Electron microscopic study of membranes and walls of bacteria and changes occurring during growth initiation

Abstract

Thin sections of stationary-phase Streptococcus lactis cells showed that the wall and membrane are 20 and 7 nm thick, respectively. Whole cells were examined by negative staining with ammonium molybdate and by shadowing. On air-drying of whole cells, the membrane pulled away from the wall revealing adhesions between these organelles. Adhesions could not be seen after subculture of the stationary-phase cells into complex media or into solutions containing glucose, KCl, and CaCl(2) in tris(hydroxymethyl)aminomethane buffer. The adhesions were also observed in stationary-phase cells of other gram-positive bacteria. Fractured freeze-etched cells of S. lactis had a smooth outside surface, but the inside of the wall (or outside of the membrane) had a regular structure, repeating at 10 nm, which could correspond to the adhesions observed in the negatively stained air-dried cells. Freeze-etching also revealed holes in the outside wall which had the shape of inverted truncated cones. The outside diameter of the cone was 60 nm, and the diameter on the inside surface of the wall was 20 nm. The membrane had upstanding plugs, 20 nm in diameter, which could fill the holes in the wall.