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At least 793 records · Page 44Linked to original sources
PubMed1989

Interference reflection microscopic study of sites of association between gliding bacteria and glass substrata.

Sites of close contact between gliding Cytophaga sp. strain U67 cells and glass were examined by interference reflection microscopy. Site patterns changed during translocation and moved relative to the substratum, in contrast to previous interference reflection microscopy observations of fibroblast and amoeboid motility. Sinistral rotation around the long axis of the cell was coupled with gliding, except when curved cells traversed curvilinear pathways. Close contact was temporary, since cells flipped up off the substratum on one pole, pivoted, or were displaced laterally in collisions. Other members of the order Cytophagales and Myxococcus sp. demonstrated similar patterns of close association with substrata.

Bacterial Adhesion↗
PubMed1992

Evanescent interference patterns for fluorescence microscopy.

The increasing experimental use of total internal reflection/fluorescence photobleaching recovery has motivated a theoretical study of the spatial intensity profiles generated by two interfering evanescent waves. The interference patterns generated by evanescent waves differ considerably from those generated by plane waves in a homogenous medium because evanescent waves are not transverse and because the evanescent propagation number depends on the incidence angle of the totally internally reflected light. The periodicity and contrast of the evanescent interference patterns under various conditions are calculated; these parameters depend on the intensities, polarizations, and incidence angles of the two incident beams, as well as the refractive indices of the two media that form the planar interface where total internal reflection occurs. The derived intensity profiles are used to develop expressions for the shapes of fluorescence photobleaching recovery curves when evanescent interference patterns are used for fluorescence excitation and bleaching. The calculations also suggest that colliding beam experiments may confirm theoretically predicted evanescent field polarizations.

Binding Sites↗
PubMed1981

Myoblasts are aligned with collagen fibrils in regenerating frog tadpole tails.

Myoblasts in the regenerating frog tadpole tail differentiate from mesenchymal cells that lie next to the basement membrane of the epidermis of the tail. As these cells elongate and form myotubes, they orientate uniformly in the longitudinal axis of the tail. The collagen fibrils of the basement membrane adjacent to the myogenic cells are also orientated in the tail axis just prior to and during the time when the myogenic cells are elongating. This has been demonstrated by transmission electron microscopy of thin sections, by differential interference contrast microscopy of isolated basement membranes, and by scanning electron microscopy of the inner surface of the basement membrane. Since elongating myoblasts are in contact with the longitudinally orientated fibrils, the latter could provide directional cues to the elongating myoblasts. This proposition is supported by the finding that isolated basement membranes readily orientate cells that are cultured upon their inner surfaces.

Animals↗
PubMed1997

An in vitro method for detecting infectious Cryptosporidium oocysts with cell culture.

Current assay methods to detect Cryptosporidium oocysts in water are generally not able to evaluate viability or infectivity. A method was developed for low-level detection of infective oocysts by using HCT-8 cells in culture as hosts to C. parvum reproductive stages. The infective foci were detected by labeling intracellular developmental stages of the parasite in an indirect-antibody assay with a primary antibody specific for reproductive stages and a secondary fluorescein isothiocyanate-conjugated antibody. The complete assay was named the focus detection method (FDM). The infectious foci (indicating that at least one of the four sporozoites released from a viable oocyst had infected a cell) were enumerated by epifluorescence microscopy and confirmed under Nomarski differential interference contrast microscopy. Time series experiments demonstrated that the autoreinfective life cycle in host HCT-8 cells began after 12 h of incubation. Through dilution studies, levels as low as one infectious oocyst were detected. The cell culture FDM compared well to other viability assays. Vital stains and excystation demonstrated that oocyst populations less than 1% viable (by vital dyes) and having a low sporozoite yield following excystation could not infect host cells. Until now, the water industry has relied on an oocyst detection method (under an information collection regulation) that is unable to determine viability. The quantifiable results of the cell culture method described demonstrate two important applications: (i) an infectivity assay that may be used in conjunction with current U.S. Environmental Protection Agency-mandated detection methodologies, and (ii) a method to evaluate oocyst infectivity in survival and disinfection studies.

Animals↗
PubMed1998

Gas vesicle genes identified in Bacillus megaterium and functional expression in Escherichia coli.

Gas vesicles are intracellular, protein-coated, and hollow organelles found in cyanobacteria and halophilic archaea. They are permeable to ambient gases by diffusion and provide buoyancy, enabling cells to move upwards in liquid to access oxygen and/or light. In halobacteria, gas vesicle production is encoded in a 9-kb cluster of 14 genes (4 of known function). In cyanobacteria, the number of genes involved has not been determined. We now report the cloning and sequence analysis of an 8,142-bp cluster of 15 putative gas vesicle genes (gvp) from Bacillus megaterium VT1660 and their functional expression in Escherichia coli. Evidence includes homologies by sequence analysis to known gas vesicle genes, the buoyancy phenotype of E. coli strains that carry this gvp gene cluster, the presence of pressure-sensitive, refractile bodies in phase-contrast microscopy, structural details in phase-contrast microscopy, structural details in direct interference-contrast microscopy, and shape and size revealed by transmission electron microscopy. In B. megaterium, the gvp region carries a cluster of 15 putative genes arranged in one orientation; they are open reading frame 1 and gvpA, -P, -Q, -B, -R, -N, -F, -G, -L, -S, -K, -J, -T, and -U, of which the last 11 genes, in a 5.7-kb gene cluster, are the maximum required for gas vesicle synthesis and function in E. coli. To our knowledge, this is the first example of a functional gas vesicle gene cluster in nonaquatic bacteria and the first example of the interspecies transfer of genes resulting in the synthesis of a functional organelle.

Amino Acid Sequence↗
PubMed1988

Coiled perimysial fibers of papillary muscle in rat heart: morphology, distribution, and changes in configuration.

The morphology, distribution, and configuration of coiled perimysial fibers of rat heart papillary muscle were studied. Methods included bright-field light microscopy of silver-stained sections, scanning and transmission electron microscopy, and differential interference contrast light microscopy of unfixed and unstained specimens. Coiled fibers, elliptical in cross section, are arranged in a branched network that diverges from the muscle-tendon junction and is continuous throughout the length of the muscle and into the ventricle wall. Most fibers range in diameter from less than 1 micron to 10 micron and are parallel with the long axis of the muscle, although branching is common and oblique orientations are seen. Several myocytes are associated with each coiled perimysial fiber. Constituent fibrils (diameter, 40-50 nm) occur in bundles twisted within the fiber. Small satellite elastic fibers are parallel to the collagen fiber axes. Stereo analysis of the coiled perimysial fibers reveals helical configurations, as opposed to planar waviness, that become less convoluted or even straighten as the resting muscle is stretched. Calculations based on cross-sectional areas of fibers, changes in fiber configurations, and tensile moduli reported for collagen fibers of other tissues show that the potential tensile strength of the network of coiled perimysial fibers is sufficient to contribute significantly to the mechanical properties of papillary muscle. Detailed evaluations of possible roles of the coiled perimysial collagen fiber system as a function of passive stretch and contraction in ventricular wall, as well as in papillary muscle, warrant further study.

Animals↗