Fine structure and isolation of the hook-basal body complex of flagella from Escherichia coli and Bacillus subtilis.

The hook-basal body complex comprising the basal end of purified intact flagella from Escherichia coli and Bacillus subtilis was studied in detail with an electron microscope. The E. coli hook can be described as having five or six concentric helical coils. The basal body from E. coli is 27 nm in length and consists of four rings, 22.5 nm in diameter, arranged in two pairs and mounted on a rod. The top pair of rings is connected near their periphery, resembling a closed cylinder. In B. subtilis the basal body looks like that from E. coli, except that the top pair of rings is missing. Hook-basal body complexes from both organisms could be isolated by dissociating the filaments with either urea or acid. Based on our results, two types of basal body structures are proposed, as exemplified by E. coli and B. subtilis, which directly reflect the structure of the gram-negative and gram-positive cell envelopes.