L3 - Bacterial function - communicating with the chemical world Flashcards
Why do bacteria compete for occupancy on surfaces like leaves or soil?
Bacteria compete for space to establish themselves in a niche, securing access to nutrients and preventing colonization by other microbes.
How do bacteria fight starvation or nutrient depletion in their environment?
Bacteria constantly metabolize available nutrients and must secure additional resources to survive, leading to continuous competition for nutrients.
Why are bacteria exposed to noxious chemicals?
Bacteria produce harmful chemicals as defense mechanisms, and they are also exposed to toxic compounds produced by competing species.
why is taxis needed for:
1. fighting starvation or nutrient depletion
2. exposure to noxious chemicals
- move to search for nutrients
- move away from toxic environments
what is taxis?
movement towards or away from a stimulus
what are the 4 types of taxis
chemotaxis, aerotaxis, phototaxis, magnetotaxis
What is chemoreppellent and chemoattractant
moves away (chemoreppellent), moves towards (chemoattractant)
what type of experiment can be used to identify chemotactic cells, explain it in detail
capillary tube assay:
- we have a suspension of cells and we are going to plunge a capillary of what we are testing, see how many bacteria is going to enter
- control = filled with same medium the cells are suspended in
- count how many cells are in capillary, after counting the cells:
- less than control = repellent
- more than control = attractant
what are the 3 diff motility modes
flagellar locomotion, axial filament, gliding motility
What structure enables bacteria to move using a twisting motion around the cell?
A long flagellum allows bacteria to move by rotating and propelling the cell forward.
How do bacteria glide using fimbriae?
Bacteria use fimbriae (small pili) as “feet” to attach to surfaces and pull themselves forward, enabling gliding movement.
How does slime or polysaccharide secretion aid bacterial gliding?
Bacteria secrete slime or polysaccharides to reduce surface friction, making it easier for them to glide.
Describe the flagellar locomotion: why can’t it sense conc and what other mechanism does it use
cell length too small to sense gradients so they use biased random walk to sense if its going up or down gradient
describe what the random walk is
- default movement in a liquid
- homogenous/no gradient
- its an endless zigzag path (not completely out of structure)
- at the end of each run, it tumbles in an orientation and it resumes a straight run (straight run + tumble + repeat)
- only achieves by petritrichous bacteria
How is the random walk achieved in peritrichous bacteria
- all the flagella are simultaneosuly rotation anticlockwise, forms a big bundle that propells the cell
- there will be a switch (anticlockwise → clockwise)
- opens flagella (sends cell in uncontrolled spin)
- resumes un as flagella bundles together
What is the distance of the run dependent on
frequency of tumbles. the higher the frequency of tumbles the shorter the run distances
What happens to random walk when an attractant is present?
turns into biased random walk:
- if its moving up-gradient = frequency of tumbles decreases → longer runs
- down-gradient = increase frequency of tumbles = shorter runs
how does the chemosensory signal transduction lead it to go CCW + CW + CCW
normal run:
- motor is counter-clockwise
- cascade of signal from proteins
- last protein = CheY, unphosphorylated in default so it doesnt interact with motor
- CHeA autophosphorylates itself and passes to CheY
- CheY is phosphorylated so motor is clockwise
- only quick because another protein dephosphorylated CheY so it becomes counter clockwise again
How does low conc gradient lead to shorter run?
lower conc = more dephosphorylation = more counter clockwise = shorter run
How does flagellum locomotion work in monotrichous flagellum
- cell simply changes direction
- slight kink at base of the flagella
- cell flicks slightly
What is magnetotaxis
- cells react to magnetic field
- motile and gram negative
What is the magnetosome?
group of metals that are encased in vacuole within cell cytoplasm, those metals align to field creating dipole. uses this as a bio compass
why do bacterial cells like cooperation?
- another strategy cells have is to engage on cooperative behabiour
- more efficent if performed together in concert
How is quorum sensing discovered through vibrio Fischer
- shining takes a lot of energy so its a waste of resource to switch on this gene unless theres sufficient bacteria to make it worthwile
- mantle → has the vibrio fischeri, squid uses its shine to mimic moonlight. adjusts the intensity of the torch tto match the moonlight to deter predator
- bacteria always shines when there is sufficient density
- squid has 2 pouches, one for bacteria one for ink sack
- ink sack modulates the brightness
How does autoinducer work in quorum sensing?
- bacteria capable of quorum sensing produces autoinducer
- can diffuse in and out of the cell
- at low density, less autoinducer
- at high density, more autoinducer
- within tight volume there is high density of autoinducer which switches on
What is quorum quenching?
produces smt that is disrupting another species systems so that species cant quorum sense
A virulence factor of some bacteria includes hijacking of quorum sensing. how is this produced?
- whilst waiting until specific conc?
- switches on virulence at lower density
- engineers commensal bacteria (probiotic) producing autoinducer
- makes them think they have too high density so they never reach quorum sensing
