Ultrastructure and adhesion properties of Ruminococcus albus

Morphological studies have shown that cells of the anaerobic rumen bacterium Ruminococcus albus have electron-translucent granules of reserve carbohydrate in their cytoplasm, and that they have a polysaccharide "coat" layer external to their gram-negative cell wall. This coat layer, which stains specifically with ruthenium red, forms a compact mat of fibers adjacent to the cell, and fibrous elements also project as much as 0.6 mum from the cells. These radial fibers are clearly visualized by freeze-etching, and can be seen to extend throughout the extensive intercullular space in centrifuged pellets of these bacteria. Cells of R. albus adhere to cellulose fibers added to the culture medium, and the coat material is seen to mediate this adhesion in addition to its function in the general protection of these cells.