[Electron microscopic studies of the insertion of pili in the newly isolated hydrogen-oxidizing bacterium 2K1]

Cells of the hydrogen-oxidizing bacterium 2K1 exhibited numerous pili of varying length, with a diameter of 7--8 nm as measured from negatively stained samples. At the basis of each pilus, a cell wall differentiation was observed appearing, in face-on-view, as a ring-like structure made up of subunits, and in side-on view as a hollow cylinder penetrating through the cell wall. It is assumed that these ring-like structures are in direct relation with the presence of the pili. As the number of ring-like structures per cell was higher than the number of pili per cell, rings without associated pili might either be sites of polymerizing pili, or "dead" pilus channel complexes out of function due to pilus break-down.