Surface coat transformation and capsule formation by Leuconostoc mesenteroides NCDO 523 in the presence of sucrose.

When Leuconostoc mesenteroides NCDO 523 was grown in MRS browth, electron microscopy of cells fixed in the presence of ruthenium red showed that the cell wall was covered with a thin layer of filamentous material. When MRS-grown cells were resuspended in the same medium supplemented with 3.6% sucrose, this surface coat doubled in thickness and a number of radial thickenings appeared within it. After 3 h, the filamentous component of the surface coat had disappeared leaving only the radial projections. The progressive accumulation of polymer to produce a capsule visible by light microscopy was observed in only about 20% of the population. In this minority of cells, a dense globular dextran composed of fibrillar and particulate elements was always produced in the initial stages of synthesis. After 18 h, the dextran capsule was generally composed of an inner globular and outer fibrillar layer. It appeared that the outer layer was derived from the globular dextran of the capsule by a process of dispersion.