Difference Between Quorum Sensing and Quorum Quenching

The key difference between quorum sensing and quorum quenching is that quorum sensing is a gene expression regulation mechanism utilized by bacteria to communicate with each other and sense their cell population densities, while quorum quenching is a mechanism of bacteria that works against the quorum sensing and stops the virulence gene expression.

Bacteria utilize different mechanisms to communicate with each other. These communication mechanisms help them to feel the population densities, and to regulate many of their physiological processes. Quorum sensing is one such mechanism utilized heavily by bacteria. Quorum sensing not only facilitates communication and sensing the population densities, but it also plays a big role in maintaining the pathogenicity of bacteria towards other hosts such as humans. However, quorum sensing mechanisms are problematic in controlling bacterial infections. As a solution, quorum quenching can be used. Quorum quenching interferes the quorum sensing of bacteria and shuts down the expression of the pathogenic genes.

CONTENTS

1. Overview and Key Difference
2. What is Quorum Sensing 
3. What is Quorum Quenching
4. Similarities Between Quorum Sensing and Quorum Quenching
5. Side by Side Comparison – Quorum Sensing vs Quorum Quenching in Tabular Form
6. Summary

What is Quorum Sensing?

Quorum sensing is a gene regulation mechanism used by bacteria. They utilize this mechanism to communicate with bacterial cells and sense their own population density. They produce and secrete small molecules known as autoinducers to sense the population density. Using this method, they regulate the expression of virulence genes. Moreover, autoinducers are small diffusible signalling molecules, mainly N-acyl-homoserine lactones (AHL). They trigger the expression of virulence genes.

Figure 01: Quorum Sensing

Quorum sensing is important for many physiological activities of bacteria. Quorum sensing molecules induce processes such as symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, nitrogen fixation and biofilm formation, etc.

Furthermore, quorum sensing is common in both gram-negative and gram-positive bacteria. However, they secrete different molecules as autoinducers. Gram-negative bacteria mediate quorum sensing through acylated homoserine lactones while gram-positive bacteria mediate it through processed oligo-peptides.

What is Quorum Quenching?

Quorum quenching is a natural mechanism of bacteria that works against the quorum sensing mechanism of bacteria. When quorum sensing helps bacteria to express virulence genes, quorum quenching inhibits it. Thus, quorum quenching is a mechanism that shuts down the virulence gene expression in pathogenic bacteria. In quorum quenching, bacteria produce enzymes and chemical inhibitors to degrade quorum sensing molecules. Upon degradation of autoinducers, bacteria lose their quorum sensing ability. Hence, quorum quenching disrupts the ability of a pathogen to sense its cell density and disable or diminish the capability of triggering the virulent expression.

Figure 02: Quorum Quenching

Quorum quenching stops quorum sensing by several methods. It inactivates signalling enzymes or introduces molecules that mimic signalling molecules and blocks their receptors. Furthermore, quenching enzymes degrade signalling molecules or modify quorum sensing signals.

Since quorum quenching is a natural mechanism, it can be developed as an approach to prevent microbial diseases. Bacterial communication is an important aspect of bacterial infections. Hence, quorum quenching will be a promising solution for interfering bacterial communication, thereby preventing bacterial diseases. Thus, quorum quenching can be simply defined as a form of anti-virulence.

What are the Similarities Between Quorum Sensing and Quorum Quenching?

• Both these mechanisms are seen mainly in bacteria.
• They are also natural mechanisms occurring in bacteria.
• Moreover, both processes produce enzymes, chemicals, etc. to mediate the processes.

What is the Difference Between Quorum Sensing and Quorum Quenching?

Quorum sensing is a process that bacteria use to communicate with each other and sense their population densities. In contrast, quorum quenching is a process that bacteria use to disrupt quorum sensing. So, this is the key difference between quorum sensing and quorum quenching.

Moreover, another significant difference between quorum sensing and quorum quenching is that the bacteria secrete autoinducers or quorum sensing signals in quorum sensing, while bacteria produce enzymes and quorum sensing inhibitors in quorum quenching.

Below infographic provides more comparisons with regards to the difference between quorum sensing and quorum quenching.

Summary – Quorum Sensing vs Quorum Quenching

Quorum sensing and quorum quenching are two natural mechanisms taking place in bacteria. Quorum sensing facilitates the communication between bacteria and sensing their population densities. It occurs via small molecules called autoinducers. It is an important process for bacteria since it aids in symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, nitrogen fixation and biofilm formation, etc. Meanwhile, quorum quenching works against quorum sensing. It disrupts quorum sensing and shuts down virulence gene expression. Hence, it is an anti-virulence mechanism. So, this is the summary of the difference between quorum sensing and quorum quenching.

Reference:

1. Miller, M B, and B L Bassler. “Quorum Sensing in Bacteria.” Annual Review of Microbiology, U.S. National Library of Medicine, 2001, Available here.
2. Chen, Fang, et al. “Quorum Quenching Enzymes and Their Application in Degrading Signal Molecules to Block Quorum Sensing-Dependent Infection.” International Journal of Molecular Sciences, MDPI, 26 Aug. 2013, Available here.
3. Catherine, et al. “Quorum Quenching: Role in Nature and Applied Developments.” OUP Academic, Oxford University Press, 1 Oct. 2015, Available here.

Image Courtesy:

1. “Quorum quenching” By BQUB13 Cizquierdo – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Quorum sensing of Gram Negative cell” By Gluckma2 – own work, (CC BY-SA 4.0) via Commons Wikimedia

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