Bacterial Competition Flashcards
1
Q
Contact independent bacterial interaction
A
- contact-independent
- Diffusible factors
- antibiotics
- bacteriocins
2
Q
Contact dependent bacterial interaction
A
contact dependent
- Direct cell-cell contact:
- Type 5 secretion system
- Type 6 secretion system
3
Q
Protein secretion in bacteria
A
Check notes for diagram
4
Q
Sec secretion
A
- present in both gram positive and gram negative bacteria
- signal peptide (SP) at the N-term of protein marks substrates fro secretion
- SP cleaves off once the protein reaches the periplasm
- there are two variants
- post translational
- co-translational - proteins are secreted in an unfolded state
5
Q
Tat secretion (Twin Arginine Translocation)
A
- Substrate have N-terminal leader sequence with a twin-arginine (“RR”) motif
- secreted proteins are mostly if not fully folded
- suggested to be able to export protein complexes (i.e. Proteins lacking secretion signal can also be exported)
6
Q
Type 1 secretion system (T1SS)
A
- 3 components
1. Inner membrane ABC transporter
2. Periplasmic connector membrane protein
3. outer membrane pore
Large proteins (toxins)
- MARTX toxins from V.cholerae
- alpha -haemolysin from E.coli
Small molecules/heavy metals:
- Multidrug efflux pumps
7
Q
Types 2 Secretion system (T2SS)
A
- homologous to “type IV pili” (the extendable and retractable pili)
- Periplasmic substrates use a pilus to be pushed out of cells - example substrates
- Vibrio cholerae
- Cholera toxin
- proteases
- chitinase - Pseudomonas aeruginosa
- Exotoxin A
8
Q
Type 3 Secretion system (T3SS)
A
- Closely related to flagellum
- directly “injects” effectors into host cells
- responsible for delivery of a wide range of effector proteins
- important for bacteria virulence in many bacterial pathogen : Salmonella, shigella, `yersinia, E.coli (EPEC,EHEC) and others
9
Q
Type 4 Secretion system (T4SS)
A
Check slides, notes and textbooks
10
Q
Type 5 secretion system (T5SS)
A
- autotrabsporter delivered to periplasm by sec
- c-term domain inserts into the outer membrane and acts as a channel for the rest of the protein
- Example substrates:
- Adhesins
- proteases
- contact dependent inhibition
11
Q
Bacteriocins
A
- bacteriocins are toxic proteins or protein complexes synthesised by bacteria to kill competing bacteria
- bacteriocins are typically not toxic to the strains that produce them
- species- specific and sometimes strain specific
- Typically require a specific receptor in order to intoxicate a cell
- frequently are specific for the species that produce them
12
Q
Bacteria in structure
A
Check notes for diagram
- Receptor domain allows the colin to bind to the target cell
- Translocation domain facilitates entry of the Activity domain into the target cell
- bacteriocins that are found in E.coli and called colicins
13
Q
Bacteriophages
A
- bacterial viruses
- particles comprised of protein and nucleic acid
- Basic lifecycle:
1. Attach to the surface of specific bacteria
2. inject their genetic material
3. hijack host replication and translation machinery of host cell
4.Produce more phage particles
5. lyse the host cell to release the newly made phage
6. newly released phages can infect new cells
14
Q
Lysis and plaque formation
A
- Initial infection
- Lysis of infected cell, secondary infection of neighbouring cells
- Clearance of bacteria results in a clear “hole”
15
Q
Contractile tailed phage
A
- Phage need a “receptor”
- no attachment = no infection
16
Q
Lysogenic vs lytic life cycles
A
- “Virulent” phages are lytic only
- temperate phages are both lytic and lysogenic
- lysis is achieved through endolytic enzymes
17
Q
Phage aren’t the only things that “infect bacteria
A
Bdellovibrio are motile Gram bacteria that invade and grow within other bacteria (bacterial parasites of other bacteria)
18
Q
Pyocins
A
- pyocins are bacteriocins produced by Pseudomonas aeruginosa
- There are multiple types of pyocins
19
Q
S-pyocins
A
S-pyocins are like the colicins that we talked about earlier (check notes)
20
Q
R-type pyocins
A
- R-Type pyocins resemple contractile tailed phages that lack the phage head
- attach to the outside of target cells, insert into the membrane and create a channel for cellular contents to flow out
21
Q
A
22
Q
TS66
A
- related to contractile phage
23
Q
T6SS sheath assembly in Vibrio cholerae
A
- Polymerizes from the membrane out in ~30s
- contracts to ~50% in less that 5ms
- Disassembles in ~30s
- Whole cycle restarts at apparently random location
24
Q
Measuring T6SS cell killing
A
Killing is contact dependent
Check notes and textbook
25
T6SS delivers multiple ‘loaded’ toxins with each secretion event
Check notes and textbooks
26
T6SS range of attack
- can reach ~½ of a cell width around it
- does not require a receptor (any cell can be hit… even eukaryotic cells)
- Requires target to be adjacent and stably associated (bacteria can’t just be floating in solution)
27
Contact dependent inhibition (CDI)
Check notes
28
Toxic activities of bacteriocins, CDI and T6SS
- tRNase (bacteriocins, T6SS, CDI)
- pore-formation
- DNase
- rRNase
- Peptidoglycan hydrolase
- Lipases
- other activities, peptidase, deaminase, ADP-ribosyltransferase, etc. (Identified in genomes for T6SS)
29
Anatomy of a bacterial cell and bacterial cell wall
Check notes
30
Bacterial cell wall - gram positive
Single membrane
Thick peptidoglycan
31
Bacterial cell wall - Gram positive
Single membrane
Thick peptidoglycan
32
Bacterial cell wall - gram negative
Double membrane
Thin peptidoglycan
33
Bacterial cell wall - Mycobacteria
Single membrane
Thin peptidoglycan
Thick mycolic acid layer
34
Targeting the cell wall
- many bacteria with a T6SS delier peptidoglycan hydrolases that degrade cell wall. Some cleave the peptide linker while others cut the glycan chains
- Antibiotics can produce a similar cell rounding effect by disrupting cell wall biosynthesis (blocks the formation of the peptide linkage)
35
Cell wall protects against osmotic stress
Check notes
36
Beta -lactam antibiotics
In 1929, Sir Alexander Fleming observed that the fungus penicillium natatum produced a compound that inhibited growth of staph
37
Bacteriostatic or bacteriocidal
Check notes
Bactericidal - kill all of them
Bacteriostatic
38
Are beta lactams bacteriostatic or bactericidal?
Bactericidal mostly
- if a cell is growing the antibiotic beta lactams are bactericidal. The faster it is growing the more bactericidal they become
- but in a population of bacteria, not ALL bacteria will be actively growing
- Some will naturally end up growing slower because of nutrient deprivation, stochastic mutations, variation in gene regulation etc.
- these bacteria are called persister cells or just persisters
39
Targeting the call membrane
- some bacteria with a T6SS deliver lipases that degrade membranes
- this causes cell membranes to shrink until osmotic pressure rupturs them
- Triclosan inhibits fatty acid biosynthesis necessary for building/repairing cell membranes
- Was frequently used in soaps, toothpaste, surgical cleaning
- not so common anymore as concerns abouth secondary effects on people have been raised
40
Are membrane disrupting toxins and antibiotics bacteriostatic or bactericidal
bactericidal at high enough concentrations
41
Targeting translation
- tRNase; rRNases - many bacteriocins/T6SS
- several different families of antibiotics block protein synthesis by binding to and inhibiting different ribosomal subunits
- bacteriostatic vc bacteriocidal? Depends on the antibiotic and depends on the concentration
- Bacteriostatic:chloramphenicol, macrolides (e.g. Erythromycin), tetracycline
- bactericidal: aminoglycosides (e.g. Gentamicin)
42
Targeting DNA
- some T6SS toxins can degrade DNA
- Quinolone s(e.g. Ciprofloxacin)target DNA winding/unwinding enzymes (DNA gyrase, topoisomerase)
- these enzymes act by cutting and then re-ligate DNA to introduce or relieve supercoiling
- quinolones (bactericidal for growing cells) inhibit just the ligase activity
- as a result single and double strand breaks are introduced into the chromosome
43
Measuring antibiotic resistance
- Disc diffusion assay
- coat an agar plate with bacteria
- embed antibiotics in a paper disc
- antibiotics will diffuse out of the disc and prevent growth in an area
- bigger radius = lower more potent killing (less resistance)
44
Measuring antibiotic resistance
Minimum Inhibitory concentration (MIC) assay
- serially dilute the antibiotic
- inoculate each dilution with a standard amount of bacteria
- identify the antibiotic concentration at which most bacteria do not grow (usually measured by culture turbidity)
45
Tolerance vs resistance vs persistence
Rewatch lecture
