The pigment ofPseudomonas paucimobilis is a carotenoid (Nostoxanthin), rather than a brominated aryl-polyene (xanthomonadin)

Metal ions and their hydroxide or oxide hydrate derivatives interact with the complex polyanionic network of the cell wall and this has drastic effects on the dimensions of the structure. The measured thickness of the wall ofBacillus subtilis (strain Marburg 168) ranged from 16 to 30 nm according to the metal salt used to give contrast. The reactivity of the wall was modified by blocking or altering available reactive groups—e.g., amine, hydroxyl, and carboxyl—and by varying the fixative used. The most significant dimensional changes involved carboxyl modification. The best reference preparations for judging thickness were considered to be replicas of freeze-cleaved and etched specimens, which gave a minimum thickness of 27 nm.