Specific Staining for Electron Microscopy of Murein Sacculi of Bacterial Cell Walls

This is the authors' abstract. We don't add key points for this paper.

The murein sacculi of the cell walls of Spirillum serpens consist of a two‐dimensional network of polysaccharide chains covalently connected with oligopeptides. Each oligopeptide in the murein sacculi is a stainable locus which reacts with one heavy atom compound by addition of a stoichiometric amount of the staining agent to a sacculi suspension. The single free amino groups of the oligopeptides are specifically stained by stoichiometric amounts of the heavy atom compounds 3‐hydroxy‐mercuri‐4‐hydroxy‐5‐carboxy‐benzenesulfonic acid, anhydro‐3‐hydroxymercuri‐4‐toluene‐sulfonic acid, Zeise's salt, platinum blue and tri‐bromoacetaldehyde. In a two‐step staining reaction sulfur compounds are bound to the free amino‐ or carboxyl groups of the oligopeptides by reaction with propylenesulfide, N‐acetyl‐DL‐homocysteine‐thio‐lactone and S‐acetylmercaptosuccinic anhydride. These sulfur atoms then react specifically with stoichiometric amounts of 2,4,6‐tris‐acetoxymercuri‐3‐acetaminotoluene. Stained and unstained murein sacculi are observed by high resolution electron microscopy. Unstained murein sacculi can hardly the recognized in bright field and do not expose any structural details. Sacculi specifically stained show distinct contrast and reveal a network pattern in which the stain is localized as discrete particles of about 5 Å diameter in periods of about 10 Å.