Matthias Theves

• Universität Potsdam

The natural habitat of many bacterial swimmers is dominated by interfaces and narrow interstitial spacings where they frequently interact with the fluid boundaries in their vicinity. To quantify these interactions, we investigated the swimming behavior of the soil bacterium Pseudomonas putida in a variety of confined environments. Using microfluidi...

We used microfluidic tools and high-speed time-lapse microscopy to record trajectories of the soil bacterium Pseudomonas putida in a confined environment with cells swimming in close proximity to a glass-liquid interface. While the general swimming pattern is preserved, when compared to swimming in the bulk fluid, our results show that cells in the...

Motile eukaryotic cells, such as leukocytes, cancer cells, and amoeba, typically move inside the narrow interstitial spacings of tissue or soil. While most of our knowledge of actin-driven eukaryotic motility was obtained from cells that move on planar open surfaces, recent work has demonstrated that confinement can lead to strongly altered motile...

Amoebae explore their environment in a random way, unless external cues like, e.g., nutrients, bias their motion. Even in the absence of cues, however, experimental cell tracks show some degree of persistence. In this paper, we analyzed individual cell tracks in the framework of a linear mixed effects model, where each track is modeled by a fractio...

We recorded large data sets of swimming trajectories of the soil bacterium Pseudomonas putida. Like other prokaryotic swimmers, P. putida exhibits a motion pattern dominated by persistent runs that are interrupted by turning events. An in-depth analysis of their swimming trajectories revealed that the majority of the turning events is characterized...

The chemotaxis of eukaryotic cells depends both on the average concentration of the chemoattractant and on the steepness of its gradient. For the social amoeba Dictyostelium discoideum, we test quantitatively the prediction by Ueda and Shibata [Biophys. J. 93, 11 (2007)] that the efficacy of chemotaxis depends on a single control parameter only, na...

Chemotaxis, the directed motion of a cell toward a chemical source, plays a key role in many essential biological processes. Here, we derive a statistical model that quantitatively describes the chemotactic motion of eukaryotic cells in a chemical gradient. Our model is based on observations of the chemotactic motion of the social ameba Dictyosteli...

Gradient dependence of the stochastic part. Constants , , and retrieved from linear fitting of the stochastic part for different gradients (red: perpendicular, black: parallel). As in Fig. 1D of the main text, the data point displayed at very low gradient values (nM/m) corresponds to an experiment where no gradient of cAMP was applied. (TIFF)

Stochastic part of subpopulations. Constants , , and retrieved from linear fitting of the stochastic parts of different subpopulations. (TIFF)

Stochastic components of the Langevin equation. Stochastic component of parallel acceleration, for (a) and (b) . (c) Stochastic component of parallel acceleration, averaged over all angles. Black dots show the experimental data, the red line shows a linear fit . (TIFF)

Directional dependence of the friction coefficient. The friction coefficient is shown as a function of . It is independent of the cell’s direction with respect to the gradient. (TIFF)

Conditional averaging for the non-directional case. Left: The parallel acceleration (red datapoints) can be fitted by a quadratic term (red line) while the perpendicular acceleration is zero and independent of the velocity (green datapoints and constant fit). Right: The stochastic components in the parallel (red) and perpendicular direction (green)...

Testing the influence of cell position in the chamber. Scatter plot displaying each cell according to its mean speed and chemotactic index as a dot in the (,CI)-plane. Black dots denote cells in the lower half of the microfluidic device (i.e., lower half of the gradient), red dots mark cells in the upper half. On average, the black cells move faste...

Effective force term . To establish a relation between the amplitudes and of the angle dependent contributions, we display as a function of . It can be seen that, demonstrating that . (TIFF)

Noise perpendicular to the direction of motion. (A) Stochastic component of the perpendicular acceleration. Black dots show the experimental data, the red lines show a linear fit (B, C) and do not depend on . The red lines show constant fits. (TIFF)

Testing the influence of flow forces. Histograms of the velocity components in x- and y-direction in absence of a chemoattractant gradient (the x-direction corresponding to the direction of fluid flow). Both histograms superpose closely, indicating that the fluid flow does not induce any preferred direction of cell motion. (TIFF)

Many essential functions in eukaryotic cells like phagocytosis, division, and motility rely on the dynamical properties of the actin cytoskeleton. A central player in the actin system is the Arp2/3 complex. Its activity is controlled by members of the WASP (Wiskott-Aldrich syndrome protein) family. In this work, we investigated the effect of the ca...

We used microfluidic tools to expose Dictyostelium discoideum to stationary spatial gradients of the chemoattractant cyclic adenosine 3',5' monophosphate (cAMP). At a cAMP gradient of 10-2 nM/mum, the chemotactic velocity reached a plateau, which continued for gradients up to 1 nM/mum. Our measurements agree with [Song at al, Eur. J. Cell Biol., 85...