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Cell-cell communication process that bacteria use to coordinate group behavior or responses

Survival strategies that bacteria use and include bioluminescence virulence factor production, sporulation, biofilm formation and motility

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Since no gene expression

bacteria like Vibrio fischeri remain “dark”

Save energy and ensure bioluminescence is not wasted

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mechanism overview: low cell density (yiling)

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mechanism overview: low cell density (yiling)

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Lux R and lux I genes = slightly active à producing small amounts of Lux R and Lux I proteins

Lux I make small amount of AHL molecules but stay at a very low level in the environment

Amount of AHL outside cell = fall below threshold concentration

--> cannot bind to Lux R = inactive = cannot bind to lux promoter = lux operon is not switch on

--> no gene expression of lux operon = behaviors like bioluminescence do not happen

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How does it help squid to survive? (yiling)

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How does it help squid to survive? (yiling)

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Effective camouflage for the squid

At low bacterial density, the bacteria inside the squid don’t glow, keeping the squid safe from predators. As the bacteria grow, they start to glow, helping the squid blend in and hide

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Autoinducers in Gram-negative bacteria (zhixuan)

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Autoinducers in Gram-negative bacteria (zhixuan)

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1. Acyl Homoserine Lactone (AHL)

Produced and only used by Gram-negative bacteria for intraspecies communication

AHL is a small molecule that is freely diffusible across the cell membrane.

The acyl side chain of AHLs can vary in both length and substitution (short-chain AHL diffuse more freely through membranes, long-chain AHL may require active transport mechanisms)

2. Autoinducer-2 (AI-2)

Produced and used by both Gram-negative and Gram-positive bacteria for interspecies communication.

DPD is synthesized by the enzyme lux S

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1. Lux I (signal synthase)

an enzyme that synthesises AHLs

AHLs diffuses freely across the cell membrane and accumulates in the extracellular environment

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1. Lux R (signal receptor and transcriptional activator)

a receptor protein that detects and binds AHL molecules

once the intracellular concentration of AHL reaches a threshold (high cell density), AHL binds to Lux R.

AHL-Lux R complex then activates/represses the transcription of target genes.

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mechanism overview: high cell density (alesha)

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mechanism overview: high cell density (alesha)

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there will be an increase in population growth through the production of AHL molecules --> caused by more active Lasl enzymes

the AHL molecules accumulates and diffuses back into bacterial cells --> reaches a certain threshold level

AHL will bind to the LasR (protein that binds to quorum-sensing signaling molecules) --> turns into a functional transcriptional regulator

the active LasR binds to target DNA promoters and switches on QS regulated genes

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biofilm formation due to high cell density (alesha) 

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biofilm formation due to high cell density (alesha) 

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during QS activation --> AHL conc surpasses treshold levels and the AHL molecules re enter bacterial cells and bind to LasR, which reactivates it

the activation regulates adhesion proteins, EPS production and biofilm structural genes that ensures the formation of the biofilm structure

the genes then allows bac to transition from planktonic state to a biofilm that is highly organised and protective community

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biofilms protect bacteria from environmental stresses like immune responses in our body

within the biofilm, bacteria share their resources like nutrients and metabolites to improve their efficiency in nutrient poor environments to continue to thrive in untreated person

if the biofilm is found in a patient, its important that they act quick though antibiotics for mild cases to surgically removing the infected area for more severe case

without intervention, the immune system becomes compromised and can lead to common chronic infection caused by the biofilm like pictured above, cystic fibrosis lung infection

because biofilm is so antibiotic resistant because of their EPS --> causes patients to have an increased antibiotic resistance as well that makes treatment more invasive

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Functions regulated by quorum sensing (QS) - ZhiJie

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Functions regulated by quorum sensing (QS) - ZhiJie

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Bacteria coexist with other microbes in competitive environment, and quorum sensing is one of their survival's strategies.

Quorum sensing is one of the processes used by bacteria to coordinate their behavior based on the population density.

Some functions regulated by quorum sensing include:

1) Biofilm formation

Quorum sensing helps bacteria to form biofilms, which are protective layers that help them survive in harsh conditions.

2) Virulence factor production

Some pathogenic bacteria use quorum sensing to regulate the production of toxins and other factors that enhance their ability to cause disease.

3) Sporulation

In some bacterial species, quorum sensing controls the formation of endospores, which are high resistant forms of bacteria.

4) Antibiotic resistance

Bacteria can use quorum sensing to develop and share resistance to antibiotics, making infections more difficult to treat.

5) Bioluminescence

Certain marine bacteria use quorum sensing to produce light, which can be used for attracting prey for symbiotic relationships with marine organisms.

6) Conjugation

The process of genetic exchange between bacteria. Quorum sensing can regulate the expression of genes involved in conjugation, allowing bacteria to share genetic material such as plasmids.

7) Motility

Quorum sensing can control the movement of bacteria, enabling them to move collectively towards a favorable environment or away from harmful conditions.

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1) Reversible/initial attachment to the surface.

Bacteria first attach themselves to a surface using their appendages like pili or fimbriae.

2) Irreversible attachment to the surface due to EPS production.

Once a critical number of bacteria have attached, they start producing extracellular polymeric substances (EPS), a sticky substance that firmly anchors them to the surface and to each other.

3) Microcolony formation and multi-layer of cells adhering to one another.

The bacteria continue to multiply and produce more EPS, forming structured communities. During this stage, the cells communicate through quorum sensing by releasing signaling molecules called autoinducers. When the concentration of these molecules reaches a certain threshold, it triggers the expression of specific genes involved in biofilm formation.

4) Mature biofilm with characteristic ‘mushroom’ architecture supported by EPS.

The biofilm develops a complex, three-dimensional structure with water channels that allow nutrients and waste to be transported. The bacteria within the biofilm can differentiate into distinct subpopulations, each with specialized functions.

5) Detachment and reversal to planktonic growth.

Eventually, some bacteria within the biofilm will receive signals (often through quorum sensing) to become motile again and disperse from the biofilm. This allows them to colonize new surfaces and form new biofilms.

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Benefits of the biofilm to microbes. (ZhiJie)

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Benefits of the biofilm to microbes. (ZhiJie)

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1) Extracellular polymeric substances (EPS) allow the microbes to adhere more stably to the surface, provide mechanical support for the formation of characteristic architectures in the mature biofilm, with fluid channels for the movement of nutrients and waste, as well as provide protection from external environment such as desiccation or presence of antibiotics.

2) Close proximity of bacteria in the biofilm allows efficient synergistic microbial growth

For example, different species may cooperate to break down a common substrate into usable nutrients Also. different species may exchange metabolites and catalyze them further in another pathway. Thus, giving biofilm systems higher metabolic efficiency by maximally utilizing. waste products and makes nutrient sources available for the microorganisms to support their growths.

3) Close proximity of bacteria in the biofilm allows efficient intra- and interspecies cell-cell communication. For example, Al-2 may trigger the production of bacterial surface adhesins and induces coaggregation. between different bacterial species. Also, quorum sensing may increase EPS production in the attached cells. Thus, enhancing biofilm formation.

4) Close proximity of bacteria in the biofilm also creates a favorable condition for genetic material exchange that may enhance survivability by producing populations with antibiotic resistance or higher pathogenicity- (that is ability to cause disease).