Quorum Sensing

This presentation elaborates on the process through which bacteria communicate with each other using signalling molecules which they can produce and receive.

1. QUORUM SENSING Presentation by: Areeba Nameen Menahil Khalid Alizay

2. Introduction ‘Quorum’ is a Latin word. It means the number of members of a group required to be present to transact business or carry out an activity legally

3. Quorum sensing is a process of bacterial cell-to-cell communication involving the production and detection of extracellular signaling molecules (autoinducers). “Autoinducers” contribute to the regulation of the expression of particular genes.

4. This is the intra communication system that is used by like bacteria to establish presence of their own kind. Each bacteria is able to send out a signals and receive one as well. This allows each individual bacteria to count how many other bacteria there are. Once the bacterium can assess that there is a proper amount of other bacteria present, it can simultaneously, along with the other bacteria emit a response such as virulence or bioluminescence

5. Discovery Quorum sensing was originally discovered in the luminescent bacterium Vibrio fischeri These bacteria exist as free-living cells or as symbionts in the light producing organ of an animal host, such as the Hawaiian bobtail squid. It was observed that liquid cultures of V.fischeri produced light only when large numbers of Bacteria were present.

6. History Nealson et al. (1970) – luminescence in the marine Gram-negative bacterium Vibrio fischeri controlled by self-produced chemical signal Eberhard et al . (1981) identified the V. fischeri autoinducer signal to be N -3-oxo-hexanoyl-L-homoserine lactone Engebrecht et al. (1983) cloned the genes for the signal generating enzyme, the signal receptor and the lux genes

7. Fuqua et al . (1994) introduced the term quorum sensing to describe cell-cell signaling in bacteria

8. Occurrence Within a single bacterial species as well as between diverse species. Quorum sensing allows both Gram-negative and Gram-positive bacteria to sense one another and to regulate a wide variety of physiological activities. 

9. Examples Name of the organism Aliivibrio fischeri Gram-negative Curvibacter sp Gram-negative Escherichia coli Gram-negative Salmonella enterica Gram-positive Pseudomonas aeruginosa Gram-positive Acinetobacter sp. Gram-positive Aeromonas sp. Gram-positive Yersinia Gram-positive Archaea Methanosaeta harundinacea 6Ac methanogenic archaeon Social insects Ants Social insect Honey bees

10. A brief overview of the process Quorum sensing can be divided into at least 4 steps: Production of small biochemical signal molecules by the bacterial cell Release of the signal molecules, either actively or passively, into the surrounding environment Recognition of the signal molecules by specific receptors once they exceed a threshold concentration, leading to Changes in gene regulation

11. A brief overview of the process in luminous bacteria

12. Molecules & Mechanism of Quorum Sensing

13. QUORUM SENSING MOLECULES 15 Each individual bacterium is capable of producing a signaling molecule (inducer) and each bacterium also has a receptor for the inducer. Signals lead to activation and suppression of certain genes leading to changes in metabolic activity, morphology, mobility, aggregation and association with other cells of same species or different species. Three main types of inducer molecules : 1) Acyl-homoserine lactones (AHLs) 2) Autoinducer peptides (AIPs) 3) Autoinducer-2 (AI-2)

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15. 17 A single bacterium has a genetic sequence that codes for an autoinducer, or a signaling molecule that will be released into the environment. This molecule can vary for different types of bacteria.

16. General Mechanisms

17. 19 Quorum sensing in Gram Positive Bacteria 01. Auto Inducer In Gram-Positive bacteria the autoinducers are Oligopeptides , short peptides typically 8-10 amino acids long. 02. Signal 03. Diffusion 04. Critical Level It uses these short peptides as a signal. Oligopeptides cannot diffuse in and out of bacteria like AHLs , but rather leave bacteria via specific exporters. When a critical level of oligopeptide is reached , the binding of the oligopeptide to it’s receptor starts phosphorylation cascade that activates DNA binding transcription regulatory proteins called response regulators.

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19. 21 Gram Positive Bacteria Reception 1: AIPs thread reaches receptor on bacterial cell. 2: AIPs then bind to membrane bound receptors such as AgrC (accessory genes regulator) Transduction 1: When AIPs bind to AgrC , the process of transduction begins . 2: The receptors then phosphorylated inside the cell . This results in formation of AgrA . 3: Transcribed DNA then make enzyme and protein specific for bacteria. Cellular response 1: It is the final step of the mechanism 2: AgrA protein begin to transcribe bacterial DNA. It creates more AIPs in a positive feedback loop .

20. 22 Example: Mechanism in Staphylococcus aureus

21. 23 Quorum sensing in Gram Negative Bacteria 01. Auto Inducer It uses acyl-homoserine lactones or AHL. 02. Signal 03. Diffusion 04. Critical Level It uses LUXI/LUXR as a signaling molecule. AHLs diffuse readily out of and into bacterial cells where they bind to AHL receptors in the cytoplasm of the bacteria. When a critical level of AHL is reached , the cytoplasmic autoinducer/receptor complex functions as a DNA-binding transcriptional activator.

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23. 25 Gram Negative Bacteria Reception 1: When AHLs reaches the surface of the receptor , then they bind to AI Synthase in cytoplasm of bacteria Transduction 1: AHLs are activated by the binding of AI Synthase. 2: As a result of binding , critical level of AHLs are attained. Cellular response 1: It is the final step of the mechanism. 2: AHLs then bind to AHL Receptor ,as a result cytoplasmic receptors function as DNA binding transcriptional activator. 3: The receptor Complex that are formed function as auto inducers.

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25. Interspecies communication Both gram-negative and gram-positive bacteria are able to cross talk by recognizing and processing autoinducing signaling molecules of other species. Beside AHL autoinducer molecules, another AI termed AI-2 was first discovered in the bioluminescent marine bacterium Vibrio harveyi . It was shown that AI-2 enables interspecies communication

26. Example: in gut & in Biofilms

27. It was also shown that pathogenic bacteria can interact with eukaryotic host cells, and vice versa, by utilizing each other’s autoinducing signals.

28. Quorum Quenching 30

29. Quorum Quenching Mechanisms that have evolved to interfere with bacterial cell-cell communication in processes are termed quorum quenching . Bacterial populations compete for limited resources, the ability to disrupt quorum sensing may give one bacterial species an advantage over another that relies on quorum sensing. Like wise, a host’s ability to interfere with bacterial cell-cell communication may be crucial in preventing colonization by pathogenic bacteria that use quorum sensing to coordinate virulence.

30. Quorum-quenching chemicals and enzymes Many quorum-quenching chemicals and enzymes have been identified. These include halogenated furanones from the seaweed Delisea pulchra, which are structural mimics of quorum-sensing signals. Enzymes such as AHL-lactonase, AHL-acylase and paraoxonases degrade AHLs. Synthetic AHL and AIP analogues have been developed to compete with quorum-sensing signals. In mammals, enzymes that inactivate AHLs have been found in serum and airway epithelia. Such natural quorum-quenching mechanisms may be used to develop a new generation of antimicrobials.

31. What does quorum sensing regulate?

32. Advantages Quorum Sensing 1. To optimize and regulate a variety of activities. 2. To communicate and to alter behavior in response to the presence of other bacteria. 3. Allow a population of bacteria to coordinate global behavior and thus act as a multi-cellular unit. 4. Enhance pathogenicity. 5. Evade host defense. 6. Improve overall survival.

33. Uses of Quorum Quenching Combat microbial resistance, pathogenesis, virulence etc. Decrease competition Prevention of bio-fouling Biocontrol of plant pathogens Prevention of biofilm formation on membranes in food industry and freshwater or wastewater treatment plants

34. Thank you for your time