Bacterial communication - Lecture 4 Flashcards
Cooperative interactions
allows bacteria to coordinate group activities
Antagonistic interactions
Interactions which exclude species that are detrimental to the community
Types of microbial communities
Polymicrobial communities: variety of species contribute mutually beneficial traits
Single-communities: self-sufficient communities that use kin-recognition, (e.g., Myxococcus Xanthus)
What is quorum sensing
The signalling pathway that orchestrates gene expression for collective behaviours among bacteria
Quorum sensing model for gram-negative bacteria
use of byproducts of metabolism, signal synthase releases signals and signal receptor binds signals that enter the cell
A Signal receptor is a transcription factor, that binds to activate expression of quorum- induced genes
Quorum sensing model for gram-positive bacteria
Transporters release precursor peptides since signals are not permeable through PG. Precursor peptides are transcribed by autoinducer peptide genes
Peptides bind signal sensor (receptor) leading to phosphorelay, phosphorylation of the response regulator and activation of target genes.
Acyl hormoserine lactone
Autoinducer-1 produced by Gram-negative bacteria.
How is AHL produced and how does this lead to production of Luciferase?
LuxL (cytoplasmic enzyme) forms AHL by combining fatty acyl chains and homoserine, constitutively expressed at basal levels
AHL builds up on the medium as more bacteria accumulate
AL diffuses into medium, once threshold is reached (quorum), AL binds to activator LuxR
Leads to increased transcription of Lux operon genes
LuxAB: luciferase
LuxG: Flavin reductase
LucCDE: fatty acid reductase complex
How does Luciferase produce light and how are intermediated recycled
LuxAB oxidized fatty aldehydes to produce fatty acids, light and water while oxidizing flavin
LuxCDE: recycled fatty acid chains produced into fatty aldehydes for subsequent oxidation
LuxG: Reduces flavin from oxidized from for recycling
Applications of Acyl homoserine lactone
Found in A. Fischeri, colonizes light organ of Hawaiian Bobtail squid. Squid is nocturnal and hunts at night
Moonlight shadows of squid alerts prey to its presence and makes it vulnerable to predators
Counterluminescence of the squid uses luminescence of light production to hide its own shadows
What quorum sensing system does Pseudomonas aeruginosa use for virulence?
The Las and RhI system
Las and Rho are integrated and hierarchal quorum sensing systems. Las must be active for RhL quorum sensing and expression of the RhL operon
How does the Las regulon turn on the expression of the RhL operon?
LasI gene is transcribed into the signal synthase (lasL). LasL diffuses into the cell and binds to LasR (TF)
When a quorum is reached LasR binds to and initiates the transcription of RhIR and RhII
RhII (signal synthase) synthase signals are released them from cells, signals diffuse back into the cell and bind to the TF: RhiR which binds to and activates expression of the RhI operon
Expression of the RhL and Las operon leads to induction of virulence factors
How does AIP lead to expression of virulence genes
Gram-positive, staphylococcus aureus
AIP is encoded by agrD gene, AIP is cyclized by formation of thioacetone ring and exporter using AgrB (transmembrane transporter)
Mature AIP is bound by AgrC receptor and sensor histidine kinase of kin bacteria and phosphorylates the response-regulator AgrA.
AgrA-P activates transcription of RNAIII, which activates virulence genes
How does RNAIII activate virulence genes?
RNAIII is a small RNA molecule, that binds and inhibits the transcription regulator repressor of toxin (Rot)
RNAIII binding to rot, results in the derepression of virulence genes, allowing S. aureus to thrive in host
What molecule is used for intraspecies communication
Autoinducer-2, most common quorum sensing molecule, synthesized by the LuxS signal synthase
Some bacteria do not make Al-2 but can sense it
Chemical structure of AI2 differs between aquatic and terrestrial bacteria
