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Quorum Sensing in Bacteria
- Quorum sensing in bacteria Quorum.
- It is a Latin word that means a group of members carries out an activity legally.
- Quorum sensing is a mechanism of cell to cell signaling or density sensing in micro-organisms.
Characteristics for quorum sensing
- For the bacteria to use quorum sensing constitutively, they must possess three characteristics:
- To secrete a signaling molecule, an auto-inducer.
- Detect the change in concentration of signaling molecules.
- And to regulate gene transcription as a response.
Image Source: Springer
Components in Bacteria
Showing quorum sensing requires these things.
- Signaling molecules called auto-inducers.
- A receptor that can specifically detect the signaling molecule.
- A universal autoinducer AI-2.
Autoinducers in gram-negative bacteria
- The autoinducers are typically molecules called acyl-homoserine lactones (AHLs).
Autoinducers in gram-positive bacteria
- The autoinducers are oligopeptides, short peptides typically 8 to 10 amino acids long.
- Some diffusible molecules secreted by bacterial cells which when cell density becomes sufficient can be detected by other cells in the population and which contribute to the regulation of expression of particular genes.
- Production and release of signaling molecules.
- The diffusion of AL molecule at low cell density leaves the QS circuit inactive.
- Activation of the QS circuit by AL at higher concentration due to higher cell density
- Transcriptional activation of downregulating genes by AL receptor complex or other activated signals molecules
- Activation of virulence, biofilm formation, sporulation, competence, and antibiotic production.
- Low bacterial density low signal molecules concentration
- High bacterial density high signal molecules concentration
- Gram-positive bacteria communicate using modified oligopeptides as signals and “two components “type membrane-bound sensor histidine kinase as receptors.
- Because peptides are impermeable to biological membranes, secretion of quorum- sensing peptides is usually mediated by specialized transporters
- Signaling is mediated by phosphorylation cascade that influences the activity of a DNA-binding transcriptional regulatory protein termed a response regulator.
Example: Bacillus spp.
LuxI-type enzymes catalyze the formation of species-specific HSLs which are detected by luxR- type transcriptional regulators.
- Quorum sensing allows bacteria to communicate within and between the species. This notion arose with the discovery and study of auto-inducer AI-2
- LuxS encoding the AI-2 synthase is present in roughly half of all sequenced bacterial genomes.
- AI-2 production has been verified in a large number of these species.
- AI-2 controls the gene expression in a variety of bacteria.
- Together these findings have led to the hypothesis that bacteria use AI-2 to communicate between species.
Institutes working on quorum sensing and quenching
- The University of Nottingham.
- National institute of General Medical Sciences.
- Institute of Technology Bombay, Powai Mumbai.
- Department of Biotechnology, University of Sargodha.
- Department of Microbiology & Molecular Genetics, Quaid-e-Azam Campus, University of the Punjab, Lahore, Pakistan.
- National University of Sciences and Technology(NUST) Islamabad, Pakistan.
- Department of Plant Pathology, University of Agriculture Faisalabad(UAF).
Conclusions and future perspectives
- Quorum sensing inhibitors have provided evidence of the alternative methods for fighting bacterial infections.
- Most compounds are unsuitable for human use.
- Further research in this area and isolation of proper Quorum sensing inhibitors, may replace the antibiotics.
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