Bacterial motility, chemotaxis Lengeler et al. Chapter 20, p Global regulatory networks and signal transduction pathways

Basic mechanisms of motility Flagella, rotation Chemotaxis Flagellar motor

Basic mechanisms of motility Swimming –Liquid environment, low viscosity –External flagella –10 to 20 μm / sec – = 10 to 20 body lengths / sec –bacteria: E. coli S. typhimurium B. subtilis

Turning screw –Viscous environment –Endoflagella in periplasm Anchored in CM Extend “half way” along cell length Twist –1 to 2 μm / sec –Spirochetes: Treponema pallidum

Gliding motility –Liquid / solid interface –No flagella –0.2 μm / sec –myxobacteria, cyanobacteria

Locations of flagella Polar –Caulobacter –Pseudomonas Medial –Rhodobacter Peritrichous –Proteus vulgaris; 100s per cell –E. coli; 6 to 8 per cell

swimming Mechanism –Rotation of flagella –Energy: pmf –H + flux drives rotation of motor –Long filaments

rotation Directions of movement –changes frequently –CW, CCW Expt 1 –Latex bead –Coat with α – flagellin antibodies –Bead binds to flagella –Spinning of bead  rotation of flagella

Expt 2 –Glass slide –Coat with α – flagellin antibodies –Cells tethered by layer of ab’s –Cells rotate: 100 Hz = 100 cps –Spinning of cells  rotation of flagella

CCW  CW  CCW 1 to 2 sec 0.1 sec 1 to 2 sec CCW rotation of flagella –Smooth swimming CW rotation of flagella –Somersault = tumble

Random walk –Homogeneous environment; unbiased CCW = smooth –filaments intertwine –Bundles –Propeller CW = tumble –Each flag. pushes in different direction –No bundles

gradients Chemical stimulus –Attractants Nutrients: aa’s, sugars –Repellents Phenol, organic acids, Ni ++, Co ++, some aa’s Response = biased random walk Chemotaxis = directed movement –Towards an attractant, away from repellent

Expt 3 –Fill capillary tube with maltose –Insert capillary in drop of E. coli –Gradient of maltose: Diffuses [high] …….[low] –Cells swim into capillary –Longer runs in “right” direction –Shorter runs in “wrong” direction

Chemotaxis system ~ 10 different proteins Detect and respond to [changes] Different attractants, repellents Send signals to flagellar motor Controls motility system

Motility system Structural components –Basal organelle 4 rings + central rod Embedded in cell envelope Rotor –12 flg genes –4 flh genes –18 fli genes

Energy transducing components –H + to drive flagellar rotation –stator –MotA Proton pore Spans CM –MotB Anchor for MotA Switch components –Determines direction of rotation –FliG, FliM, FliN

Assembly_basal organelle M ring  CM S ring (superficial) inserted Central rod added, capped P ring (peptidoglycan) L ring (LPS) Hook linked to central rod Flagellar filament assembled Mot proteins