2 - Biomechanical World of Bacteria - Egbert Flashcards
in what aspects of bacteria life (both intracellular and extracelular) does physics play a role? name the active and passive processes
INTRACELLULAR;
- active; chromosome segregation, protein transport
- passive; diffusion, quantum mechanics of biochemical reactions
EXTRACELLULAR;
- active; mechanical forces generated during cell motility eg gliding, pilus retraction, flagella motility
- passive; environmental specific mechanisms eg hydrodynamic forces, adhesive forces
what is Reynold’s number? give examples of 2 organisms, state the Reynolds number @ which they live at
- dimensionless number comparing the magnitudes of inertia and viscous forces in a given flow. therefore allowing us to quanitfy the relative importance of these 2 forces
HIGH REYNOLD’S NUMBER; - whales
- > 10^4
- dominated by inertia. therefore if to stop swimming in water then wouldnt come to a straight stop, would keep floating
LOW REYNOLD’S NUMBER; - bacteria
- < 10^-3
- bacteria will come to a stop instantly if stop moving. dominated by viscosity
what would happen if we were to live at low Reynold’s number?
- would experience Brownian motion as a result of non-uniform collisions with water molecules
- water would have the viscosity of molasses (hence why bacteria stop immediately when stop swimming)
- if we were to stop swimming, come immediately to .a halt
how do bacteria cells swim? in terms of Brownian motion etc
- brownian motion causes the bacteria to rotate
- bacteria propel themselves using flagella
what does a large Reynold’s number mean for the body shape of aquatic animals?
all in a streamlined shape
what does a small Reynold’s number mean for the shape of water-living microorganisms?
can adopt any shape they want because inertia does not play much of a role
not required to be streamlined because not important
different shapes adapt to different conditions
how does a scallop swim?
draw a diagram showing scallop direction at R both below and above 1
- swims in a reciprocal motion
- opens shell then quickly closes it by squirting water out
- 328 - 2 word
what does reciprocal mean in terms of movement?
changing its shape then returning to the original shape by going through the change in reverse
at low Reynold’s number, what type of movement works?
the movement can not be reciprocal
- based on the fact that inertia plays no role in movement
draw 3 hypothetical flagella structures. 2 must not be able to move @ low R and 1 must be able to move
328 . 2 word
give examples of 2 types of prokaryote that follow gliding motility. draw diagrams of each of their motions
eg cyanobacteria and myxobacteria
word
describe 3 hypothetical models of how gliding motility might work
FOCAL ADHESION;
- cells make contact points to the substrate which is anchored to the cytoskeleton proteins
HELICAL ROTOR;
- surface is deformed when the larger complex pushes into it and pushes the cell along
- the smaller complex does not affect the movement because it does not push into the substrate
NOZZLE;
- slime secreted from the back and the extension of the T IV pili and retraction helps to push the cell along
328 - 2
name the 5 physical phenomena that affect single bacteria on surfaces. draw a diagram to summarise these and show which direction the force is going
- adhesion
- shear stress
- rheology
- advection
- diffusion
state the 3 main ways in which single cells can leverage fluid flow and give examples
- surface colonisation eg Caulobacter crescentus
- attachment through catch bonds eg E. coli
- flow-directed movement eg Pseudomonas aeruginosa
how does fluid flow play a role in the attachment of C. crescentus?
the flow forces the cell to the bottom of the mix therefore allowing the holdfast to bind to the surface
draw the stucture of C. crescentus attached to a surface
word
how does E. coli attach to surfaces? draw a diagram
through catch bonds
- FimH extends from FimA (stalk)
- in the low affinity structure, FimH is compressed. when in high affinity state it is in an elongated form
- when we apply force FimH starts to close around the mannose hence why we see that protein attachment is directly proportional to the force applied
328 - 2 word
draw a graph of no. E. coli adhered to a surface against shear stress and explain relevant points of the graph
328 - 2 word
which infections do the development of catch bonds play a role in?
E. coli infecting urogenital tract -> UTI
- even more handy because greater attachment with flow of urine
draw a diagram and explain the movement of P. aeruginosa. DAG of this movement
- T IV pili extend out and make connections with surface
- pili disassemble and reassemble to pull the bacteria along the surface
- this is AGAINST THE FLOW
328 - 2 word
draw a diagram of a bacterial community grouped together on a surface. what is the name given to these?
biofilms
328 - 2 word
what are the 5 physical phenomena affecting cell communities on cell surfaces?
- adhesion
- shear stress/flow
- rheology
- advection
- diffusion
give an example of an organism, that in a biofilm state can form a fluid channel. DAG of this fluid channel formation
B. subtillis
which bacterial species can form streamers? DAG of where these streamers are located within pipes and state what the initial steps are involved in this colonisation
- P. aeruginosa
- settle and form streamers where there is less flow because can attach > easily. then we get replication and colony growth
328 - 2 word
give a species that is involved in produce/cheater interactions and DAG of this interaction and explain it
- Vibrio cholerae
DIFFUSION; - producer cells initially adhere to the surface. release of carbohydrates eg GlcNAc attract other cheaters to the site where it is adhered.
- cheater cells are dominant
ADVECTION AND DIFFUSION; - when flow applied, the GlcNAc is washed away as well as the cheaters because no carbohydrate left
what does M. xanthus form when under conditions of stress/starvation?
fruiting body, masses of cells all contained within one body.
inside, some differentiate into spores however around 80% die to provide nutrients etc for the other cells -> cooperativity
give 2 examples of when the shape of colonies is influenced by the physical forces of flow etc
biofilms eg V. cholerae
and streamers eg P. aeruginosa
