Quorum Sensing Flashcards
Bacteria communicate by…to…and reveal..
They release the chemicals and when…builds up to…a…which
Chemicals
Distinguish species
Friend from enemy
The level
Critical, specific
Signal transmitted to the cell
Alerts that they reached a quorum
After reaching a quorum the population acts as….carrying tasks..
Controls behaviours from..and…and..and..
Large coordinated group
Thats would be unsuccessful alone
Symbiosis
Virulence
Biofilm
Natural product production
Why disrupt quorum sensing
Why promote it
Stop harmful bacteria
Valuable products
Quorum sensing relies on…,…,..of extracellular molecules called
Sensed by …
Activates gene expression when
Enables bacteria to alter behaviour in response to…changes in neighbour community
Detection, production, group wide response
Autoinducers
Receptor protein
Reaching a quorum
Population density, species composition
Symbiosis in marine life
V.fischeri bacteria and hawaiian bobtail squid, allows bacteria to grow to a quorum when wanting to hide from predators so they emit light that counter illuminates moonlight
The more the cells the more the..
At a particular…indicative of their number bacteria change..
Inducers
Concentration
Their gene expression
Quorum sensing steps
Production of autoinducers
Release of autoinducers actively or passively
Recognition of autoinducers by receptor proteins when they reach a threshold conc
Change in gene expression
Classes of autoinducers
Intra species, one species
Intra genera, one genus
Inter species, gram negative or gram positive
Quorum sensing indicates ..and..
Number
Species relatedness
Quorum sensing systems
Gram negative»_space; luxl/ luxR
Gram positive» peptide signals, two component signal transduction
Vibrio harveyi» AHL, two component signalling (multiple autoinducers)
v.fischeri is..
gram negative
V. fischeri quorum sensing
LuxI and LuxR
LuxI is the protein responsible for autoinducer production
LuxR is the protein necessary for detecting and responding
autoinducer (AHL)
AHL stands for
acylated homoserine lactone
why no cross talking in gram negative
each species has its own AHL differing slightly in the left carbon chain so only it can respond to it.
steps for gram negative
lux L synthesis, autoinducers accumulate till quorum is reached , sensed by lux R
lux R- AHL complex is an activator binding to a promotor to turn on xyz genes
Gram positive quorum sensing
peptide autoinducer and 2 component adaptive response circuit
the 2 component circuit is composed of
membrane bound protein kinase, initiates information transfer by autophosphorylation
response regulator protein, controls transcription of target genes
autoinducers in gram positive can be
naked peptides or peptides with moieties
steps for gram positive
1.The peptide signal precursor locus is translated into a precursor protein, which is
subsequently cleaved to produce the peptide signal
2.peptide signal accumulates extracellularly till quorum
3.Detection occurs via a two-component
signal transduction circuit
4.phosphorylation “Activation” of a
response regulator protein,
bind promoter DNA and regulate
transcription of target genes (xyz).
v.harveyi is
gram negative bacteria but with multiple autoinducers
has AHL and 2 component circuit and non AHL autoinducer
Is gram + quorum sensing species specific?
yes
v.harveyi systems
System 1: AHL autoinducer-1
AI-1 and Sensor 1 (LuxN)
System 2: non AHL autoinducer
AI-2 and Sensor 2 (LuxPQ)
both to protein called ‘‘LuxU’’ then LUX O then LUX R
genes regulated by v.harveyi
CDABE operon
examples for bacteria and their response after quorum sensing
Vibrio fischeri: Bioluminescence
Pseudomonas aeruginosa: Virulence Factors, Biofilm
Agrobacterium tumefaciens: Mating, Transfer of Mobile DNA
Erwinia carotovora: Virulence Factors, Antibiotic Synthesis
Quorum Quenching
It is the inhibition of quorum sensing using chemical or enzymatic means to
counteract behaviors regulated by quorum sensing.
It interferes with the signaling mechanisms and
shuts down genes
Strategies for Quorum Quenching
1.Inhibition of signal molecule synthesis
2.Degradation of signal molecules
3.Competitive inhibition in the combination of signal
molecules and receptors
degradation of signal molecules
high temp/high pH/ lactonases enzymes all cause lactonolysis
signal molecule synthesis inhibition
(AHLs) substrates
are S-adenosyl methionine (SAM) and AcylAcyl carrier proteins (acyl-ACP)
their analogues can be used
example for signal degredation
plants infected by
E. carotovora increase the pH at the site of infection
AiiA enzyme produced by Bacillus species.
Competitive inhibition
analogues of inducer molecules and thus directly
bind the signal receptor.
4-nitro-pyridine-N-oxide (4-NPO) from garlic extract.
The applications
food and environment
Food>Increasing the shelf
life >counteract food spoilage >Quorum quenching against pathogens
Environment>Bioremediationbiodegradation, biosorption>Quorum sensing>degrade wastes,
remediate the polluted
environment
applications agriculture and medicine
Agriculture>Enhancement in yield and quality of agricultural products>, plant disease control> Quorum quenching> lactonases enzymes
Medicine>Attenuate virulence and prevent microbial infections > Lactonases as anti-virulence, antibiofilm agents>AiiA,
AiiM> quorum quenching>
