Hamilton and Chandler examined the ultrastructure of flagellar basal organelles in Clostridium chauvoei using electron microscopy with negative staining. Cells were lysed enzymatically and treated with lysozyme to remove cell walls, leaving cytoplasmic membranes and flagella intact for imaging. The basal organelles consisted of three main components: a hook (76 nm long, 27 nm diameter) with circular subunit structure, a rod (12 nm long, 11 nm diameter), and a pair of discs. One disc (22 nm diameter) lay immediately outside the cytoplasmic membrane, while the second disc appeared incorporated into or immediately inside the membrane. Hook morphology varied, appearing straight or bent at various angles depending on specimen orientation. The observed ultrastructure matched the De Pamphilis and Adler model proposed for Gram-positive bacterial flagellar basal organelles, with the rod corresponding to the portion passing through the cell wall. The findings resembled those previously reported for Clostridium sporogenes but provided clearer resolution of the first flagellar disc and confirmed the presence of a second disc.

Key findings

• C. chauvoei flagellar basal organelles consist of a hook, rod, and pair of discs arranged in a structure matching the established model for Gram-positive bacteria
• The outer disc measured 22 nm in diameter and lay outside the cytoplasmic membrane, while a second disc was incorporated into or inside the membrane
• The hook structure displayed circular subunits and measured 76 nm long and 27 nm in diameter, with variable morphology from straight to nearly 90-degree bent configurations
• Negative staining with different stains revealed varying structural details, with uranyl formate best resolving the hook's subunit composition