A mathematical model of biofilm growth and spread within plant xylem: Case study of Xylella fastidiosa in olive trees.

Xylem-limited bacterial pathogens cause some of the most destructive plant diseases. Though imposed measures to control these pathogens are generally ineffective, even among susceptible taxa, some hosts can limit bacterial loads and symptom expression. Mechanisms by which this resistance is achieved are poorly understood. In particular, it is still unknown how differences in vascular structure may influence biofilm growth and spread within a host. To address this, we developed a novel theoretical framework to describe biofilm behaviour within xylem vessels, adopting a polymer-based modelling approach. We then parameterised the model to investigate the relevance of xylem vessel diameters on Xylella fastidiosa resistance among olive cultivars. The functionality of all vessels was severely reduced under infection, with hydraulic flow reductions of 2-3 orders of magnitude. However, results suggest wider vessels act as biofilm incubators; allowing biofilms to develop over a long time while still transporting them through the vasculature. By contrast, thinner vessels become blocked much earlier, limiting biofilm spread. Using experimental data on vessel diameter distributions, we were able to determine that a mechanism of resistance in the olive cultivar Leccino is a relatively low abundance of the widest vessels, limiting X. fastidiosa spread.

A 3D image-based modelling approach for understanding spatiotemporal processes in phosphorus fertiliser dissolution, soil buffering and uptake by plant roots.

Phosphorus (P) is a key yield-limiting nutrient for crops, but the main source of P fertiliser is finite. Therefore, efficient fertilisation is crucial. Optimal P application requires understanding of the dynamic processes affecting P availability to plants, including fertiliser dissolution rate and soil buffer power. However, standard soil testing methods sample at fixed time points, preventing a mechanistic understanding of P uptake variability. We used image-based modelling to investigate the effects of fertiliser dissolution rate and soil buffer power on P uptake by wheat roots imaged using X-ray CT. We modelled uptake based on 1-day, 1-week, and 14-week dissolution of a fixed quantity of total P for two common soil buffer powers. We found rapid fertiliser dissolution increased short-term root uptake, but total uptake from 1-week matched 1-day dissolution. We quantified the large effects root system architecture had on P uptake, finding that there were trade-offs between total P uptake and uptake per unit root length, representing a carbon investment/phosphorus uptake balance. These results provide a starting point for predictive modelling of uptake from different P fertilisers in different soils. With the addition of further X-ray CT image datasets and a wider range of conditions, our simulation approach could be developed further for rapid trialling of fertiliser-soil combinations to inform field-scale trials or management.

Precipitation-optimised targeting of nitrogen fertilisers in a model maize cropping system.

Typically, half of the nitrogen (N) fertiliser applied to agricultural fields is lost to the wider environment. This inefficiency is driven by soil processes such as denitrification, volatilisation, surface run-off and leaching. Rainfall plays an important role in regulating these processes, ultimately governing when and where N fertiliser moves in soil and its susceptibility to gaseous loss. The interaction between rainfall, plant N uptake and N losses, however, remains poorly understood. In this study we use numerical modelling to predict the optimal N fertilisation strategy with respect to rainfall patterns and offer mechanistic explanations to the resultant differences in optimal times of fertiliser application. We developed a modelling framework that describes water and N transport in soil over a growing season and assesses nitrogen use efficiency (NUE) of split fertilisations within the context of different rainfall patterns. We used ninety rainfall patterns to determine their impact on optimal N fertilisation times. We considered the effects of root growth, root N uptake, microbial transformation of N and the effect of soil water saturation and flow on N movement in the soil profile. On average, we show that weather-optimised fertilisation strategies could improve crop N uptake by 20% compared to the mean uptake. In drier years, weather-optimising N applications improved the efficiency of crop N recovery by 35%. Further analysis shows that maximum plant N uptake is greatest under drier conditions due to reduced leaching, but it is harder to find the maximum due to low N mobility. The model could capture contrasting trends in NUE seen in previous arable cropping field trials. Furthermore, the model predicted that the variability in NUE seen in the field could be associated with precipitation-driven differences in N leaching and mobility. In conclusion, our results show that NUE in cropping systems could be significantly enhanced by synchronising fertiliser timings with both crop N demand and local weather patterns.

Image-based quantification of soil microbial dead zones induced by nitrogen fertilization.

Microbial communities in agricultural soils underpin many ecosystem services including the maintenance of soil structure, food production, water purification and carbon storage. However, the impact of fertilization on the health of microbial communities is not well understood. This study investigates the spatial and temporal dynamics of nitrogen (N) transport away from a fertilizer granule with pore scale resolution. Specifically, we examined how soil structure and moisture content influence fertilizer derived N movement through the soil pore network and the subsequent impact of on soil microbial communities. We develop a mathematical model to describe N transport and reactions in soil at the pore-scale. Using X-ray Computed Tomography scans, we reconstructed a microscale description of a soil-pore geometry as a computational mesh. Solving two-phase water/air model produced pore-scale water distributions at 15, 30 and 70% water-filled pore volume. The N-speciation model considered ammonium (NH4+), nitrate (NO3-) and dissolved organic N (DON), and included N immobilization, ammonification and nitrification processes, as well as diffusion in soil solution. We simulated the dissolution of a fertilizer pellet and a pore scale N cycle at three different water saturations. To aid interpretation of the model results, microbial activity at a range of N concentrations was measured. The model showed that the diffusion and concentration of N in water films is critically dependent upon soil moisture and N species. We predict that the maximum NH4+ and NO3- concentrations in soil solution around the pellet under dry conditions are in the order of 1 × 103 and 1 × 104 mol m-3 respectively, and under wet conditions 2 × 102 and 1 × 103 mol m-3, respectively. Supporting experimental evidence suggests that these concentrations would be sufficient to reduce microbial activity in the short-term in the zone immediately around the fertilizer pellet (ranging from 0.9 to 3.8 mm), causing a major loss of soil biological functioning. This model demonstrates the importance of pore-scale processes in regulating N movement and their interactions with the soil microbiome.

[Associated risk factors for infection in open fractures by firearms]. / Factores de riesgo asociados a infección de fracturas expuestas por proyectil de arma de fuego.

BACKGROUND: The introduction of firearms has increased deaths, assassinations and suicides. Firearm projectile injuries (PAF) increasingly affect civilian populations (500,000 injuries annually), it is the second cause of death in young people. Half required fracture treatment (45%), accompanied by reports of 6% who developed a deep infection. MATERIAL AND METHODS: Retrospective, observational, cross-sectional study in four hospitals of the Secretary of Health of CDMX of the frequency of infection in fractures exposed by PAF and if there is any other factor that is associated with the infection. RESULTS: In the review of the files of the four hospitals, 67 patients were found, men, with an incidence of infections of 4.5%, when analyzing the risk factors these did not present a significant association. DISCUSSION: No risk factor has statistical significance for any infectious process to occur, probably due to a good initial treatment.

ANTECEDENTES: La introducción de armas de fuego ha incrementado las muertes, asesinatos y suicidios. Las lesiones por proyectil de arma de fuego (PAF) afectan cada vez más a poblaciones civiles (500,000 lesiones anualmente) y es la segunda causa de muerte en jóvenes. La mitad requiere tratamiento de fracturas (45%), acompañado de reportes de 6% que desarrollaron una infección profunda. MATERIAL Y MÉTODOS: Estudio retrospectivo, observacional y transversal en cuatro hospitales de la Secretaría de Salud de la CDMX de la frecuencia de infección en fracturas expuestas por PAF y si existe algún otro factor que acompañe a la infección. RESULTADOS: Se encontraron en la revisión de los expedientes de los cuatro hospitales a 67 pacientes, hombres, con una incidencia de infecciones de 4.5%, al analizar los factores de riesgo éstos no presentaron asociación significativa. DISCUSIÓN: Ningún factor de riesgo posee significancia estadística de que se presente algún proceso infeccioso, probablemente por un buen tratamiento inicial.

The unidirectional valve is the best method to determine maximal inspiratory pressure during weaning.

OBJECTIVES: Although maximal inspiratory pressure (MIP) is used as an index of inspiratory muscular strength, there is no consensus on how to measure it. We compared, during weaning from mechanical ventilation, two methods of measurement to determine which shows the greater values (MIPbest) and is more reproducible. One method measured MIP when negative pressure was maintained for at least 1 s after a forceful expiration, and the other method measured MIP with a unidirectional expiratory valve (MIPuni). DESIGN: The study had a crossover design, and patients randomly performed three measurements of each method (t1). The procedure was repeated by the same observer after 20 min (t2). The maximal value in each method was considered. SETTING: ICU, Hospital A.C. Camargo, São Paulo, Brazil. PATIENTS: Fifty-four consecutive patients undergoing short-term mechanical ventilation who became eligible for the study when their physicians decided to restore spontaneous breathing. RESULTS: MIPbest values were arrived at using MIPuni 75% of the time either in tl or t2. MIPuni yielded a higher average of MIPbest values in t1 and t2 (p < 0.0001). The effort-to-effort coefficient of variation of one method compared with the other during t1 and t2 was similar (p > 0.2 for t1; p > 0.8 for t2). Also, when comparing tl and t2, the coefficients of variation were similar for each method (p > 0.62). CONCLUSIONS: Because MIPuni displayed the maximal values, it is the best method for estimating MIP in patients undergoing short-term mechanical ventilation. The reproducibility of consecutive measurements was similar between the methods, even after a short period of time.

An unusual niche for an opportunistic fungus.

An acrylic on canvas painting from the collection of the Institute of Puerto Rico Culture was found to be stained with light brown spots. Under ultraviolet light it was evident that these spots covered the entire painting. Scotch tape samples from different areas of the painting were taken. In almost all of these samples, septated hyphae were observed to surround the canvas fibers and in most of them, spiny or rough-surfaced conidia were also observed. A sample from the canvas which was incubated over a Sabourand agar plate yielded a fungus very similar to the one observed in the tape samples after subculturing in potato dextrose agar. Slide cultures and culture characteristics provided evidence that this fungus was a species of Scopulariopsis. This fungus has been implicated in human disease and in this case, it was the cause of the deterioration of the painting.

Shape anisotropy of a single random-walk polymer.

Random walks have been used to describe a wide variety of systems ranging from cell colonies to polymers. Sixty-five years ago, Kuhn [Kuhn, W. (1934) Kolloid-Z. 68, 2-11] made the prediction, backed later by computer simulations, that the overall shape of a random-walk polymer is aspherical, yet no experimental work has directly tested Kuhn's general idea and subsequent computer simulations. By using fluorescence microscopy, we monitored the conformation of individual, long, random-walk polymers (fluorescently labeled DNA molecules) at equilibrium. We found that a polymer most frequently adopts highly extended, nonfractal structures with a strongly anisotropic shape. The ensemble-average ratio of the lengths of the long and short axes of the best-fit ellipse of the polymer was much larger than unity.

Receptive-field properties and morphological characteristics of the superior collicular neurons that project to the lateral posterior and dorsal lateral geniculate nuclei in the hamster.

1. Intracellular recording, antidromic activation, and horseradish peroxidase (HRP) injection techniques were employed to characterize the receptive-field properties and morphology of the superior collicular (SC) neurons in the hamster that projected to the lateral posterior nucleus (LP) or the dorsal lateral geniculate body (LGNd). 2. Twenty-three tecto-LP and 21 tecto-LGNd cells were successfully characterized, filled with HRP, and recovered. Additional physiological information was obtained from four tecto-LP and five tecto-LGNd neurons in which HRP injections did not completely label the cell, but did provide information as to the laminar location of the soma. Recovered neurons were classified as wide-field or narrow-field vertical cells, marginal cells, stellate cells, or horizontal cells on the basis of their soma-dendritic morphology. They were categorized as stationary responsive (SR), movement sensitive (MV), or directionally selective (DS) on the basis of their physiological responses (3, 37). 3. The somas of the recovered tecto-LP cells were located, with two exceptions, in, or near, the borders of the stratum opticum (SO). Tecto-LGNd neurons, with two exceptions, had their cell bodies in the upper one-half of the stratum griseum superficiale (SGS). Fifty-two percent of the recovered tecto-LP cells were wide-field vertical cells, 22% were narrow-field vertical cells, 13% were stellate cells, 9% were horizontal cells, and 4% could not be classified according to the scheme that we employed. Twenty-four percent of the recovered tecto-LGNd cells were marginal cells, 24% were stellate cells, 38% were narrow-field vertical cells, 5% were horizontal cells, 5% were wide-field vertical cells, and 5% could not be classified. The difference between the distributions of morphological cell types that contributed to the tecto-LGNd and tecto-LP pathways was statistically significant (chi 2 = 15.8, P less than 0.01). 4. Sixty-seven percent of the tecto-LP cells had MV receptive fields, 11% were DS, 7% had SR fields, and 15% were unresponsive. The distribution of receptive-field types for tecto-LGNd cells was somewhat different: 54% had SR fields, 15% were MV, 19% were DS, 4% were somatosensory, 4% were unresponsive, and 4% were incompletely classified. These differences between tecto-LP and tecto-LGNd cells were statistically significant (chi 2 = 18.4, P less than 0.001). The strongest correlation between morphology and receptive-field type was observed for the wide-field vertical cells that projected to LP. All but one of these had MV receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)