Lecture 5: Motility and chemotaxis in Bacteria

bacteria can respond to their environment by sensing what? (5)

Physical signals (temperature, pH, osmolarity, etc)

Chemical signals (nutrients, toxins, signalling molecules etc)

Responses at the level of gene expression

Responses at the level of cellular structures

Implies the existence of a sensing system

what is the definition of motility?

ability to move independently using metabolic energy

what are the 3 different types of motility?

Flagellar motility

Gliding motility

Twitching motility

what is flagellar motility?

powered by the movement of flagella

what is gliding motility?

sliding or gliding movement on surfaces using slime. Flagella independent.

what is twitching motility?

propelled by the extension, tethering and retraction of type IV pili (like a fishing rod). Flagella independent.

Motility is important because? (5)

allows movement to favourable environments like host cells

adherence and colonisation → flagella allows bacteria to move towards host surfaces and then adhere to them

nutrient acquisition

evading harmful substance

evading predators or parasites but some bacteriophages have evolved to attack bacteria by flagella, so double edged sword

what are the 4 ways in which flagella can be displayed on bacteria? Give an example of bacteria for each

Monotrichous (polar) → Vibrio cholerae

Lophotrichous → Pseudomonas fluorescens

Amphitrichous (bipolar) → Campylobacter jejuni

Peritrichous → Escherichia coli

does the arragement of flagella on bacteria change between species?

yes it is species specific

is it costly to move flagella?

very energetically expensive to move flagella, so about 2% of energy made goes towards flagella movement

what energy is used to move flagella?

proton motor force

what are the 3 different parts of the motor of flagella? and where are they each located?

the filament → exposed in extracellular medium

the hook→ protrudes out of cell envelope

the basal body → embedded in the cell envelope

what is the structure and composition of the filament? what is a special thing about the protein which makes the filament?

rigid structure with constant width

made of flagellin protein arranged in helical hollow structure

filament diameter and helical curvature can change between species

During synthesis, flagellin proteins move through the hollow core to the growing filament tip

what is the structure, characteristics and composition of the hook?

its is a joint that joins basal body to filament

Flexible

Slightly wider than filament

Connects filament and the basal body

Composed of FlgE protein subunits

what does the basal body cosist of? what is the difference in gram negative and gram positive bacteria?

Consists of a central rod and system of rings
20 proteins
Gram-negative: 2 pairs of rings
Gram-positive: 1 pair of rings

using e.coli explain the structure of the basal body, what are the three parts and their main characteristics?

Bushings= L+P ring

Rotor (rotates)

Stator (static)

describe the bushings and the different strcuture in is as well as what they are made of and where they are found. In which type of bacteria are these rings found?

L ring is made of FlgH and is found in the outer membrane

P ring is made of FlgI and is found in the peptidoglycan layer

Absent in Gram + bacteria because they have no outer membrane

describe the structures in the rotor, as well as what they are made of and where they are found.

MS-ring made of FliF and is found - Inner cytoplasmic membrane

C-ring made of FliG, FliM and FliN. It is found in the cytoplasm → it controls the direction of rotation

describe the structures in the stator as well as where it can be found.

Proton-powered stator units (MotA-MotB) which powers the rotor.

Attached to peptidoglycan layer

describe how the flagella use the motor to move.

protons move through stator (MotA and MotB) by proton motive force

Protons bind to conserved aspartic acid in MotB protein

This binding causes a conformational change in MotA that moves the rotor

what are phase variations?

bacteria can alter expression of their gene

give an example of where a bacteria uses phase variation to evade host defenses.

ex: salmonella typhi:
Flagellin protein (FliC) is an antigen, recognised by Toll-like receptor 5 (TLR5)
Salmonella typhi can replace FliC with an alternative, antigenically-distinct subunit protein, FljB →The random switching between FliC and FljB may help Salmonella to evade host defences and is called 'Phase Variation

what is chemotaxis?

the movement of microorganisms, particularly bacteria, toward favorable chemical environments while avoiding harmful substances

describe the experimental evidence of chemotaxis.

beaker with bacteria and capillary tube with control, then another beaker with a capillary tube with attractant and then another with a repellant

it can be seen that bacteria in control are evenly spaced, in the attractant bacteria go to the tube and the repellant the bacteria move faraway from tube

explain/describe peritrichous flagella movement.

Flagella move counterclockwise, forming a single bundle that propels cell in long straight runs
Movement stops when some flagella rotate clockwise, disengage from the bundle, and trigger a tumbling motion
A tumble only lasts about one-tenth of a second and no real forward progress is made.
After a tumble, the direction of the next bacterial run is random
bacterial will sense movement in a favourable direction and tumbling will be suppressed while runs last longer
bacteria move in this specific way even though they want to go in a straight line because of brownian motion which explains how small particles will deviate from a straight line

describe the movement of monotruchous/polar flagella

reversible flagella
anticlockwise propels bacteria forward
clockwise propels bacteria backward

irreversible flagella
clockwise propels bacteria forward
for them to change direction they must stop and reorient

so bacteria can move up or donw gradients to get closer and futher away from things, how does the bacteria know where to go towards the substance of away?

The two component signalling system (most common form of signalling pathway in bacteria)

what is the two component signalling system mediated by?

transmembrane receptor and a phosphorelay system

what is the sensor in the two component signalling system?

Membrane bound histidine kinase (e.g. CheA)

what is the response regulator in the two component signalling system?

mediates response via altered expression of genes

in the case that the substance is a repellent, explain how bacteria can alter their movement to move away from substance.

ligand binds and MCP forms a dimer and recruits CheW and CheA

CheA (sensory kinase) autophosphorylates

CheA transfers P to CheY

CheY phosphorylates fliMGN

fliMGN signals to flagella basal body to switch rotation from counter clockwise to clockwise → bacteria gets away from repellent

in the case that the substance is an attractant, explain how bacteria can alter their movement to move towards from substance.

MCP does not form a dimer, and CheA is not autophosphorylated

CheA does not transfer P to CheY so flagella does not change direction

CheZ stimulates the dephosphorylation of CheY so there is less tumbling

do all attractants and repellants have the same signal transduction?

no, specific attractants and repellants have their own signal transduction for example:

aspartate and glutamate go through Tar → Che → Fla

serine, alanine, glycine, aminoisobutyrate Tsr → Che → Fla

galactose and glucose GBP→Trg→Che→Fla
dipeptides DPP->Tap→Che→Fla