BK - Biofilm Physiology and Quorum Sensing II Flashcards
What is biofouling, and why is it a problem? (2)
- Biofouling is the accumulation of microorganisms, plants, algae, or animals on wet surfaces.
- It is a major challenge for marine eukaryotes and can be highly detrimental to marine algae.
Why is Delisea pulchra not covered in biofilm? (3)
- Produces halogenated furanone compounds (secondary metabolites).
- These compounds exhibit anti-quorum sensing and antimicrobial properties.
- Structurally similar to HSL, allowing interference with QS signaling.
Name the compounds that block quorum sensing in Pseudomonas aeruginosa. (6)
- Patulin
- Penicillic acid
- 2-heptylthioacetyl-homoserine lactone
- 4-Nitropyridine-N-oxide
- C-30 and C-56 (experimental furanone compounds Delisea pulchra)
What is the function of furanone C-30? (3)
- Blocks induction of QS genes.
- Works in animal models.
- Promotes bacterial clearance.
What are AI-1 and AI-2 in quorum sensing?
AI-1: Used within species for communication (homoserine lactones with different derivatives).
AI-2: Involved in interspecies and inter-kingdom communication via the LuxS/LuxP system.
How is AI-2 produced?
- S-adenosylmethionine (SAM) → S-adenosylhomocysteine (via methyltransferases).
- S-adenosylhomocysteine → S-ribosylhomocysteine (via Pfs enzyme).
- S-ribosylhomocysteine → DPD (via LuxS enzyme).
- DPD → AI-2 (reacting with borate in some species).
e.g. E. coli O157, H. pylori
Why is boron important in quorum sensing? (3)
Essential for AI-2 formation in Vibrio (DPD + borate → AI-2):
- DPD to Pro-AI-2: DPD undergoes a ring closure reaction, forming Pro-AI-2.
- Pro-AI-2 to AI-2: Pro-AI-2 interacts with borate [B(OH)4-] to form the final AI-2 molecule.
Boron found in marine environments
Why are Vibrio quorum sensing genes called “lux” genes? (2)
- Vibrio species produce bioluminescence through quorum sensing.
- The lux operon is responsible for light production.
Examples: Used by the Hawaiian bobtail squid for camouflage.
What is the relationship between the Activated Methyl Cycle (AMC) and AI-2 production? (5)
- AMC Function: Generates S-adenosyl-methionine (SAM), the primary methyl donor, and recycles methionine by breaking down S-adenosyl-homocysteine (SAH). LuxS Enzyme Converts S-ribosyl-homocysteine (SRH) into 4,5-dihydroxy-2,3-pentadione (DPD), a precursor to AI-2.
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AI-2 Production: DPD is converted into AI-2 signal molecules, with variations based on bacterial species:
- Vibrionaceae: DPD reacts with borate to form S-THMF-borate.
- Enterobacteriaceae, Bacillaceae, etc: DPD spontaneously rearranges to form R-THMF (without boron).
- Alternative Pathway: Some bacteria (e.g., Alphaproteobacteria) use SAH hydrolase instead of LuxS to regenerate homocysteine.
How does AI-2 regulate quorum sensing in different bacteria?
Enterobacteriaceae (e.g., E. coli)
- AI-2 imported by Lsr transporter.
- Phosphorylated by LsrK
- Inactivates the LsrR repressor
- Activates lsr genes.
Vibrio (e.g., Vibrio cholerae)
- AI-2 binds to LuxP, initiating a dephosphorylation cascade involving LuxQ, LuxU, and LuxO
- ultimately derepressing LuxR, a transcriptional activator that activates the lux operon
- leading to bioluminescence.
How does Ruminococcus obeum restrict Vibrio cholerae gut colonization? (2)
- Uses AI-2 to downregulate V. cholerae virulence genes.
- Possible link between a healthy gut microbiome and pathogen resistance.
What is Burkholderia Diffusible Signal Factor (BDSF)? (2)
- A QS molecule used by Burkholderia cenocepacia and Pseudomonas aeruginosa.
- Regulates virulence, biofilm formation, and antibiotic tolerance.
How many QS systems does Burkholderia cenocepacia have in CF patients?
- Four QS systems: CepIR, CciIR, CepR2, and BDSF
- Some evidence suggests that B. cenocepacia may exacerbate Pseudomonas aeruginosa infections in CF patients.
Describe the quorum sensing systems that are present in Burkholderia cenocepacia? (4)
- AI-1 systems: Involving synthase and receptor pairs (CepIR and CciIR).
- BDSF-based system: Produced by the RpfFBC complex (a non-ribosomal peptide synthetase-like cluster, also called “ham”).
- CepI: Integral to biofilm formation, protease production, and virulence, interacting with both AHL-based systems (CepIR and CciIR) and the BDSF system.
How do DKPs influence Burkholderia cenocepacia quorum sensing?
- DKPs inhibit CepI in vitro.
- This inhibition reduces the bacterium’s ability to produce proteases, siderophores, and form biofilms.
- In C. elegans infection models, DKP treatment has been shown to prolong survival.
What is DSF, and what roles does it play in bacterial communication? (4)
- DSF is a cis-unsaturated fatty acid (cis-11-methyl-dodecenoic acid) first identified in Xanthomonas campestris.
- Produced as BDSF by B. cenocepacia and as CDA by P. aeruginosa.
- Regulates virulence, biofilm formation, and antibiotic tolerance.
- Acts as an autoinducer for biofilm dispersion and is involved in interspecies signaling.
What enzymes are involved in DSF synthesis, and why is substrate variation important? (3)
- RpfF: Functions as an enoyl CoA hydratase.
- RpfB: Acts as a long-chain fatty acyl CoA ligase.
- Different species utilize various substrates for DSF biosynthesis, and diverse sensor kinases detect DSF or BDSF, allowing species-specific responses.
How does DSF signaling regulate cyclic di-GMP in Xanthomonas campestris? (4)
- DSF signaling activates a cyclic di-GMP phosphodiesterase, reducing cyclic di-GMP levels.
Lower cyclic di-GMP levels lead to:
- Increased production of extracellular enzymes and EPS (exopolysaccharides).
- Inhibition of biofilm formation.
- DSF also enhances interactions between RpfG and GGDEF domain proteins that synthesize cyclic di-GMP, influencing bacterial motility without affecting extracel enzyme/EPS production or biofilm formation.
How do DSF family signals facilitate interspecies and inter-kingdom communication?
DSF and BDSF serve as communication molecules between different bacterial species and even between bacteria and fungi (e.g., Candida albicans).
What additional QS signals are produced by Pseudomonas aeruginosa, and what is their significance? (2)
- P. aeruginosa produces N-acyl homoserine lactones (N-AHLs), such as 3-oxo-dodecanoyl-homoserine lactone (oxo-C12-HSL).
- These molecules are important for inter-species/kingdom interactions, influencing both Candida albicans and B. cenocepacia
How do bacteria exit quorum sensing? (4)
- QS is energy-intensive.
- Need to exit during the post-quorum phase.
- DSF degradation systems (Use RpfB homologs) regulate QS signal turnover.
- Strains belonging to Bacillus, Paenibacillus, Microbacterium, Staphylococcus and Pseudomonas can rapidly degrade DSF
How is DSF signal turnover regulated in Xanthomonas campestris?
Pre-Quorum Sensing (Low DSF):
- DSF is low: RpfC and RpfF form a complex, keeping DSF levels down.
- c-di-GMP is high: This binds to Clp.
- Virulence is repressed: Clp-c-di-GMP inhibits rpfB transcription and virulence gene expression.
Quorum Sensing (High DSF):
- DSF activates RpfC: RpfC is phosphorylated.
- c-di-GMP is degraded: A phosphorylation cascade activates RpfG, which breaks down c-di-GMP.
- Virulence is activated: Freed Clp binds to the promoter of virulence genes (engXCA) and detaches from the rpfB promoter, permitting its expression.
Post-Quorum Sensing (Low DSF):
- RpfC deactivates: RpfC and RpfF complex reforms, RpfC dephosphorylates.
- c-di-GMP increases: RpfG deactivates, and c-di-GMP levels rise.
- Virulence is repressed again: Clp binds c-di-GMP and returns to the rpfB promoter, shutting down rpfB and virulence gene expression.
How do Gram-positive bacteria perform quorum sensing, and what role does the Agr system play? (8)
- Peptide-Based QS: Unlike Gram-negative bacteria that use HSLs, Gram-positive bacteria rely on small peptides.
- Agr Locus: Encodes a two-component system with divergent operons controlled by promoters P2 and P3.
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Operon P2 Genes: Includes AgrA, AgrB, AgrC, and AgrD.
- AgrD: Encodes the precursor of the autoinducing peptide (AIP).
- AgrB: Processes and secretes the AIP.
- Signal Transduction: At high cell density, AgrC (a membrane sensor) binds AIP, leading to AgrA phosphorylation and auto-induction via P2 and P3.
- Promoter P3: regulates the transcription of RNAIII
and δ hemolysin- An increase in RNAIII levels leads directly or
indirectly to a rise in numerous factors and induces the expression of the P2 promoter
- An increase in RNAIII levels leads directly or
What is the structure and diversity of AIPs in Gram-positive quorum sensing? (5)
- AIP Composition: Typically 7–9 amino acids long.
- Conserved Cysteine: All AIPs share a common central cysteine located 5 amino acids from the C-terminal.
- Macrocycle Formation: The C-terminal amino acid forms a catalytic thioester bond with the cysteine, creating a macrocycle.
- Exocyclic Tail: Usually composed of 2–4 amino acids (depending on the species).
- Polymorphism: AIPs are highly polymorphic and fall into four major groups based on their interaction with AgrC.
How do inhibitors of QS receptors function in Pseudomonas aeruginosa? (2)
- Target Receptors: Inhibitors block cytoplasmic receptors such as LasR, RhlR, and PqsR.
- Effect: This prevents the normal activation of virulence genes that is triggered by AHL and PQS signals.
How do inhibitors target the Agr system in Staphylococcus aureus? (2)
- Mechanism: Inhibitors use AIP mimics to block AgrC, the receptor for autoinducing peptides.
- Outcome: This prevents the natural AIP from binding and stops the subsequent activation of virulence genes.
What is the role of QseC in enterohemorrhagic Escherichia coli, and how is it inhibited?
QseC Function: Acts as a sensor kinase that detects AI-3, adrenaline, and noradrenaline.
Inhibitor: LED209 blocks QseC, preventing its autophosphorylation and downstream activation of virulence genes in multiple pathogens.
What interkingdom signals and anti-virulence compounds are involved in QS inhibition? (3)
- Interkingdom Signals: Include adrenaline, noradrenaline, and AI-3 analogues (along with signals like C-12 HSL).
Anti-virulence Compounds:
- Halogenated Furanones: Target QS in Pseudomonas aeruginosa.
- LED209: Blocks QseC and prevents virulence gene activation across several bacterial pathogens.
