Practice question

Spirochaetes constitute a distinct phylum defined by elongated helically coiled cells possessing unique motility apparatus: periplasmic flagella or axial filaments anchored at cell poles wrapping around protoplasmic cylinder within outer membrane periplasm. Rotation generates corkscrew movement enabling penetration through viscous mucus and connective tissue barriers efficiently. Ultrastructure includes flexible peptidoglycan, outer sheath with less lipopolysaccharide, and cytoskeletal proteins determining helical amplitude and wavelength. Genera include Treponema, Borrelia, Leptospira, and Brachyspira, causing syphilis, Lyme disease, leptospirosis, and intestinal spirochetosis in diverse animal hosts and humans.