L12 - Regulation & Environmental Interactions Flashcards
Bacteria mustadaptto changing environments to survive and successfully colonize hosts. Key aspects include:
- Adjusting tonew environments
- Evading host defenses through subversion or circumvention
- Ensuring long-term survival
How does regulation allow bacteria to control survival phenotypes?
Tailoring needs to a specific niche– particularly within thehost environment, where the immune system actively prevents infection.
What is niche-dependent behaviour and what are some examples of niches shifts.
- Example: Switching between attachment(to host cells) andavoidance (immune evasion).
- Transitioning betweenintracellular andextracellular lifestyles.
- encironment of host os constrictive
- microbe has sensed niche change e.g. water in gut
What are some ways in which bacteria interact with the host?
- Prevention of opsonization(avoiding immune detection).
- Toxin secretion– neutralizes host defenses.
- Disrupting mucosal integrity– facilitates infection.
- Modifying microbial recognition– alteringPAMPs(Pathogen-Associated Molecular Patterns) to evade detection.
- Chemokine interference– reduces immune response signaling.
How does infection occur and how do bacteria employ genetic strategies to enhance infecticity?
- Plasmids– carry virulence genes.
- Mobile genetic elements– includepathogenicity islands, which encode toxins and other factors.
How do bacteria sense their environment and regulate gene expression?
- regulatory networks (detect host signals to control gene expression)
- two-component systems (2CS) - sense environmental cues like magnesium levels temp and ph
- quorum sensing adjusts biofilm formation and virulence based on population density
What are the 2 types of responses from gene expression
Transient - reversible, non- mutational gene expression changes
Constitutive - permanent, multinational adaptations
What are the diff membrane-associated signalling systems to regulate gene expression ?
One component system, two component system, anti-sigma factors
Give definitions :
- signal
- sensor
- regulator
- regulon
- positive or negative control
- housekeeping vs virulence genes
- Signal– Environmental cue triggers gene regulation.
- Sensor– Protein detects the signal, changes conformation.
- Regulator– DNA-binding protein controls gene expression.
- Regulon– Group of genes regulated together.
- Positive or Negative Control– Genes can be activated or repressed.
- Housekeeping vs. Virulence Genes– Some genes are always on (housekeeping), while virulence genes are regulated based on need.
Describe bacterial regulons
Many ‘house keeping’ genes formed into networked hierarchies
Describe the environmental regulation of 2CS in regards to stimulus response mechanism and gene regulation
Stimulus response mechanism = signal transduction phosphoration transcription protein by histidine kinase sensor
Gene regulation - interaction with transcription protein (activator or repressor) effects on RNA polymerase sigma factors and DNA binding regulator
What is the location of regulatory protein and sensor?
Regulatory protein in cytoplasm and sensor in membrane
Histidine protein kinase causes what ? 2c can not perform regulators without what?
Conformational change - autophosphorylation and cannot perform regulators without phosphate
Describe the model for regulation of PhoP/Pho in enterobacteriales
High Mg2+ system is off -
Low Mg2+ system is on and activation is triggered, responds to host-derived SMPs leading to resistance mechanisms.
What are the diff components in PhoQ/PhoR?
PhoQ is the sensor kinase and detects low Mg2+ levels or presence of AMPs. Phosphorylation itself and transfers phosphate to PhoP
PhoP is the response regulator and it controls expression of multiple genes regulating LPS modification, AMP resistance and virulence factors
Summary:
Adaptive response to ___ extra cellular Mg2+ conc is required for ____. PhoP-PhoQ modifies ___ and controls resistance to ___ and ____. Reduced microbial virulence and increased in vivo immune ____
Low, pathogenesis , LPS, polymyxin B, AMP, evasion
What is a biofilm?
Structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface.
What is quorum sensing in terms of regulatory mechanism
Cell population density dependent regulation mediated via self generated extracellular signal molecules (autoinducrs)
How is biolfim used for bacterial self protection
Antibiotic only eradicated top most layer
What are the different low weight inducer molecules in gram positive vs gram negative bactera in primary QS
Positive = autoinducing peptides (AIPs)
Negative = acrylic-homoserine lactose’s (AHLs)
What is the structure of AHLs
- homoserine lectone ring
- Fatty acyl side chain(length and modifications vary among species)
What is the process of AHL QS signaling
- Synthesis– AHLs are synthesized byLuxI-type enzymes.
- Diffusion– AHLs diffusefreely across the bacterial membrane.
- Accumulation– As bacterial density increases, AHLsbuild up in the environment.
- Detection– When AHLs reach a threshold, they bind toLuxR-type regulators.
- Gene Activation– The LuxR-AHL complex binds to DNA andactivates or represses target genes.
What are the signal synthase and receptors in QS
LasRI or RhlRI
What does QS regulate
- biofilm formation, toxin production and virulence gene activation
What are the different components in quorum sensing
Signal synthase (produces the autoinducers)
Signal receptor (detects signal molecules)
Autoinducers (small molecules that modulate gene expression)
How is quorum sensing achieved in pseudomonas aeruginosa
- UsesLasRI & RhlRIsystems to regulate virulence.
- LuxR-type regulatorscontrol transcription.
- QS influences host-pathogen interactions:
- Induces pro-inflammatory cytokines.
- Enhances immune cell chemotaxis.
- Produces toxins (e.g., pyocyanin)that increase inflammation.
- Attenuates LPS-induced inflammationto promote infection.
