Lec 5 - Quorum sensing Flashcards
What are Autoinducers? (AI)
Small quorum sensing molecules
Give an outline to quorum sensing
1) Low population = low conc. AI
2) Increased population = reach AI threshold and activate transcriptional regulator
3) Various expression of genes including virulent factors and sporulation
4) Not a stress response but a “overpopulated” response
What is the autoinducer for gram -ve bacterias
e.g V. fischeri and P.aeruginosa?
homoserine lactone (HSL) and LuxIR
(QseC/AI-3) - Ecoli,salmonella
What is the autoinducers for gram +ve and -ve bacteria?
E.g E.coli, Klebsiella, S. aureus, streptococcus pyogenes
LuxS
AI-2
What are the autoinducers for gram +ve bacteria?
e.g. Stahpylococci, Enterococci, bacilli, lactobaccilli,streptococci
Autoinducing polypeptides (AIP)
binds to a membrane located protein
What is the function of LuxI and LuxR?
LuxI - HSL synthase
LuxR - sensor binding to HSL
LuxR-AHL complex activate virulent factors
HSL’s are membrane permeable and bind to cytoplasmic receptor
What is the difference between LasR and RhIR genes?
LasR activates the virulent genes
RhIR is the virulent gene
Give an outline to the Staphylococci QS system
Composed of RNAII and RNAIII
P2 and P3 drive transcription
RNAII consist of argBDCA operon
argB and D produce AIP
argC for sensing
argA signal molecule
arg is used for invasiveness of bacteria to immune system
arg+ infiltrate tissue
arg- colonise surfaces better and form thicker biofilms.
Control interactions with innate immune system
What is a distinct feature of the structure of AIPs
sulfide bond
Outline arg1/2/3 group specificity?
arg1 - 79%
arg2 - 15%
arg3 - 8%
Give details about LuxS/AI-2 systems
Found in gram + and - bacteria
Diffusible, interconvertible, penetrates
AI-2 is an extracellular signal synthesised by luxS (metalloenzyme)
Production of AI-2 produces Methyl-R
AI-2 is derived from DPD
