Lecture 6. Bacterial Motility, Introduction To Pili/Fimbriae Flashcards
What does monotriochous mean?
One flagellum
What is an example of a monotriochous bacteria?
Vibrio cholerae
What does amphitrichous mean?
One flagellum at both ends
What is an example of an amphitrichous bacteria?
Campylobacter jejuni
What does lophotrichous mean?
Multiple flagella at both ends
What is an example of a lophotrichous bacteria?
Helicobacter pylori
What does petrichous mean?
Multiple flagella all around bacteria
What is an example of a petrichous bacteria?
E. coli
What is the motility pattern in bacteria?
Alternating between “run” and “tumble”
In terms of bacteria motility, what does “run” mean?
Motor rotates anti-clockwise, flagellar filaments (with left-handed helices) form bundle and propel cell
In terms of bacteria motility, what does “tumble” mean?
Quick reversal of motor to clockwise rotation, produces
twisting force that transforms flagella into a right-handed helix
What does aerotaxis mean?
Movement usually towards oxygen
What does chemotaxis mean?
Movement usually towards nutrients but also away from toxins
What does magnetotaxis mean?
Movement along lines of magnetism
What does phototaxis mean?
Movement towards light
What occurs in chemotaxis?
Bacteria sense changes in nutrient concentration in environment through a set of transmembrane proteins known as methyl-accepting chemotaxis proteins (MCP)
These proteins interact with cytoplasmic proteins which dictates run or tumble
What does MCP interact with?
Sensor kinase CheA, which can autophosphorylate
Attractant: decrease in CheA-℗
Repellent: increase in CheA-℗
How does the motor switch in the flagellum?
CheA-℗ phosphorylates CheY
Only CheY–℗, not CheY, can bind to flagellar motor
CheY-℗ binding effects change from CCW to CW rotation – bacterium tumbles
What dephosphorylates CheY–℗, allowing the CCW motion to resume?
CheZ
How does a bacteria adapt to attractant?
Over time cell integrates attractants/repellants signal via
methylation of MCP
CheR constantly methylates MCP
Fully methylated MCP is insensitive to attractant
What occurs in low attractant concentrations? (high CheA-℗, high CheB-℗)
Demethylation of MCP, increasing sensitivity to attractant (longer runs)
What occurs in high attractant concentrations? (low CheA-℗, low CheB-℗)
High methylation level of MCP, decreasing sensitivity to attractant, increasing autophosphorylation of CheA (more likely to tumble)
Used to stay in a “good” environment
What is CheB?
A methylesterase, is phosphorylated by CheA–℗
Increases methylesterase activity and demethylation of MCP
How does F. johnsoniae glide?
Latex spheres added to F. johnsoniae bind to and are rapidly propelled along cells
Suggests that adhesive molecules move laterally along the cell surface during gliding
What is required for gliding?
Gld genes
3 Gld proteins are components of an ATP-binding-cassette (ABC) transporter
5 Gld proteins are lipoproteins in the cytoplasmic membrane or outer membrane
Disruption of gld genes results in loss of motility
How does twitching motility occur?
Based on type IV pili first extending from cell surface then being retracted, dragging cell along surface
Powered by ATP hydrolysis and retraction proteins control direction of movement
What are gas vesicles?
Protein vesicles that contain gas, which confers buoyancy to the cell
Allow cells to float up to oxygenated water or towards the light
Can be involved in vertical migration in aquatic systems such as lakes
Found in planktonic bacteria (e.g cyanobacteria) and some archaea
What are fimbriae/pili?
Surface appendages, multi-subunit proteins that are not flagella
Implicated in host–pathogen interactions, colonisation, host and tissue specificity (tropism), biofilm formation
Specialised pili involved in genetic exchange between bacteria
How many groups of pili are there?
7
What are the most important pili types?
Type I and type IV
What are fimbriae involved in?
Bacterial adhesion to surfaces in nature
Major determinants of bacterial virulence
Sometimes aid resistance to immune cell phagocytosis
