This document discusses quorum sensing, which is a communication mechanism between bacteria that allows processes like biofilm formation and virulence factor expression to be controlled. It defines quorum sensing and outlines three basic principles: bacteria produce signaling molecules called autoinducers, these molecules are detected by receptors, and detection leads to increased production of autoinducers. The document then discusses quorum sensing specifically in gram-positive and gram-negative bacteria, noting the different signaling molecules used. Finally, it provides one example of how engineering quorum sensing systems in E. coli bacteria allows them to sense and kill pathogenic Pseudomonas aeruginosa.

1. Submitted By:
Osama Alam
Department of Bio-Technology
University of Science & Technology, Bannu
September 2022

2. Quorum Sensing

3. Definition of Quorum Sensing;
• Quorum sensing (QS) is a
communication mechanism between
bacteria that allows specific processes
to be controlled,
• such as biofilm formation, virulence
factor expression, production of
secondary metabolites and stress
adaptation mechanisms such as
bacterial competition systems including
secretion systems (SS).

4. Basic Principles;
 QS systems depend on three basic
principles.
 First, the members of the community
produce AIs, which are the signaling
molecules. At low cell density (LCD),
AIs diffuse away, and, therefore, are
present at concentrations below the
threshold required for detection. At
high cell density (HCD), the
cumulative production of AIs leads to
a local high concentration, enabling
detection and response (Kaplan and
Greenberg 1985).
 Second, AIs are detected by
receptors that exist in the
cytoplasm or in the membrane.
Third, in addition to activating
expression of genes necessary for
cooperative behaviors, detection
of AIs results in activation of AI
production (Novick et al. 1995;
Seed et al. 1995).

5. Quorum Sensing in Gram Positive Bacteria
 Gram-positive bacteria use
peptides, called autoinducing
peptides (AIPs), as signaling
molecules.
 Once produced in the cell, AIPs
are processed and secreted. When
the extracellular concentration of
the AIP is high, which occurs at
HCD, it binds to a cognate
membrane-bound two-component
histidine kinase receptor.
 Usually, binding activates the
receptor’s kinase activity, it
autophosphorylates, and passes
phosphate to a cognate
cytoplasmic response regulator.
 The phosphorylated response
regulator activates transcription
of the genes in the QS regulon

6. Qs in Gram Negative Bacteria
o Gram-negative bacteria
communicate using small
molecules as AIs.
o These are either acyl-
homoserine lactones (AHLs) or
other molecules whose
production depends on S-
adenosylmethionine (SAM) as
a substrate (Wei et al. 2011).
AIs are produced in the cell
and freely diffuse across the
inner and outer membranes.
o When the concentration of AIs is
sufficiently high, which occurs at
HCD, they bind cytoplasmic
receptors that are transcription
factors. The AI-bound receptors
regulate expression of the genes
in the QS regulon

8. Use in biotechnology;
Sensing And killing in bacteria:
They engineered Qs system in E.coli bacteria.
 i.e Qs promoter (plux R)
 Pseudomonas aeroginose is a pathogenic bacteria secrets
N-3-oxyhexonyl
This chemical is sensed by E coli and produce Lysin E7
protien and Pyisin -5 bacteriocin.
This hemical kill the P aeroginose.