265,085 research outputs found
Modelling the Mechanics and Hydrodynamics of Swimming E. coli
The swimming properties of an E. coli-type model bacterium are investigated
by mesoscale hy- drodynamic simulations, combining molecular dynamics
simulations of the bacterium with the multiparticle particle collision dynamics
method for the embedding fluid. The bacterium is com- posed of a
spherocylindrical body with attached helical flagella, built up from discrete
particles for an efficient coupling with the fluid. We measure the hydrodynamic
friction coefficients of the bacterium and find quantitative agreement with
experimental results of swimming E. coli. The flow field of the bacterium shows
a force-dipole-like pattern in the swimming plane and two vor- tices
perpendicular to its swimming direction arising from counterrotation of the
cell body and the flagella. By comparison with the flow field of a force dipole
and rotlet dipole, we extract the force- dipole and rotlet-dipole strengths for
the bacterium and find that counterrotation of the cell body and the flagella
is essential for describing the near-field hydrodynamics of the bacterium
Dynamic compartmentalization of bacteria: accurate division in E. coli
Positioning of the midcell division plane within the bacterium E. coli is
controlled by the min system of proteins: MinC, MinD and MinE. These proteins
coherently oscillate from end to end of the bacterium. We present a
reaction--diffusion model describing the diffusion of min proteins along the
bacterium and their transfer between the cytoplasmic membrane and cytoplasm.
Our model spontaneously generates protein oscillations in good agreement with
experiments. We explore the oscillation stability, frequency and wavelength as
a function of protein concentration and bacterial length.Comment: 4 pages, 4 figures, Latex2e, Revtex
Self Trapping of a Single Bacterium in its Own Chemoattractant
Bacteria (e.g. E. Coli) are very sensitive to certain chemoattractants (e.g.
asparate) which they themselves produce. This leads to chemical instabilities
in a uniform population. We discuss here the different case of a single
bacterium, following the general scheme of Brenner, Levitov and Budrene. We
show that in one and two dimensions (in a capillary or in a thin film) the
bacterium can become self-trapped in its cloud of attractant. This should occur
if a certain coupling constant is larger than unity. We then estimate the
reduced diffusion D_eff of the bacterium in the strong coupling limit, and find
D_eff ~ 1/g.Comment: 4 pages, absolutely no figure
Application of luciferase assay for ATP to antimicrobial drug susceptibility
The susceptibility of bacteria, particularly those derived from body fluids, to antimicrobial agents is determined in terms of an ATP index measured by culturing a bacterium in a growth medium. The amount of ATP is assayed in a sample of the cultured bacterium by measuring the amount of luminescent light emitted when the bacterial ATP is reacted with a luciferase-luciferin mixture. The sample of the cultured bacterium is subjected to an antibiotic agent. The amount of bacterial adenosine triphosphate is assayed after treatment with the antibiotic by measuring the luminescent light resulting from the reaction. The ATP index is determined from the values obtained from the assay procedures
The importance of being adhesive
Phytonematodes cause annual crop losses of $100 billion per year. Pasteuria penetrans is a bacterium that has potential to be developed into a biological control agent as an alternative to nematicides. This poster is an overview of a collagen-like gene that is responsible for adhesion of the bacterium to the nematode's cuticle as the first step in the infection process.Non peer reviewedFinal Accepted Versio
Friend and foe: factors influencing the movement of the bacterium Helicobacter pylori along the parasitism-mutualism continuum.
Understanding the transition of bacterial species from commensal to pathogen, or vice versa, is a key application of evolutionary theory to preventative medicine. This requires working knowledge of the molecular interaction between hosts and bacteria, ecological interactions among microbes, spatial variation in bacterial prevalence or host life history, and evolution in response to these factors. However, there are very few systems for which such broad datasets are available. One exception is the gram-negative bacterium, Helicobacter pylori, which infects upwards of 50% of the global human population. This bacterium is associated with a wide breadth of human gastrointestinal disease, including numerous cancers, inflammatory disorders, and pathogenic infections, but is also known to confer fitness benefits to its host both indirectly, through interactions with other pathogens, and directly. Outstanding questions are therefore why, when, and how this bacterium transitions along the parasitism-mutualism continuum. We examine known virulence factors, genetic predispositions of the host, and environmental contributors that impact progression of clinical disease and help define geographical trends in disease incidence. We also highlight the complexity of the interaction and discuss future therapeutic strategies for disease management and public health in light of the longstanding evolutionary history between the bacterium and its human host
Dissipative Shocks behind Bacteria Gliding
Gliding is a means of locomotion on rigid substrates utilized by a number of
bacteria includingmyxobacteria and cyanobacteria. One of the hypotheses
advanced to explain this motility mechanism hinges on the role played by the
slime filaments continuously extruded from gliding bacteria. This paper solves
in full a non-linear mechanical theory that treats as dissipative shocks both
the point where the extruded slime filament comes in contact with the
substrate, called the filament's foot, and the pore on the bacterium outer
surface from where the filament is ejected. We prove that kinematic
compatibility for shock propagation requires that the bacterium uniform gliding
velocity (relative to the substrate) and the slime ejecting velocity (relative
to the bacterium) must be equal, a coincidence that seems to have already been
observed.Comment: arXiv admin note: text overlap with arXiv:1402.636
Swimming Efficiency of Bacterium Escherichia Coli
We use in vivo measurements of swimming bacteria in an optical trap to
determine fundamental properties of bacterial propulsion. In particular, we
determine the propulsion matrix, which relates the angular velocity of the
flagellum to the torques and forces propelling the bacterium. From the
propulsion matrix dynamical properties such as forces, torques, swimming speed
and power can be obtained from measurements of the angular velocity of the
motor. We find significant heterogeneities among different individuals even
though all bacteria started from a single colony. The propulsive efficiency,
defined as the ratio of the propulsive power output to the rotary power input
provided by the motors, is found to be 0.2%.Comment: 6 page
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