MBIO 1010 Lecture 11

• Flagellar movement

  energy to turn the flagella comes from the proton motive force

  • gradient of proton (H+) across the cytoplasmic membrane
  • High [H+] outside
  • Low [H+] inside
  • most proteins form a channel that allows H+ to move into the cytoplasm
  • provides the energy to turn the flagellum
• Flagellum turns like a propeller to drive the cell forward
• Flagellar synthesis

  • several genes are required for flagellar synthesis and motility
  • MS ring is made first
  • other proteins and hook are made next
  • filament grows from tip

  must have all the genes
• Twitching and gliding motility do not occur in flagella
• differences in swimming motions

  • peritrichously flagellated cells move slowly in a straight line
  • CCW = counter clock wise
  • in a straight line each time not an overall straight line
  • when all flagella in ccw then will bundle and run
  • when all sprayed out they are cw and tumble
  • polarly flagellated cells move more rapidly and typically spin around
  • reversible flagella
  • at the pole
  • move more rapidly and spin
  • 2 step forward one step back
  • unidirectional
  • only cw
• Gliding and twitching motility

  • Flagella independent motility
  • Slower and smoother than swimming
  • Requires surface contact
  • Mechanisms
  • Gliding-specific proteins for gliding
  • Type IV pili for twitching
•  

  • Twitching motility employs type IV pili
• Gliding and twitching motility

  • These structures require ATP hydrolysis to extend (up to several micrometers) and then retract, causing the cell to move forward; movement occurs in discrete increments.
• • Gliding motility requires a helical intracellular protein track that interacts with gliding motors and extracellular adhesion proteins. The proton motive force drives rotation of gliding motors that translate this force to the helical track, causing adhesion proteins to move in a helical pattern; this results in continuous forward motion and clockwise rotation of the cell
• Taxis: directed movement in response to chemical or physicalgradients• Chemotaxis: response to chemicals• Phototaxis: response to light• Aerotaxis: response to oxygen• Osmotaxis: response to ionic strength• Hydrotaxis: response to water
• Chemotaxis

  • best studied in E. coli (for peritrichous flagella)
  • bacteria respond to temporal (time), not spatial, difference in chemical concentration
  • to a moment in time where there is more
  • run and tumble behaviour
  • attractants and repellants sensed by chemoreceptors
• chemotaxis

  • if no attractant present: random movement
  • attractant present: directed movement
• Chemotaxis

  • directed movement toward an attractant or away from a repellent
  • biased random walk
  • E.coli shows biased random walk toward glucose when there is a concentration gradient
  • the cell still exhibits a series of runs and tumbles
  • if t senses that the [glucose] is increasing:
  • The tumble is delayed = shortened
  • the run lasts longer
  • so they are running more than tumbling
• Measuring chemotaxis

  • measured by inserting a capillary tube containing and attractant or a repellent in a medium of motile bacteria
  • can also be seen under a microscope