ABSTRACT
Cable bacteria are long, multicellular micro-organisms that are capable of transporting electrons from cell to cell along the longitudinal axis of their centimeter-long filaments. The conductive structures that mediate this long-distance electron transport are thought to be located in the cell envelope. Therefore, this study examines in detail the architecture of the cell envelope of cable bacterium filaments by combining different sample preparation methods (chemical fixation, resin-embedding, and cryo-fixation) with a portfolio of imaging techniques (scanning electron microscopy, transmission electron microscopy and tomography, focused ion beam scanning electron microscopy, and atomic force microscopy). We systematically imaged intact filaments with varying diameters. In addition, we investigated the periplasmic fiber sheath that remains after the cytoplasm and membranes were removed by chemical extraction. Based on these investigations, we present a quantitative structural model of a cable bacterium. Cable bacteria build their cell envelope by a parallel concatenation of ridge compartments that have a standard size. Larger diameter filaments simply incorporate more parallel ridge compartments. Each ridge compartment contains a ~50 nm diameter fiber in the periplasmic space. These fibers are continuous across cell-to-cell junctions, which display a conspicuous cartwheel structure that is likely made by invaginations of the outer cell membrane around the periplasmic fibers. The continuity of the periplasmic fibers across cells makes them a prime candidate for the sought-after electron conducting structure in cable bacteria.
ABSTRACT
Information about muscular tissue flow is important for diagnosing, treating and monitoring patients with tissue ischemia. For this purpose an objective method which is reproducible and continuous is needed. In co-operation with the company Unisense A/S, we have developed a sensor for instantaneous and continuous monitoring of muscle tissue flow in vivo. The method is based on a flexible microsensor which emits and measures minute amounts of inert tracer gases. The objective was to evaluate the capability of the microsensor to measure varying degrees of tissue flow changes and compare these measurements with the 133Xenon Washout Technique for measuring local perfusion rates in skeletal muscle. The Unisense microsensor was tested in the gracilis muscle of six anaesthetized pigs subjected to varying degrees of muscle ischemia. We found that both tissue flow and pO2 declined in synchrony with reduced blood flow to the lower extremities. All the data from the Unisense microsensor show the same trend as the Xenon data and thus confirms that the microsensor can measure changes in tissue flow.
