Facultative structures Flashcards
What structures can bacteria contain for specific metabolic functions?
Carboxysomes - Photosynthesis dark reactions.
Pigments/Chromatophores
What facultative structures are in bacteria for survival/protection/defence?
Polysaccharide capsule
Plasmids
Storage granules
SPORES
What facultative structures of bacteria serve for motility?
Flagella
PILI
Gas vacuoles
What are endospores?
Resistant, tough NON-REPRODUCTIVE structure.
Produced mostly by Gram +ve bacteria.
Structure differentiated from vegetative cells.
Which are resistant to severe conditions and can be identified by their position in the mother cell…
How can endospores be identified?
Do not show in Gram Staining:
Instead, using Witz staining:
Using heat and malachite green, counter stained with Fusein.
What is the general structure of endospores?
A facultative, loose Exosporium surrounds the endospore.
TUNIC = A thick, waterproof, layers of protein.
= RESISTANCE
Cortex - can occupy 50+% of spore volume.
= Contains a peptidoglycan, and surrounds classical structures like PM, ribosomes, nucleoid.
A dehydrated Core = Cytoplasm.
= MORE RESISTANT TO HEAT>
What substances are found in Endospores?
The core = dehydrated cytoplasm
= In order to provide heat resistance and avoid boiling water in cytoplasm.
(only 20% water, vs 80% elsewhere and normally)
Cytoplasm has high Ca2+ conc. which is contained by dipicolinic acid = heat resistance.
Small-Acido soluble proteins (SASPs) protect DNA against heat.
How does the endospore form?
Hostile conditions, promote the start of sporulation cycle
(Forming endospores)…
= Exiting the vegetative cycle.
First, there is chromosomal duplication and assymetric cell division.
= Forming the forespore.
The mother cell engulfs the Forespore - with formation of the different surrounding layers e.g. Tunica, Cortex, Exosporium.
When Endospore has matured, the mother cell will undergo lysis and release the endospore.
After dormancy, favorable conditions will promote germination of spore.
How does the endospore germinate
In favorable conditions, the dormant endospore will start germination.
= To emerge as a vegative cell and recommence vegeative growth.
1
Activation = Tunica of spore lyses by environmental factor like shock, heat, acidity…
- The cortex is removed and the the core is hydrated… IF IN FAVORABLE CONDITIONS… nutrients like AAs, Mg2+, adenosine.
3
Growth - biosynthesis activated.
How can endospore be destroyed?
Tyndallization - process of spore removal.
Discontinous heating at low temp, then short burst of hot for 30 mins every day… Over 3 days.
Encouraging spore germination at lower temp, but vegetative cells die off in heat.
What is difference between chemotactism and motility?
Motility is ability of some bacteria to make own movements.
Chemotaxis - is movement in response to attractants/repulsants.
What are the different forms of motility?
Swimming - requires flagella
Gliding - secrete polysach.
Social gliding - traction by Type 4 pili.
Vertical - Gas vacuoles.
Magnetic - Magnetosomes.
Do archaeea have flagella?
Archeae can have flagella
Thinner than bacterial flagella (10-12nm diameter).
Similar to Type 4 pilus.
A full extracellular organite.
Rotation is not powered by PMF, but ATP hydrolysis.
What are the different secretion systems?
Flagella are modified Type III secretion systems.
T3 secrete adherence proteins.
Salmonella have T3 secretion systems to inject virulence factors into host cells.
Type 4 secretion systems secrete proteins/nucleoprotein complexes.
How do spirochete flagella differ from other bacterial flagella?
Bacterial flagella are anchored to cytoskeleton, so originate from cytoplasm. In Spirochetes, flagella can be periplasmic = enable viscous environment motility.
How do the structures of flagella compare between Gram -ve and Gram +ve?
Gram -ve are more complicated due to outer membrane.
Gram -ve bacteria have 4 rings (L, P, MS and C rings)
But Gram +ve have 2 rings only (C and MS)
With flagellin forming the filament as structural protein.
What is the structure of Gram -ve bacteria?
4 rings in Gram -ve:
L ring in outer membrane
P ring in peptidoglycan
C and MS rings in PM.
(Gram +ve have C and MS ring).
with basal body, hook and filament.
Filament is longer than length of bacterial body itself.
Cap protein.
Filament of Flagellin.
What genes encode for flagellum proteins?
How does Flagella filament form?
FliE is gene encoding for flagellin protein, which comprises the filament.
FliD gene encodes for filament capping protein, which directs assembly of flagellin…
Assembly does not require ATP.
How is bacterial flagella powered?
Whilst flagella assembly does not need ATP, the rotor motion needs ATP to establish PMF.
Protons flow down conc. gradient through Mot protein, which acts as driving force for rotor rotation.
How does CW and CCW rotation affect movement?
CCW rotation = forward propulsion, swimming.
CW rotation = tumbling, random reorientation and turning.
What determines the rate of tumblng and swimming?
When there is no gradient of nutrients, tumbling frequency is greater and bacteria make shorter linear movements.
In a gradient of attractants, positive chemotactistm has longer linear moevements and reduced frequency of tumbling.
What is phototaxis?
Photosynthetic bacteria can respond to different wavelengths of light.
Use light activation as initiator of motility.
What is the process of chemotaxis?
Swimming is default - requires repulsive signalling to trigger tumbling.
Transmembrane chemosensors attach sensor molecule.
Receptor is phosphorylated and kinase is activated.
CheW activates CheA, the sensor kinase.
CheA phosphorylates CheY.
Phosphorylated CheY binds to basal body of flagella, triggering CW rotation and TUMBLING!!!
When chemosensor is no activated, there is no CheY activation.
- NO CW rotation induced, so CCW rotation = Swimming…
How can chemotaxis be modified?
CheB can methylate Chemosensor receptor.
= Reduce sensitivty of receptor.
= More swimming.
CheR can methylate receptor to increase receptor sensitivity.
