1. Semantics of Quorum Sensing and Quorum Quenching
Saima Naureen
07-arid-1191
Ph.D Zoology

2. Contents Introduction Signalling molecules Mechanism Quorum Quenching
Biofilms
Applications
Advantages
Conclusion and Future perspective
References

3. Introduction. Quorum Sensing
Cell to cell conversation
A signaling mechanism in microorganisms
Control gene expression
Cell density dependent
Example:
Bacteria and some social insects (ants and honey bees etc.)

4. History
Research into AHL based quorum sensing started in the late 1960s.
The marine bioluminescent bacteria Vibrio fischeri was being grown in liquid cultures and produced light only when large numbers of bacteria were present (Greenberg, 1967).
culture media contained an inhibitor of luminescence, which was removed by the bacteria when large numbers were present (Kempner & Hanson, 1968).
 It was later shown that the luminescence was initiated by the accumulation of an activator molecule or "autoinducer" (Nealson et al, 1970, Eberhard, 1972).

5. Cont….
Vibrio fischeri, lives as a mutualistic symbiont in the photophore (or light-producing organ) of the Hawaiian bobtail squid.
free-living (or planktonic) the autoinducer is at low conc., so no luminesence.
highly concentrated in the photophore (about 1011 cells/ml) transcription of luciferase is induced, leading to bioluminescence.
Luciferase/;????

6. Decision Making Process
Quorum sensing can function as a decision-making process in any decentralized system, as long as individual components have:
(a) a means of assessing the number of other components they interact with
(b) a standard response once a threshold number of components is detected.

7. Why do bacteria talk to each other?
Biofilm????? Virulence?///

8. Where Quorum sensing occurs?
Within and between
bacterial species
Between prokaryotes and
their eukaryotic host
Animal
Plant

9. Cross Talk Cross talk Interspecies communication
Cross talk has implications in many areas of microbiology
Antibiotic resistance
Virulence
Biofilms (mixed species populations)

10. Signaling Molecules Three types of molecules:
Oligopeptides Autoincduer (AIPs)
Acyl-homoserine lactones (AHLs)
Autoinducer-2 (AI-2)

11. Table: 1.1 Class Signaling Molecules Strains Gram- Bacteria AHLs
V. fisheri
V. harveyi
Gram + Bacteria
AIPs
B.subtilis,
S. aureuas
Gram + Bacteria and
Gram -Bacteria
Al-2
E. coli

12. Oligopeptide Autoinducer
These are small peptides.
Regulates competence and sporulation gene expressions

13. Mechanism of Oligopeptide Autoinducers
The precursor peptide is modified, processed and an ATP-binding cassette (ABC) exporter complex secretes the mature Oligopeptides-autoinducer.
At high cell density the autoinducer is detected by a two-component signal transduction system. Specifically, the sensor kinase protein recognizes the autoinducer and subsequently autophosphorylates at a conserved histidine residue (H).
The phosphoryl group is transferred to a cognate response regulator protein, and this protein is phosphorylated on a conserved aspartate residue (D).
The phosphorylated response regulator binds to specific target promoters to modulate the expression of quorum sensing regulated genes.

14. Mechanism of AIPs

15. Acyl-homoserine lactones (AHLs)
These are of several types depending on their length of acyl side chain.
Able to diffuse through membrane.
Involve virulence and biofilm formation.

16. Mechanism of Acylhomoserine Lactones AI-1
These are synthesized by an autoinducer synthase LuxI and recognized by a autoinducer receptor/DNA binding transcriptional activator protein LuxR.
LuxR binds to the promoter region and initiate transcription of target gene.
There is a low likelihood of a bacterium detecting its own secreted inducer

17. Mechanism of AHLs

18. Autoinducer-2 (AI-2)
Involve in interspecies communication among bacteria
AI-2 is synthesized by the reaction of 1-deoxy-3-dehydro-D-ribulose with boric acid. Chemically these are furanosyl borate diester

19. Mechanism of Autoinducer-2
Al-2 are synthesized by LuxS and sensed by Lsr transporter cassette (ACDB), then phosphoryrated by kinase LsrK.
The Phospho-Al-2 binds with LsrR and transcription of the lsr genes is initiated result in (lsrACBDFG) expression

20. Mechanism of Al-2

21. Hybrid Quorum Sensing Circuit
The hybrid quorum sensing circuit of V. harveyi. Elements characteristic of both Gram-negative and Gram-positive bacterial quorum sensing systems are combined to make up the V. harveyi circuit.

22. Mechanism of Hybrid Quorum Sensing Circuit
An acyl-HSL autoinducer (AI-1, green pentagons) is produced by the activity of LuxLM.
A second autoinducer (AI-2, red pentagons) is synthesized by the enzyme LuxS. AI-2 is proposed to be a furanone.
Both autoinducers accumulate as a function of cell density.
The sensor for AI-1 is LuxN and two proteins, LuxP and LuxQ function together to detect AI-2.

23. Cont…
LuxN and LuxQ are hybrid sensor kinase/regulator protein that transduce information to a shared integrator protein called LuxU.
Lux U send the signal to the response regulator protein LuxO.
LuxO controls the transcription of a putative repressor protein (denoted X) and a transcriptional activator protein called LuxR is also required for expression of the luciferase structure operon (lux CDABE).

24. Mechanism of hybrid quorum sensing

26. Quorum Quenching 1.Bacterial Virulence:
QSI is a potential method for inhibition of bacterial virulence both
In-vitro
In-vivo

27. Cont…
Recent research into quorum sensing systems has produced compounds that can disrupt the bacteria's ability to communicate, thereby disabling or diminishing the bacteria's ability to become pathogenic.
Therefore, the body is not compromised by cell damage, inflammation, toxicity, or other detrimental effects of the bacteria.
This gives the body time to eradicate the bacteria naturally through normal immune system functions.

28. 2. Anti-biotic resistance
Now a days most of bacteria are antibiotic resistant
Penicillin resistant bacteria developed in 1942, just after 2 years of its introduction
Antibiotic sensitive bacteria
Antibiotic resistant bacteria

29. Strategies for quorum sensing inhibition
3 strategies can be applied
Targeting signal
Generation
Targeting AHL signal
dissemination
Targeting the signal
Receptor
Signal precursor
Signal
Signal
Signal
Signal receptor
Signal receptor
Signal receptor

30. Conversation between bacteria
To Talk? Or Not To Talk?
Quorum Quenching
Quorum sensing
QS Inhibitors
Autoinducers
Quorum quenching???
Natural Synthetic AHL QSI QSI QSI degradation system
Regulate QS-controlled phenotypes
Block Quorum Sensing Pathway

31. Applications QS research has many potential applications:
Models to understand biology of sociality
Understanding bacteria
To develop new medicines to treat devastating bacterial infection like
Cystic fibrosis
Otitis Media
Bacteria Endocarditis etc.

32. Biofilms Bacteria use quorum sensing in biofilm formation.
A structured community of bacterial
cells enclosed in self-produced
polymeric matrix.
They are protective mode of growth
that allows survival in hostile
environment.
Bacteria in the biofilms are inherently
resistant to killing.

33. Why research on Biofilms?
Due to morphology of biofilms, bacteria capable of forming them are highly resistant to Antibiotics, making treatment difficult.

34. Advantages of Anti-Quorum Sensing
The advantage of the anti-quorum sensing approach to controlling infection is that there are few evolutionary forces that select for resistance—there is little in the process that would create resistant strains.
Since the compounds kill none of the bacteria, any resistant mutations must compete with living, non-resistant individuals.
In other words, there is no survival advantage to the resistant mutations, and natural selection does not come into play. Resistant strains will be unlikely to occur.

35. Cont…
Next to the potential antimicrobial functionality, quorum-sensing molecules, especially the peptides, are investigated for their use in other therapeutic domains as well, including immunology and oncology.
This hypothesis is based on
(1) the recent evidence of prokaryote–eukaryote signaling by the use of quorum-sensing signaling molecules
(2) the apoptotic phenomenon seen in bacteria
(3) the clear similarities between the bacterial quorum-sensing mechanisms and the metastatic process tumor cells initiate
(4) the multiple receptor targeting and
(5) the possibility of pharmacologic manipulation of peptides, resulting in increased receptor targeting.

36. Conclusions and future perspectives
QS inhibitors have provided evidence of alternative method for fighting bacterial infections.
QS inhibitors can be isolated from the huge natural pool of chemicals.
unsuitable compounds lead to lack in selection of human compatible QS inhibitors.
Further studies are needed on QS gene expression
QS inhibitors, may replace the antibiotics.

37. Abbreviations DPD: (4,5-dihydroxy-2,3-pentanedione)
ABC: (ATP binding cassette)
AI: Autoinducing protein
AHLs: N-acylhomoserine lactones
H: Histidine
D: Aspartate

38. References
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Thomas, G. Platt. & Clay Fuqua. (2010). Whats in a name? The semantics of quorum Sensing. 18(9): Microbiol
Antunes, L. C. & Ferreira, R. B. (2009). Intercellular communication in bacteria. Crit Rev Microbiol 35, 69–80.
Bendiak, G. N. & Ratjen, F. (2009). The approach to Pseudomonas aeruginosa in cystic fibrosis. Semin Respir Crit Care Med 30, 587–595.
Otto, M., Sussmuth, R., Jung, G. & Gotz, F. (1998). Structure of the pheromone peptide of the Staphylococcus epidermidis agr system. FEBS Lett 424, 89–94.
Smith, D., Wang, J. H., Swatton, J. E., Davenport, P., Price, B., Mikkelsen, H., Stickland, H., Nishikawa, K., Gardiol, N. & other authors (2006). Variations on a theme: diverse N-acyl homoserine lactone-mediated quorum sensing mechanisms in Gram-negative bacteria. Sci Prog 89, 167–211.