Cell interactionsquorum sensing
Microbiology BIOL333
Hiba Al-Kurdi - Syntia Diallo - Majd - Hasan Abbas
Instructor: Dr. Rana Chehade
Fall Semester 2022-2023
Recalling Bacterial Cells
•
Bacteria are single celled microscopic
organisms containing a single DNA and only
few genetic information that encode all their
traits.
•
They multiply by growing and dividing
through binary fission.
)
But…
How could
they do
that?!
●
01
Bacterial interaction
Definition & How do
they occur
 Bacteria are social organisms that interact extensively within and between species
all while responding to external stimuli from their environments in order to
cooperatively function. Indeed, the ability to perceive neighbouring cells and the
environment as well is usually reflected in the content of the bacterial genomes.
 These interactions are done in several different ways using chemical signal
molecules which they release into the environment. These molecules travel from
cell to cell to finally bind on bacterial surface receptors where this allows them to
detect and respond to the build up of the molecules.
 Knowing the different kinds of interactions is highly important for us as they could
lead us to new strategies for prevention or treatments for bacterial infections.
type of interactions
Commensali
+/0
The host isn’t
harmed
Protocooperatio
n (Synergism)
+/+
Not obligatory
mutual benefits
Mutualism +/Mutual benefits
from host
Predation -/+
Predator/prey
relationship
Parasitism-/+
The host is
harmed
Amensali 0/One organism has
a negative effect on
the other
Competition -/2 microorganisms
try to get to
another by
competing
Mutualism
Predation
Commensalism
Protocooperation
Parasitism
Competition
Amensalism
Bacterial interactions under
stress
The bacterial stress response enables bacteria to survive
adverse and fluctuating conditions in their immediate
surroundings.
The most important bacterial stress responses include :
1- The envelope stress response
2- The heat shock response
3- The cold shock response
4- The general stress response.
Why Do Bacteria
Communicate with
Each Other?
When an infection is signaled, they form biofilms, dense
structures with powers of resistance against both antibiotics
and the body’s immune defense system.
At the same time, they become more aggressive and
increase their mobility.
bacteria are able to cooperate to efficiently infect a host
and make their new home more tolerable. They achieve
this in several ways.
How Do Bacteria Interact with
Each Other Using Quorum Sensing
 Bacteria talk to each other using N-AcylHomoserine Lactones (AHLs)
as quorum sensing (QS) signals. This signaling allows the bacteria to
control gene expression of virulence factors and biofilms once a
critical density has been achieved. This phenomenon, quorum
sensing, is important when an infection propagates.
 When an infection is signaled, more and more bacteria gather
at the site of the attack (a wound, for example). When there is a
critical mass, the bacteria start acting like multicellular
organisms. They form biofilms, dense structures with powers of
resistance against both antibiotics and the body’s immune
defense system. At the same time, they become more
aggressive and increase their mobility. All these changes are
triggered when the communication molecules (short fatty
acids, AHLs) bind to receptors inside the bacterial cells,
triggering gene expression changes.
 Once enough bacterial cells are present and producing a high enough
level of autoinducer, the bacteria respond to the message and start to
work as a team.
 Together, they coordinate the production of different molecules and
even coordinate how the cells move. This teamwork is what ultimately
allows bacteria to survive in various environments.
 Even though quorum sensing is beneficial for bacteria, it can often be
very bad for our health. By using quorum sensing, bacteria are able to
cooperate to efficiently infect a host and
make their new home more tolerable.
They achieve this in several ways:
- First, bacteria use quorum sensing to produce molecules, known as
virulence factors, which are beneficial to them.
- When enough of these bacteria colonize a human host, they coordinate the
production of a molecule called hemolysin. This molecule helps the
bacteria to acquire essential nutrients and compounds important for their
survival.
- Sounds harmless, right? Unfortunately, they do this by bursting (or lysing)
our red blood cells allowing the bacteria to take up and use the nutrients
inside. Sometimes, this blood cell destruction is not widespread enough to
be particularly problematic for the host. However, in other cases,
hemolysins can cause severe damage in lung tissue during diseases like
pneumonia.
Advantages of Bacterial
Interactions
•
Microbial interactions are crucial for a successful establishment and
maintenance of a microbial population.
•
The result of this multiple interaction is frequently related to pathogenic
or beneficial effect to a host.
•
In humans, for example, the microbial community plays an important
role in protection against diseases, caused by microbial pathogens or
physiological disturbances.
•
Soils microbial communities also play a major role in protecting plants
from diseases and abiotic stresses1 or increasing nutrient uptake.
Are Bacteria Multilingual?
●
Bacteria can behave either as individual single-celled
organisms or as multicellular populations.
●
Bacteria is also a multilingual champion, possessing
secondary molecules which helps them to contact
neighbouring bacteria and in unison.
02
Quorum sensing
The less we are, the less we can do!
What is Quorum Sensing?
Quorum sensing (QS) is a bacterial cell–cell
communication process that involves the production,
detection, and response to extracellular signaling
molecules called autoinducers (AIs).
How does it occur
Quorum sensing can be divided into at least 4 steps:
(1)
Production of small biochemical signal molecules by
the bacterial cell.
(2)
Release of the signal molecules, either actively or
passively, into the surrounding environment.
(3)
Recognition of the signal molecules by specific
receptors once they exceed a threshold concentration.
(4)
Gene expression regulation.
Quorum Sensing in Gram +ve:
●
●
●
Oligopeptides serve as the signaling molecules. They are secreted
and then are either detected at the bacterial surface by twocomponent systems or reinternalized via an oligopeptide transport
system.
Because peptides are impermeable to biological membranes,
secretion of quorum- sensing peptides is usually mediated by
specialized transporters.
In the latter case, imported peptides interact with cognate regulators
(phosphatases or transcriptional regulators) that modulate the
expression of target genes. These regulators help control crucial
functions such as virulence, persistence, conjugation and
competence and have been reported in bacilli, enterococci and
streptococci.
●
●
In this issue of Molecular Microbiology, Hoover et al. (2015)
highlight the group's importance: they have identified a new
family of regulators, Tprs (Transcription factor regulated by a Phr
peptide), which work with internalized Phr-like peptides. Hoover et
al. (2015) have provided a new insight: an environmental molecule,
glucose, can inhibit expression of the Phr-like peptide gene via
catabolic repression.
This previously undescribed regulatory pathway, controlling the
production of a bacteriocin, might influence Streptococcus
pneumonia's fitness in the nasopharynx, where galactose is
present.
Quorum Sensing in Gram –ve:
•
•
•
Acyl-HSL quorum sensing is commonly found in Gramnegative bacteria that interact with plant and animal hosts.
Quorum sensing was first discovered to control the
luminescence of Vibrio Fischeri, a bacterium that forms a
mutualistic light organ symbiosis with certain marine
animals.
Thus acyl-HSL quorum sensing appears as a common theme
in the interaction of several different bacterial species with
eukaryotic hosts.
The Difference Between Them:
Both Gram-negative and Gram-positive bacteria use this type of
communication, though the signal molecules (auto-inducers) used
by them differ between both groups:
 Gram-negative bacteria use predominantly N-acyl homoserine
lactone (AHL) molecules (autoinducer-1, AI-1).
 While Gram-positive bacteria use mainly peptides (autoinducer
peptides, AIP or quorum sensing peptides).
 These quorum sensing molecules are not only involved in the
inter-microbial communication but can also possibly crosstalk
directly or indirectly with their host.
Types of Quorum Sensing
Quorum sensing systems in bacteria are generally divided into
at least 3 classes:
LuxI/LuxR
type:
Quorum sensing in
gram -ve bacteria
which uses AcylHomoserine Lactones
(AHL) as signal
molecules.
Oligopeptide
2 component
type:
Quorum sensing in
gram +ve bacteria
which uses small
peptides as signal
molecules.
LuxS encoded
autoinducer-2 (AI-2)
type:
Quorum sensing in
both gram +ve and
gram -ve bacteria.
This has been seen
in V. harveyi and E
coli.
LuxI/LuxR Type:
 An intracellular autoinducer synthase (LuxI) synthesizes AHL
signal molecules by catalyzing a reaction between Sadenosylmethionine (SAM) and an acyl carrier protein.
 Due to the small size and lipophilicity of AHL autoinducers,
they readily pass the cell membrane by means of passive
diffusion.
 If the concentration of AHL is sufficiently high, the AHL
autoinducer binds to the intracellular LuxR protein and
provokes the LuxR DNA binding domain to reveal.
 Subsequently, the LuxR protein binds to DNA, causing
activation of target gene transcription.
Oligopeptide 2
Component Type
 These peptides are synthesized by ribosomes as precursor peptides and
undergo posttranslational modifications during excretion to become activated
and stabilized.
 In general, the secretion of the AIP is facilitated by a membrane associated
ATP-binding cassette (ABC) transporter.
 As the density increases, the AIPs accumulate in the environment. When a
certain threshold level is reached, binding of an AIP to a receptor initiates
activation of the receptor kinase by phosphorylation on a conserved histidine
residue.
 Subsequently, the activated receptor kinase transfers the phosphoryl group to
a conserved aspartate residue of the intracellular response regulator, which in
turn will be activated.
 The activated response regulator influences the transcription of target genes,
including the AIP genes, genes for the receptor kinase and response regulator,
and genes for the ABC transporter.
LuxS Encoded
Autoinducer 2 Type
 AI-2 contributes to gene regulation for E. coli including regulation of
virulence gene expression, type III secretion, flagellar synthesis,
motility, and chemotaxis.
 At high cell density, AI-2 can bind to cellular receptors that
subsequently regulate protein production and biofilm formation.
 During the mid-to-late exponential growth phase of bacteria, AI-2
reaches its maximum concentration followed by degradation during
the stationary phase.
 This temporal pattern of AI-2 concentration allows the regulation of
gene expression.
Recently a 4th type of quorum sensing system has been identified
in several groups of Gram-positive streptococci.
This new type is called ComRS, which involves sensing a small
double-tryptophan signal peptide pheromone (XIP) inside the cells
after its internalization by an oligopeptide ABC transport system.
Once internalized, the XIP pheromone interacts with a
transcriptional regulator, ComR, proximal regulator of sigX that
encodes a master regulator or alternative sigma factor SigX
(ComX), in turn activating later competence genes for genetic
transformation.
Interestingly, S. mutans has been found to possess both ComCDE
and ComRS quorum sensing systems that regulate bacteriocin
production and genetic competence, respectively.
Anti-Quorum Sensing
Anti-QS agents can abolish the QS
signaling and prevent the biofilm
formation, therefore reducing
bacterial virulence without causing
drug-resistant to the pathogens,
suggesting that anti-QS agents are
potential alternatives for antibiotics.
How Does QS Affect Bacterial
Growth?
●
●
●
Quorum sensing increases the ability of the bacteria to
have access to nutrients or to more favorable
environmental niches and enhances bacterial defenses
against eukaryotic hosts, competing bacteria, and
environmental stresses.
However, on the role of quorum sensing in food spoilage or
in the growth and/or toxin production of pathogens present
in food.
Several compounds have been isolated or synthesized that
antagonize quorum sensors, and application of these
antagonists may potentially be useful in inhibiting the
growth or virulence mechanisms of bacteria in different
environments, including food.
Characteristics of QS
For the bacteria to use quorum sensing constitutively,
they must possess three characteristics:
o To secrete a signaling molecule, an auto-inducer.
o Detect the change in concentration of signaling molecules.
o And to regulate gene transcription as a response.
QS Controls Bacterial
Pathogenicity
Quorum sensing is thought to afford pathogenic bacteria
mechanism to minimize host immune responses by
delaying the production of tissue-damaging virulence
factors until sufficient bacteria have amassed and are
prepared to overwhelm host defense mechanisms and
establish infection. Bacterial pathogens use common
regulatory mechanisms, such as alternative sigma
factors and two component signal transduction systems,
to control the expression of their virulence genes in
response to environmental conditions encountered
during infection of the human host, including changes
in temperature, pH, osmotic strength, oxygen availability,
and nutrient conditions.
Thank You!
Hope you enjoyed 
Introduction
What are bacteria? Bacteria are singlecelled, or simple, organisms that are
invisible to the naked eye. Many bacteria
are found both inside and outside of
organisms, including humans. Bacteria
are also found on surfaces and in
substances like water, soil, and food,
making them key players in the Earth's
ecosystems. They constitute a large
domain of prokaryotic microorganisms.
Contents of this presentation
Bacterial
interaction
-Definition
-Types of interactions
-Bacterial interaction
under stress
-Why do bacteria
communicate with each
other
-steps of bacterial
communication
-Advantages and
disadvantages
-How do bacteria
communicate with each
other using quorum
sensing
Quorum
sensing
-Definition
-how it is done
-quorum sensing in gram
+ and gram – and the
difference between
them
-types of quorum
-antiquorum
-Affection of quorum in
bacterial growth
-bacteria control
pathogenicity with
quorum sensing
Problem vs solution
Problem
Solution
Mercury is the closest
planet to the Sun and the
smallest one in the Solar
System—it’s only a bit
larger than the Moon
Venus has a beautiful and
cute name and is the
second planet from the
Sun. It’s hot and has a
poisonous atmosphere
Carbohydrates
●
Saturn is a gas giant and has several rings. It's composed mostly of hydrogen
and helium. It was named after the Roman god of wealth and agriculture
●
Neptune is the farthest planet from the Sun. It's also the fourth-largest object
by diameter in the Solar System
●
Earth is the third planet from the Sun and the only one that harbors life in the
Solar System. This is where we all live on
●
Despite being red, Mars is actually a cold place. It's full of iron oxide dust,
which gives the planet its reddish cast
Did you know this?
In the human body there are 10 times more bacteria than cells,
they fulfill very important functions
Approximately 8% of DNA is derived from viruses that at some
point entered the body of our ancestors
Despite knowing about 10,000 species, it is estimated that this is
less than 1% of the species that inhabit the Earth
Feature of
the topic
You can enter a subtitle here if you need it
03
Characteristics of life
1
Growth and development
It’s the closest planet to the Sun
2
Energy metabolism
Venus is the second planet from the Sun
3
Homeostasis
Mars is actually a very cold place
4
Adaptation
Jupiter is the biggest planet of them all
5
Response to stimuli
It’s composed of hydrogen and helium
6
Organization
It’s the farthest planet from the Sun
7
Reproduction
Pluto is now considered a dwarf planet
Data
90%
42%
64%
It’s the closest planet
to the Sun
Venus is the second
planet from the Sun
It’s the farthest
planet from the Sun
Type of organisms
Organisms
Unicellular
organisms
Amoeba
Bacteria
Multicellular
organisms
Paramoecium
Plants
Animals
Awesome
words
3/4
body bacteria live in our intestines
500
species have been found in oral flora
1M
of germs hide in a bath sponge
Map
Neptune
It’s the farthest
planet from the Sun
Mars
Despite being red,
Mars is a cold place
Saturn
Saturn is a gas giant
and has rings
04
About
the topic
You can enter a subtitle here if you need it
Elements of living organisms
Carbon
Hydrogen
Nitrogen
It’s the closest planet
to the Sun
Venus is the second
planet from the Sun
Mars is actually a very
cold place
Oxygen
Phosphorus
Sulfur
Jupiter is the biggest
planet of them all
It’s composed of
hydrogen and helium
It’s the farthest planet
from the Sun
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100,000,000
is the number of bacteria that we
eliminate through the feces each day
Definition of concepts
Organism
Nutrient
It’s the closest planet to
the Sun and the smallest
in the Solar System
Venus has a beautiful
name and is the second
planet from the Sun
Protein
Bacteria
Despite being red, Mars is
actually a cold place. It’s
full of iron oxide dust
Jupiter was named after
the Roman god of the
skies and lightning
This is a graph
Venus
Venus is the second
planet from the Sun
Jupiter
Jupiter is the biggest
planet of them all
Follow the link in the graph to modify its data and then
paste the new one here. For more info, click here
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