy sampling, and effective dynamics methods to compare the results with studies using X-ray crystallography and ultrafast spectroscopy metho ds. It is shown that modern simulation techniques along with careful description of the intermolecular interactions can give quantitative agreement with experiments on complex molecular systems. Based on this agreement predictions for as yet uncharacterized species can be made.

Theoretical investigation of infrared spectra and pocket dynamics of photodissociated carbonmonoxy myoglobin

Molecular dynamics simulations of the photodissociated state of carbonmonoxy myoglobin (MbCO) are presented using a fluctuating charge model for CO. A new three-point charge model is fitted to high-level ab initio calculations of the dipole and quadrupole moment functions taken from the literature. The infrared spectrum of the CO molecule in the heme pocket is calculated using the dipole moment time autocorrelation function and shows good agreement with experiment. In particular, the new model reproduces the experimentally observed splitting of the CO absorption spectrum. The splitting of 3–7 cm−1 (compared to the experimental value of 10 cm−1) can be directly attributed to the two possible orientations of CO within the docking site at the edge of the distal heme pocket (the B states), as previously suggested on the basis of experimental femtosecond time-resolved infrared studies. Further information on the time evolution of the position and orientation of the CO molecule is obtained and analyzed. The calculated difference in the free energy between the two possible orientations (Fe···CO and Fe···OC) is 0.3 kcal mol−1 and agrees well with the experimentally estimated value of 0.29 kcal mol−1. A comparison of the new fluctuating charge model with an established fixed charge model reveals some differences that may be critical for the correct prediction of the infrared spectrum and energy barriers. The photodissociation of CO from the myoglobin mutant L29F using the new model shows rapid escape of CO from the distal heme pocket, in good agreement with recent experimental data. The effect of the protein environment on the multipole moments of the CO ligand is investigated and taken into account in a refined model. Molecular dynamics simulations with this refined model are in agreement with the calculations based on the gas-phase model. However, it is demonstrated that even small changes in the electrostatics of CO alter the details of the dynamics.

Dynamics of brand competition: Effects of unobserved social networks

Brand competition is modelled using an agent based approach in order to examine the long run dynamics of market structure and brand characteristics. A repeated game is designed where myopic firms choose strategies based on beliefs about their rivals and consumers. Consumers are heterogeneous and can observe neighbour behaviour through social networks. Although firms do not observe them, the social networks have a significant impact on the emerging market structure. Presence of networks tends to polarize market share and leads to higher volatility in brands. Yet convergence in brand characteristics usually happens whenever the market reaches a steady state. Scale-free networks accentuate the polarization and volatility more than small world or random networks. Unilateral innovations are less frequent under social networks.