QUORUM SENSING IN BACTERIA

Submitted to - Submitted by - Prof. H. K. Kehri Sameen ZaidiProf. A. Dikshit Vandana Kumari M.Sc. III sem 2014 - 2015

WHAT IS QUORUM SENSING ?

• ‘Quorum’ is a Latin word.

• It means the number of members of a group required to be present to transact business or carry out an activity legally

• In this process bacteria communicate via secreted signalling molecules called “autoinducers”, which contribute to the regulation of the expression of particular genes.

OCCURRENCE –

• Within a single bacterial species as well as between diverse species.

• In some local insects use quorum sensing to determine where to nest.

HISTORY OF QUORUM SENSING

• The first such system was described in Vibrio fischeri (Nealson &Hastings, 1979), a symbiotic species that provides its marine eukaryotic hosts i.e., Squid with light.

Euprymna scolopes

GENERAL MECHANISM

• Bacteria showing quorum sensing requires two things –

(1) Signalling molecules called autoinducers or pheromones.

(2) A receptor that can specifically detect the signalling molecule.

• When the inducer binds the receptor , it activates transcription of certain genes, including those for inducer synthesis.

QUORUM SENSING IN GRAM NEGATIVE & GRAM POSITIVE

BACTERIA

• Quorum sensing in Gram-negative bacteria - The language of LuxI and LuxR genes.

• Quorum sensing in Gram- positive bacteria – Peptide mediated quorum sensing.

In Gram negative bacteria

• Autoinducer – AHL or N-acyl homoserne lactones.

• It is synthesized by a LuxI homologue and a LuxR homologue.

Example 1 - Quorum Sensing in Vibrio fischeri – Bioluminescence.

• Bioluminescence is defined as the emission of visible light from living organisms.

• Bacteria are the most numerous of the light emitting life forms.

• One of the most widely studied bacteria is Vibrio fischeri.

Quorum sensing in Vibrio fischeri at low and high cell density

Example 2 – Antibiotic Production in Erwinia carotovora

• Barrie Bycroft, Paul Williams & George Salmond were studying mutants of Erwenia caratovora that were unable make carbapenem (CarR) antibiotics

• One class of mutants could not make antibiotics on their own but could do so when cross fed by a second group of mutants.

IN GRAM POSITIVE BACTERIA

• Eg.- Bacillus subtulis & Streptococcus pneumonia use quorum sensing to develop bacterial competence.

• Autoinducer – peptide (oligopeptides).

• Secreted by – ABC transporter (ATP binding cassette transporter

MECHANISM• Peptide signal works by binding to a sensor protein “

histidine kinase “, located in the cell membrane of the bacterium.

• Histidine kinase become activated .

• Activation of the histidine kinase leads to phosphorylation of response- regulatory gene, and interaction with another regulatory protein facilitates transcriptional activation (for RNA III).

GENERAL MECHANISM OF QUORUM SENSING IN GRAM POSITIVE BACTERIA

• RNA III affects the transcription or translation of the target gene.

• Peptide used as autoinducer in Gram Positive Quorum Sensing is secreted through ATP Binding Cassette transporter(ABC).

• ABC transporter are transmembrane proteins that utilises the energy of ATP binding & hydrolysis to carry out certain biological processes.

Example- ComD/ComE competence system in Streptococcus pneumoniae

• 5 genes have been implicated in the regulatory circuit for competence development.

• Auto inducing peptide signal to develop the competence state is called CSP (Competence Stimulating Peptide). .

• ATP Binding Cassette transporter of ComAB processes and secretes the competence stimulating peptide in the extracellular region.

ComD/ComE competence exhibited by Streptococcus pneumoniae

• ComD is a sensor kinase protein which detects the accumulated CSP at higher cell density.

• Higher than the threshold levels of CSP induce auto phosphorylation of ComD transferring the phosphoryl group to the response regulator ComE.

• Phosphorylated ComE activates transcription of comX gene.

WHY DO BACTERIA TALK TO EACH OTHER? OR WHAT IS THE NEED OF

QUORUM SENSING ? As environmental conditions often change rapidly,

bacteria need to respond quickly in order to survive.

1) Quorum sensing enables bacteria to coordinate their behaviour.

2) It is very important for pathogenic bacteria during infection of a host to coordinate their virulence in order to be able to establish a successful infection.

EVOLUTION OF QUORUM SENSING SYSTEMS IN BACTERIA HAVE BEEN ONE OF THE EARLY STEPS IN THE DEVELOPMENT OF MULTICELLULARITY

• Although bacterial quorum sensing systems differ in every case the ability to communicate with one another allows bacteria to coordinate the gene expression & therefore coordinate the behaviour of the entire community

• Presumably this process bestows upon bacteria of the qualities of higher organisms.

• Evolution of quorum sensing systems in bacteria could therefore have been one of the early steps in the development of multicellularity.

QUORUM SENSING INHIBITOR

• Efforts to disrupt biofilms have enabled the identification of bioactive molecules produced by prokaryotes and eukaryotes.

• These molecules act primarily by quenching the QS system. The phenomenon is also known as QUORUM QUENCHING .

• QS inhibitors are molecules that interrupt the pathway of communication bacteria used to regulate expression of virulence factors.

EXAMPLES• N-Acyl homoserine lactonase, encoded by aaiiA,

attacks the lactone bond, causing ring opening of AHLs.

• Transgenic plants harbouring the aiiA gene from Bacillus thuringenesis were less prone to maceration by Erwinia carotovora.

• Other bacteria including Arthrobacter sp, Klebsiella pneumonia, Psedomonas sp., Variovorax sp.., etc., harbour enzymes capable of AHL destruction.

• Best studied example of QS inhibition stems from a marine alga – Delisea pulchra.

• It produce several halogenated furanone compounds capable of interfering with AHL- mediated signalling in bacteria.

• It prevent the AHL from binding to the luxR homologues & eventually cause a rapid turnover of these proteins.

• Manefield et al demonstrated the potential of the halogenated furanones in preventing the pathogens Vibrio harveyi from infecting the commercially important black tiger Paneus mondon.

QUORUM SENSING IN SOCIAL INSECTS

1. ANTS - Colonies of the Temnothorax albipennis nest in small crevices between rocks. When the rock shift & nest is broken open, these ants must quickly chose a new nest to move into

• HONEY BEES – Apis mellifera also use quorum sensing to make decisions about new sites

COMPUTING & ROBOTICS –

• Quorum sensing can also be used to coordinate the behaviour of autonomous robot swarms.

• Using a process similar to that used by Temnothorax ants , robots can make rapid group decisions without the direction of a controller.

LIST OF VARIOUS RESEARCH INSTITUE WORKING ON QUORUM SENSING

• University of Nottingham.

• Princeton university – Department of molecular biology.

• J. Craig Venter Institute.

• Helmholtz Centre for Infection Research.

• National Institute of General Medical Sciences.

IN INDIA –

• Institute of Technology Bombay, Powai, Mumbai.

• Institute of Technology, Chennai.

• Yenepoya Research Centre, Yenepoya University, Mangalore.

• National Botanical Research Institute, Lucknow.

QUESTIONS

1) Define quorum sensing in bacteria ?

2) Name the bacteria in which quorum sensing was first discovered and who discovered it.

3) Differentiate between Gram negative and Gram positive bacteria with reference to quorum sensing only.

4) What are autoinducers ? Explain with reference to both Gram negative & Gram positive bacteria.

5) How quorum sensing is beneficial to Euprymna scolopes ?

6) Give a detailed mechanism of quorum sensing in Gram positive bacteria with reference to competence in bacteria.

7) What is the full form of ABC ? What is the role of ABC in quorum sensing?

8) Explain quorum quenching with example.

9) Write short note on quorum sensing in social insects.

10) List various research centres working on quorum sensing.

REFERENCES

• Google.

• Life Sciences – Fundamentals & Practice , Part 1

By – Pranav Kumar & Usha Mina.

• Papers – Bacterial bioluminescence: its control and ecological significance by Nealson K.H. , Hastings, J.W.(1979).

• How bacteria talk to each other by quorum sensing by Bonnie L. Bassler.

THANK YOU