Curved Tails in Polymerization-Based Bacterial Motility

The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a visually striking signature of actin polymerization-based motility. Similar actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae, the Vaccinia virus, and vesicles and microspheres in related in vitro systems. We show that the torque required to produce the curvature in the tail can arise from randomly placed actin filaments pushing the bacterium or particle. We find that the curvature magnitude determines the number of actively pushing filaments, independent of viscosity and of the molecular details of force generation. The variation of the curvature with time can be used to infer the dynamics of actin filaments at the bacterial surface.Comment: 8 pages, 2 figures, Latex2

Voronoi Tessellation Captures Very Early Clustering of Single Primary Cells as Induced by Interactions in Nascent Biofilms

Biofilms dominate microbial life in numerous aquatic ecosystems, and in engineered and medical systems, as well. The formation of biofilms is initiated by single primary cells colonizing surfaces from the bulk liquid. The next steps from primary cells towards the first cell clusters as the initial step of biofilm formation remain relatively poorly studied. Clonal growth and random migration of primary cells are traditionally considered as the dominant processes leading to organized microcolonies in laboratory grown monocultures. Using Voronoi tessellation, we show that the spatial distribution of primary cells colonizing initially sterile surfaces from natural streamwater community deviates from uniform randomness already during the very early colonisation. The deviation from uniform randomness increased with colonisation — despite the absence of cell reproduction — and was even more pronounced when the flow of water above biofilms was multidirectional and shear stress elevated. We propose a simple mechanistic model that captures interactions, such as cell-to-cell signalling or chemical surface conditioning, to simulate the observed distribution patterns. Model predictions match empirical observations reasonably well, highlighting the role of biotic interactions even already during very early biofilm formation despite few and distant cells. The transition from single primary cells to clustering accelerated by biotic interactions rather than by reproduction may be particularly advantageous in harsh environments — the rule rather than the exception outside the laboratory

Sustainability Analysis of Personal Transportation for Near Urban Commuting

The goal of this P3 project was to test three hypotheses: 1) there exists a vehicle or class of vehicles that can be effectively used to replace a car for near-urban commuting and short range transportation in cities of similar population, topology and traffic volume as Knoxville, TN with significantly less environmental impact than a typical automobile, 2) this vehicle has the appropriate capacity, convenience, and comfort such that people who are not likely to use other forms of alternate transportation will adopt it, and 3) between a fuel cell hybrid and fully battery electric, one of the two designs will prove to be more effective at satisfying our criteria for low environmental impact with appropriate capacity, convenience, and comfort. A three-wheeled plug-in battery electric vehicle (BEV) was constructed and comprehensively road tested. The fuel cell hybrid equivalent was designed and is currently awaiting installation of an appropriate fuel cell. The overall sustainability of these two vehicles (BugE® BEV and BugE® H2) is compared to that of the best selling passenger car, the Toyota Camry, and a smart fortwo® (intentional non-capitalization). This study analyzes the environmental, social, and economic sustainability of the four vehicles, and was conducted to examine the sustainability of the typical commuting options used for individuals currently commuting in near-urban environments as single passengers in an average passenger car. A public survey of consumer vehicle preferences was created and distributed. We defined “near- urban” as a driving distance of less than 15 miles, one way. Also, these near-urban commuters must have available to them an appropriate route that does not require interstate travel (meaning: a route exists with posted speeds 45 mph or less) although the commuter may currently use the interstate to commute