2-6 - Movement of bacterial cells.pdf

2-6: Movement of Bacterial Cells Lecture Overview: • The movement of bacterial cells. The structure and function of flagella, the different types of flagellar arrangements and movement, non-flagellar movement, chemotaxis (and other taxis) • Textbook: Chapter 2.9-2.11 Motility in bacteria o Motilit...

2-6: Movement of Bacterial Cells Lecture Overview: • The movement of bacterial cells. The structure and function of flagella, the different types of flagellar arrangements and movement, non-flagellar movement, chemotaxis (and other taxis) • Textbook: Chapter 2.9-2.11 Motility in bacteria o Motility: The ability to propel your own movement Pawlowski et al., PLOS ONE, 2011 o Many bacteria are motile – different movement strategies/mechanisms have evolved o Not all bacteria are motile. E.g. – Yersinia pestis. Other Yersinia are motile – loss of motility of contributes to Y. pestis virulence? Bacterial pathogen Yersinia pestis is nonmotile Movement using flagella o The Flagellum is a large, complex, multi-protein machine that powers bacterial movement. o ~50 different proteins involved in structure/function of a flagellum o Flagellum includes a long, thin filament that acts like a propeller. It is rotated using a motor that is anchored in the cell envelope. o Rotation of flagellum propels the cell through fluids, enabling the bacterium to “swim” through fluids. o Can also be used for “swarming” – coordinated multicellular movement across a solid surface (not discussed in detail here) Different arrangements of flagella Flagella can be built at different positions along the cell – different bacteria have different numbers/arrangements Some bacteria only produce flagella at cell pole. Either single or multiple – generally at one pole, but some have them at both Other bacteria have multiple flagella scattered around cell poles & body A) Peritrichous (many across pole/body) B) Monotrichous or Polar (single – at pole) C) Lophotrichous (many, all at one pole) Not shown – amphitrichous – (both poles) Not shown – atrichous (no flagella at all) textbook fig 2.30 Flagellar movement: peritrichous (E. coli, S. enterica – model systems for motility) Flagella rotate in both directions Longer “runs” – Counterclockwise rotation, helical bundle formed at tail of cell - cell moves forward Short “tumbles” – one or more flagella rotate clockwise – bundle falls apart – bacteria tumbles, assumes new, random orientation Textbook fig 2.33 Motor switching from CCW to CW dictates direction of movement Flagellar movement monotrichous Bacteria with a reversible flagellum: rotation in opposite direction reverses direction of movement Other bacteria have unidirectional flagella. Here, rotation stops/starts. Random movement during “stops” changes direction of bacterium Textbook fig 2.33 Flagella structure - overview ~50 different proteins are involved in the structure/function of the flagellum 3 segments of the flagellum: 1) Filament. Long, thin propeller – drives movement 2) Hook. Adaptor that connects filament to the basal body 3) Basal body. Core of the structure. Powers rotation of filaments Textbook, Fig. 2.34 The flagellar motor o > 20 proteins anchored in cytoplasmic membrane and cell wall o Harnesses proton motive force to drive rotation o Central rod passes through a series of rings: MS ring (cytoplasmic membrane), C ring (cytoplasm) P ring (peptidoglycan) and L ring (outer membrane) o Stator couples flow of protons to rotation of the MS ring – behaves like a “proton turbine” o MS ring rotates rod…and ultimately hook and filament. o L/P rings act like bearings (or bushings) to help rotation o C ring important for: generating torque, switching motor direction, flagellin secretion (see coming slides) Textbook, Fig. 2.34 Gram positive bacteria Gram Positive Flagellum lacks P/L rings – only C/MS rings Flagellar filament - Flagellin o The long filament that drives movement is made of thousands of copies of a single protein called flagellin o Filament is ~5-10 μM long, ~20 nm wide o Filament is rigid, helical and hollow o Free at one end (out in environment) – connected to motor (via rod, hook) at other end o Using flagellin as the filament is conserved in bacterial flagella…but its sequence varies o Detected by our immune systems – important antigen. o Often used in serotyping (H antigen) Textbook, Fig. 2.34 Synthesis of the flagellum o The overall flagellar structure built from inside out – innermost stuff assembles first. o Flagellin (filament) grows from outside. Is produced in cytoplasm & secreted through flagellum via the hollow filament. New subunit assembles at end (outside cell) with help of cap proteins. o “Type III secretion system” used to export flagellin: a related system is used as a protein toxin injection system by certain pathogens Textbook Fig. 2.35 Variations of flagellar motility A lot of different tweaks/mechanisms have been identified for flagellar motility. Some examples: o See previous descriptions (Gram positive rings, different flagella numbers/locations, unidirectional motor rotation) o Some bacteria have motors that use Na+ gradient instead of proton motive force to drive rotation o Spirochetes have a flagellum (“axial filament”) that resides in periplasm – rotation results in corkscrew motion of entire bacterium (useful in viscous liquids) o Flagellar motility if often highly regulated – even motile bacteria can adopt atrichous/non-motile state Taxis Taxis is the directed movement of bacteria. Accomplished using a “bias random walk” Textbook Fig. 2.39 Chemotaxis in E. coli Chemotaxis: Movement in the direction of gradients of increasing or decreasing concentration to particular chemical(s) Chemoreceptors detect specific chemicals (e.g. nutrients such as amino acids) Pass this information on to proteins that control direction of the motor If bacterium moving toward desirable nutrient, tumbles inhibited – longer runs, less frequent tumbles. If moving away – shorter runs, more frequent tumbles. Some other types of taxis Phototaxis: Movement toward/away from light Aerotaxis: Directed motility in response to O2 Generally these operate in a similar fashion to chemotaxis, but receptors detect different kinds of signals Phototropic bacterium Rhodocista centenaria migrating toward light via phototaxis Textbook Fig. 2.41 Other types of motility: twitching motility Some bacteria can move using other types of motility (non-flagellar) This includes twitching motility, in which a Type IV pilus attaches to a surface and then retracts Sort of like a grappling hook Textbook Fig. 2.38 youtube videos to help demonstrate flagella, motility, chemotaxis: Flagella: https://www.youtube.com/watch?v=B7PMf7bBczQ (more detailed info in this than you need to know for this class) Swimming – chemotaxis: https://www.youtube.com/watch?v=-GD0kXgYv2A