Regulation of Bacterial Processes and Environmental Interactions

Question 1

Describe how quorum sensing and two-component regulatory systems allow cells to adapt to fluctuating conditions.

quiz

Answer 1

Define the condition, if it is in vivo
Two component regulatory systems
-Discuss the PhoPQ system in Salmonella Typhimurium
-Include SPI-2 induction of T3SS release of effectors, LPS
modification and intramacrophage survival
Quorum sensing systems
-Discuss LasRI and RhlRI system in Pseudomonas aeruginosa
-Effect of the production of pyocyanin, exotoxin A
Can you think of more examples?

Question 2

How do efflux pumps contribute to pathogenesis?

quiz

Answer 2

-Using the example of AcrAB-TolC system which is also a Type I secretion system involved in the extrusion of antibiotics and host defense factors
-Functional in both environmental and in vivo conditions
-Subject to regulation by multiple regulatory factors which are important for survival

Question 3

How are bacterial virulence factors controlled?

quuiz

Answer 3

-Responsive, conditional or constitutive
-Provide examples T3SS expression-effector release QS systems, LPS modifications

Question 4

How does bacterial gene regulation control virulence?

Answer 4

Environmental signals influence gene regulation, which can promote virulence factors. For example, when enterobacteria get eaten by a macrophage, the Mg and Ca levels drop which induces PhoP/PhoQ pathway which produces LPS.

LPS is virlence facotr, PhoP/PhoQ is a two component system

Question 5

How do the gene regulatory circuits work in concert to facilitate colonisation and pathogenesis?

Answer 5

PhoP-PhoQ and PmrA-PmrB work in conjunction and act on the same regulon/overlapping regulons to modify LPS which leads to antimicrobial peptide resistance

Question 6

How is gene expression managed at a community level (biofilm) to ensure in vivo survival?

Answer 6

Quorum sensing, and auto-inducer production
eg. AIP - gram pos and AHL- gram neg
LasR/Rh1r are set off when biofilms detect HSL which is an autoinducer (which makes toxins like pyomyacin which damages tissues)

Autoinducers are produced by all bacteria, and if theres a high conc of bacteriial cells then the conc of auto inducers is high enough to generate genetic cascade

Essentially, signals that biofilm is big enough to start becoming pathogenic

Question 7

Why is sensing the environment relevant to bacterial colonisation and infection?

Answer 7

Change in conditions allows it to control what genes are expressed which allows it to survive in those conditions and optomize energy usage
Eg PhoP-PhoQ are activated when Mg is low

Question 8

How can bacteria utilise these genetic systems to evade the immune response or cause pathogenesis?

Answer 8

Can use complement systems to produce toxins/set off genetic cascades

Question 9

What are three things that two component regulatory systems do to contribute to pathogenicity?

Answer 9

1. Trigger toxin production
2. Trigger cellular damage
3. Lipopolysaccaride modification