Polysaccharide capsule of Escherichia coli: microscope study of its size, structure, and sites of synthesis

Abstract

This report describes the structure, size, and shape of the uncollapsed polysaccharide capsule of Escherichia coli strain Bi 161/42 [09:K29(A):H-], its ultrastructural preservation as well as the filamentous components of the isolated capsular material. In a temperature-sensitive mutant, sites were localized at which capsular polysaccharide is "exported" to the cell surface. The highly hydrated capsule of the wild-type cells was visible in the uncollapsed state after freeze-etching, whereas dehydration in .50% acetone or alcohol caused the capsule to collapse into thick bundles. This was prevented by pretreatment of the cell with capsule-specific immunoglobulin G; the capsule appeared as a homogeneous layer of 250to 300-nm thickness. The structural preservation depended on the concentration of the anti-capsular immunoglobulin G. Temperature-sensitive mutants, unable to produce capsular antigen at elevated temperatures, showed, 10 to 15 min after shift down to permissive temperature, polysaccharide strands with K29 specificity appearing at the cell surface at roughly 20 sites per cell; concomitantly, capsule-directed antibody started to agglutinate the bacteria. The sites at which the new antigen emerged were found in random distribution over the entire surface of the organism. Spreading ofpurified polysaccharide was achieved on air-water interfaces; after subsequent shadow casting with heavy metal, filamentous elements were observed with a smallest class of filaments measuring 250 nm in length and 3 to 6 nm in width. At one end these fibers revealed a knoblike structure of about 10-nm diameter. The slimelike polysaccharides from mutants produced filamentous bundles of >100-,um length, with antigenic and phage-receptor properties indistinguishable from those of the wild-type K29 capsule antigen.

Effect of fixation‐resin combinations and ruthenium red on elucidating outer envelope structure and surface morphology of two methanotrophic bacteria

“…In comparison, RR Met hod B is the chemical method that most closely resembles the FE preparation in that both of these structures were present. In all other fixations, the appearance of "spikes" is likely an artifact produced either by collapse of the filaments as a dehydration effect (Bayer and Thurow, 1977) or by collapse of the beads from loss of structural integrity and/or modification of molecular bonds.…”

Developmental pathway for biofilm formation in curli‐producing Escherichia coli strains: role of flagella, curli and colanic acid

“…Biofilms were formed on thermanox coverslips as described in Experimental procedures and observations made after 24 h of culture. Dehydratation during specimen preparation for electron microscopy leads to shrinkage of the highly hydrated exopolysaccharide matrix (Bayer and Thurow, 1977;Costerton et al, 1978). CA appears as white pellets of condensed material, and is only present around sessile cells of the mucoid PHL644 (A) and PHL940 (E) strains.…”

Electron Microscopic Observation of Branhamella catarrhalis

“…Capsular polysaccharides are also important surface determinants present on pathogenic gram-negative and gram-positive bacteria (5). The variety of functions in which the bacterial capsule is involved is described elsewhere (1). With emergence of B. catarrhalis as a significant human pathogen, studies on surface structures will be important to understand virulence factors and pathogenesis (10).…”