How to connect time-lapse recorded trajectories of motile microorganisms with dynamical models in continuous time

We provide a tool for data-driven modeling of motility, data being time-lapse recorded trajectories. Several mathematical properties of a model to be found can be gleaned from appropriate model-independent experimental statistics, if one understands how such statistics are distorted by the finite sampling frequency of time-lapse recording, by experimental errors on recorded positions, and by conditional averaging. We give exact analytical expressions for these effects in the simplest possible model for persistent random motion, the Ornstein-Uhlenbeck process. Then we describe those aspects of these effects that are valid for any reasonable model for persistent random motion. Our findings are illustrated with experimental data and Monte Carlo simulations.

Assessment of automated analyses of cell migration on flat and nanostructured surfaces

Motility studies of cells often rely on computer software that analyzes time-lapse recorded movies and establishes cell trajectories fully automatically. This raises the question of reproducibility of results, since different programs could yield significantly different results of such automated analysis. The fact that the segmentation routines of such programs are often challenged by nanostructured surfaces makes the question more pertinent. Here we illustrate how it is possible to track cells on bright field microscopy images with image analysis routines implemented in an open-source cell tracking program, PACT (Program for Automated Cell Tracking). We compare the automated motility analysis of three cell tracking programs, PACT, Autozell, and TLA, using the same movies as input for all three programs. We find that different programs track overlapping, but different subsets of cells due to different segmentation methods. Unfortunately, population averages based on such different cell populations, differ significantly in some cases. Thus, results obtained with one software package are not necessarily reproducible by other software.

Cell motility, morphology, viability and proliferation in response to nanotopography on silicon black

Knowledge of cells' interactions with nanostructured materials is fundamental for bio-nanotechnology. We present results for how individual mouse fibroblasts from cell line NIH3T3 respond to highly spiked surfaces of silicon black that were fabricated by maskless reactive ion etching (RIE). We did standard measurements of cell viability, proliferation, and morphology on various surfaces. We also analyzed the motility of cells on the same surfaces, as recorded in time lapse movies of sparsely populated cell cultures. We find that motility and morphology vary strongly with nano-patterns, while viability and proliferation show little dependence on substrate type. We conclude that motility analysis can show a wide range of cell responses e.g. over a factor of two in cell speed to different nano-topographies, where standard assays, such as viability or proliferation, in the tested cases show much less variation of the order 10-20%.

Spectroscopy and reactivity of a photogenerated tryptophan radical in a structurally defined protein environment

Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE.