Quorum sensing

Question 1

QS def

Answer 1

Bacterial intra- and inter-species communication mechanism.

Enables bacteria to regulate population behaviour in relaiton to populaiton density.

Question 2

Role of QS in virulence

Answer 2

Used in non- and pathogenic bacteria.
Must often reach critical density before causing disease.
Exceedin threshold > induction of VF expression

Question 3

Processes regulated by QS

Answer 3

Virulence
Biofilm formation
Antibiotic production sporulation
Competence
Bioluminescence

Question 4

QS in vibrio fischeri

Answer 4

Bioluminescence occurs only at high densities (in light organs of squids)

Question 5

QS process in gram-neg bacteria

Answer 5

Autoinducer (AHLs) produced by autoinducer synthase > secretion (membrane-diffusable) > interacts with intracellular transcriptional regulator LuxR > binding induces genetic transcription (lux-operon)

Specifity of AHL lies in legth and modifications of acyl side chain

Question 6

LuxR

Answer 6

Dimer. Ligand- and DNA-binding domains. INteracts with sigma70-RNA pol to acitvate gene expression.
LuxR superfamily of TF

Question 7

Activity curve

Answer 7

Sigmoidal acitvity curve, sharp threshold behaviour.
Small increase > ON-OFF.
Positive feed back loop AUtoinducer synthese is part of lux operon

Question 8

QS in gram-pos bacteria

Answer 8

Signals are oligopeptides autoinducers> bind to sensor kinases (two-component regulatory system)

Question 9

Interspecies communication

Answer 9

Autoinducer AI-2 is universal language.

Question 10

QS in Pseudomonas aeruginosa

Answer 10

Hierarchical QS circuit.
Two QS systems: first gene activaition and induction of second system > induces other set of virulence genes , biofilm formation!

Question 11

Bacteria lifestyles

Answer 11

Planctonic: single cells, floating/swimming in water/medium
Biofilms: surface-attached communities of microorg, cells are embedded in self-produced EZM, Single/multiple species

Many bacteria can switch. Biofilms preferred in nature.

Question 12

Biofilm advantages?

Answer 12

• Protection (from phagocytes/antibiotics/ab/amoebae/phages/biocides)
• Higher degree of metabolic diversity and flexibility
• Better adaption to sudden environmental changes
• Increased lateral gene transfer > increased genetic variability

Question 13

Infection related biofilms

Answer 13

Ass. with chronic infections. Increased resistance to phagocytosis and antibiotics. Typically monospecies.
Device- or tissue-related.
Dental plaque: multispecies.

Question 14

Biofilm structure

Answer 14

Bacteria embedded within self-produces matrix of extracellular polymeric substance (EPS)

EPS: mix of polysaccharides, proteins, nucleic acids
> mediates structural integrity
> physical barrier for some antibiotics

mushroom like projections

water and nutrient channels

Question 15

Biofilm life cycle

Answer 15

initial attachment > irreversible attachment > maturation I and II > dispersion

Question 16

Induction of biofilm formation - 2 signaling principles

Answer 16

1. QS
2. cyclic-di-GMP signaling (high > biofilm formation)

cdGMP interact with effector molecules > riboswitch (high > on)

Question 17

How to study biofilms

Answer 17

Giemsa staining

Laser scanning microscopy

Question 18

Persisters?

Answer 18

Subpoplations in biofilm showing resistance phenotypes (reduced growth, low metabolic activity)

Question 19

Treatment of biofilm infections

Answer 19

Idea: QS inhibition
> breakdown of biofilm structure, no selective pressure for development of resistance
> garlic extract, gingerol