Electron Microscopy of Salmonella Flagella in Methylcellulose Solution

When peritrichously flagellated cells such as normal, curly, paralysed-curly and small-amplitude strains of Salmonella abortusequi are suspended in 0·5% methylcellulose solution, flagellar bundles can be clearly seen by electron microscopy. In a bundle, five or more of the component flagella are tightly united in parallel with each other, and the bundle formed into a helix with a shape characteristic for each strain. These figures reveal the structural detail of the flagellar bundle observed under a dark-field microscope. Ten minutes after the cells were suspended in methylcellulose solution, bundled flagella could be seen in approximately 70 % of the cells of normal, curly and paralysed-curly strains; the remaining 30 % were dispersed. At this time among the normal cells, some were single-bundled and others were multi-bundled. The fraction of single-bundled cells was larger in both motile and paralysed curly-flagellated cells than in normal cells. The fraction of normal cells having single bundles increased with time. Methylcellulose was therefore presumed to enhance aggregation of flagella and/or to inhibit the dispersion of the aggregated flagella.

In the small-amplitude strain, transformation of flagellar shape to curly has been previously observed. In methylcellulose solution, this transformation occurs in bundled flagella but not in dispersed flagella. It is inferred that the tight association of the component flagella in methylcellulose solution enhances the stress among the flagella, thus causing the transformation.