Flagellar Arrangements 2 (a): Source: Louisa Howard/Dartmouth Electron Microscope Facility; Flagellar Arrangements 3 (b): Heather Davies/Science Source Flagellar Arrangements 4 (c): From: W.J. Strength and N.R. Krieg”, “Flagellar activity in an aquatic bacterium”, “Can. J. Microbiol. May 1971, 17:1133-1137, Fig. 5. Reproduced by permission of the National Research Council of Canada”; Flagellar Arrangements 5 (d): PTP/Phototake Flagellar Responses 1 Guide bacteria in a direction in response to external stimulus: • Chemical stimuli – chemotaxis; positive and negative • Light stimuli – phototaxis Signal sets flagella into motion clockwise or counterclockwise: • Counterclockwise – results in smooth linear direction – run • Clockwise – tumbles Flagellar Responses 2 Key Flagellar Responses 3 a) No attractant or repellent Flagellar Responses 4 b) Gradient of attractant concentration Periplasmic Flagella 1 Internal flagella, enclosed in the space between the outer sheath and the cell wall peptidoglycan Produce cellular motility by contracting and imparting twisting or flexing motion Periplasmic Flagella 2 (a): Courtesy of Dr. Misha Kudryashev and Dr. Friedrich Frischknecht, Mol Microbiol, 2009 Mar; 71(6):1415-34.