25,629 research outputs found
Overview of mathematical approaches used to model bacterial chemotaxis II: bacterial populations
We review the application of mathematical modeling to understanding the behavior of populations of chemotactic bacteria. The application of continuum mathematical models, in particular generalized Keller–Segel models, is discussed along with attempts to incorporate the microscale (individual) behavior on the macroscale, modeling the interaction between different species of bacteria, the interaction of bacteria with their environment, and methods used to obtain experimentally verified parameter values. We allude briefly to the role of modeling pattern formation in understanding collective behavior within bacterial populations. Various aspects of each model are discussed and areas for possible future research are postulated
A mass-structured individual-based model of the chemostat: convergence and simulation
We propose a model of chemostat where the bacterial population is
individually-based, each bacterium is explicitly represented and has a mass
evolving continuously over time. The substrate concentration is represented as
a conventional ordinary differential equation. These two components are coupled
with the bacterial consumption. Mechanisms acting on the bacteria are
explicitly described (growth, division and up-take). Bacteria interact via
consumption. We set the exact Monte Carlo simulation algorithm of this model
and its mathematical representation as a stochastic process. We prove the
convergence of this process to the solution of an integro-differential equation
when the population size tends to infinity. Finally, we propose several
numerical simulations
Simultaneous growth of two cancer cell lines evidences variability in growth rates
Cancer cells co-cultured in vitro reveal unexpected differential growth rates
that classical exponential growth models cannot account for. Two
non-interacting cell lines were grown in the same culture, and counts of each
species were recorded at periodic times. The relative growth of population
ratios was found to depend on the initial proportion, in contradiction with the
traditional exponential growth model. The proposed explanation is the
variability of growth rates for clones inside the same cell line. This leads to
a log-quadratic growth model that provides both a theoretical explanation to
the phenomenon that was observed, and a better fit to our growth data
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Listeria monocytogenes cell-to-cell spread in epithelia is heterogeneous and dominated by rare pioneer bacteria.
Listeria monocytogenes hijacks host actin to promote its intracellular motility and intercellular spread. While L. monocytogenes virulence hinges on cell-to-cell spread, little is known about the dynamics of bacterial spread in epithelia at a population level. Here, we use live microscopy and statistical modeling to demonstrate that L. monocytogenes cell-to-cell spread proceeds anisotropically in an epithelial monolayer in culture. We show that boundaries of infection foci are irregular and dominated by rare pioneer bacteria that spread farther than the rest. We extend our quantitative model for bacterial spread to show that heterogeneous spreading behavior can improve the chances of creating a persistent L. monocytogenes infection in an actively extruding epithelium. Thus, our results indicate that L. monocytogenes cell-to-cell spread is heterogeneous, and that rare pioneer bacteria determine the frontier of infection foci and may promote bacterial infection persistence in dynamic epithelia. Editorial note:This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter)
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
A stochastic interspecific competition model to predict the behaviour of Listeria monocytogenes in the fermentation process of a traditional Sicilian salami
The present paper discusses the use of modified Lotka-Volterra equations in
order to stochastically simulate the behaviour of Listeria monocytogenes and
Lactic Acid Bacteria (LAB) during the fermentation period (168 h) of a typical
Sicilian salami. For this purpose, the differential equation system is set
considering T, pH and aw as stochastic variables. Each of them is governed by
dynamics that involve a deterministic linear decrease as a function of the time
t and an "additive noise" term which instantaneously mimics the fluctuations of
T, pH and aw. The choice of a suitable parameter accounting for the interaction
of LAB on L. monocytogenes as well as the introduction of appropriate noise
levels allows to match the observed data, both for the mean growth curves and
for the probability distribution of L. monocytogenes concentration at 168 h.Comment: 19 pages, 2 figures, 2 tables. To be published in Eur. Food Res.
Techno
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