Motility Regulation L11 Flashcards
what is bacterial motility
control of gene expression and adaptation to the environment
what must be achieved for flagellum components to be produced in correct order
temporal gene expression
what is the internal structure of flagellum like
genes required for assembly of each part of the flagellum need to be produced in a specific order
what is RNA polymerase holoenzyme like
consists of six protein subunits
Core enzyme (five subunits)
Sigma factor
what does the sigma factor bind to in transcription
-10 and -35 sequences in bacterial promoters and identifies the beginning of a gene
what does sigma 28 control production of
Structural genes for flagellin production
what prevents the structural flagellin genes being expressed
not expressed until basal body is complete
where is sigma 28 in cell
σ 28 is made continuously by the cell but is bound to an ANTI-sigma factor protein (FlgM)
what happens when basal body is complete
FlgM is exported from cell
σ 28 released and induces expression of the structural genes
what causes temporal gene expression
Mechanism ensures that flagellin is made after the basal body is formed
Results in correct temporal gene expression
what are the steps that occur during temporal gene control of flagellum assembly
σ28 and FlgM (anti-sigma factors) made
FlgM stops σ28 binding to promoters = no flagellin synthesis
Basal body is made using σ70 = no flagellin synthesis as inside cell FlgM conc high
FlgM exported through basal body
Flagellin gene induced by free σ28
flagellin exported, flagellum assembled
what is flagellin
surface antigen
H antigen
what is the benefit of variable flagellum
when bacteria encounter host will want to invade immune system
variable flagellum good as if already seen flagellum will destroy but if different will not as not seen before
what os E.coli O:157 H:7
Flagellin is H antigen flagellin variant is 7
O:157 is numbered variant of LPS
what do many pathogens do to prevent detection
many pathogens switch OFF flagellin genes in response to signals that indicate they are inside a host cell
what are the two modes in bacterial swimming
swim forward
tumble
how does a change in mode occur in taxis
altering direction of rotation of flagellum
what does anticlockwise rotation cause
smooth swimming
what does clockwise rotation cause
induces tumbling
what happens when polar flagellum in anticlockwise rotation if change the direction of rotation
cell moves backwards and induces turning cell starts to reorientate
once reorientated will change rotation again and swim in new direction
what happens when peritrichous flagellum in anticlockwise rotation if change the direction of rotation
cell moves backwards
flagella unbundle = unstructured, induces turning change direction, totally random
get reorganised
what happens to the bacteria after tumbling
bacteria randomly re-initiates forward movement
how does taxis allow movement in chosen direction
bacteria capable of swimming towards an attractant or away from a repellent
frequency of running and tumbling is altered by environmental signals
when is straight running favoured
is more of the attractant than previously sensed then the cells is heading in the right direction
when is tumbling favoured
less of the attractant than previously sensed then the cells is heading in the wrong direction
what does gradual drift towards attractant cause
‘biased random walk’
how do bacteria respond to attractant stimuli
head towards
how do bacteria respond to repellent stimuli
head away
how do bacteria respond to neutral stimuli
ignore
how do bacteria respond to chemical stimuli
chemotaxis
how do bacteria respond to light stimuli
phototaxis towards lioght
how do bacteria respond to gas stimuli
oxygen
aerotaxis
how do bacteria respond to magnetic field stimuli
magnetotaxis
what are the two ways to determine is you’re going in right direction when sensing chemicals immediately next to you
Spatial sensing
“Memory” sensing
how do bacteria sense difference in chemical conc along their length
Bacteria are generally ~ 1 µm long
can’t sense chemical concentration differences along their length
must use a “Memory” method
how is taxis controlled - regulation of swimming
using a set of sensory and regulatory proteins
Directly controls motor rather than changing gene expression
what does control of taxis require
two components
A and B
where is A component located
cell surface
where is B component located
in cytoplasm
what is A component
MCP = Methyl-accepting Chemotaxis Protein
sensor protein which responds to stimulus
what is B component
- CheA/CheY = phosphor transfer system in cytoplasm
- CheY = induces switching of motor direction
- CheZ = system reset
what occurs in control of taxis
stimulus outside, detect something like
signal transferred to Che A on inside, becomes phosphorylated
phosphate group transferred to Che Y = Che Y-P
Che Y-P induces a tumble, motor change
Che Z removes Che Y-P to Che Y, lets motor to return to CCW rotation
where is C component
Alsp located in cytoplasm
what occurs in C component
CheR = methylating protein that modifies MCP CheB-P = removes methyl groups
what occurs in control of taxis when interact with attractant
remember have sensed attractant
Che R add methyl groups to MCP inside, get it to give signal to Che A needs more attractant
Methylated – need more molecules to change shape (desensitised)
need to reset system – use Che B
Che A deliver a phosphate to Che B
Che B-P made will start removing methyl groups
what is memory sensing
compare the concentration that there is now with what was sensed previously
what is needed for memory sensing
need chemical gradient along the length of the body
what is spatial sensing
‘head’ end indicates there’s more chemical next to it than next to the ‘tail’ end of the cell
