Autoinducers & Biofilm Formation Flashcards
What is the relationship between the level of autoinducers and the number of bacteria in the environment?
The level of autoinducers is directly proportional to the number of bacteria in the environment
( the number of bacteria in the environment increase, the level of autoinducers increase)
What happens when there is a low cell density?
There is a basal production of autoinducers
No biofilm formation
What happens when there is a high cell density?
There is a high concentration of autoinducers
Triggering a group response, involving gene activation/deactivation
Biofilm formation starts
What is such communication between bacteria termed as? Describe its mechanism
Quorum sensing is the regulation of gene expression in response to the fluctuations in cell-population density
Quorum sensing bacteria produces and releases autoinducers that increase in concentration as a function of cell density
The detection of a minimal threshold stimulatory concentration of autoinducers lead to alteration in gene expression
Bacteria from different species can communicate with each other
Describe quorum sensing in Gram-negative bacteria
Gram-negative bacteria uses Acyl homoserine lactone to communicate between gram-negative bacteria
AHL reaches threshold concentration, it will bind to and activate the regulatory protein in the cytoplasm
Activated regulatory protein will activate/deactivate gene expression
Activation of gene expression will result in the production of quorum-dependent proteins and more enzyme to produce AHL
What are the steps for biofilm formation?
- Free-living cells will attach to surfaces via weak reversible adhesion
- Primary colonizers anchor themselves irreversibly and more permanently on the surfaces by producing sticky extracellular polymeric substances
- Primary colonizers facilitate arrival of other cells by providing more diverse adhesion sites and building up of the polysaccharide matrix that hold the biofilm together.
Nutrients accumulate and the attached cells start to divide
- Fully mature biofilm change in shape and size
Polysaccharide matrix serves as a protective coating and barrier to harmful compounds for the cell, enhancing its survival
- Single-dividing cells will be periodically dispersed from the biofilm to spread and colonize new surfaces
Describe quorum sensing in Gram-positive bacteria
Gram-positive bacteria use autoinducing peptides to communicate between gram-positive bacteria.
When AIP reaches threshold concentration, it will bind to and activate sensor proteins. Activated sensor proteins will then activate regulatory proteins which will then activate/deactivate gene expression.
Activated gene expression will result in the production of quorum-dependent proteins and AIP
EXTRA: Suggest a reason why does the autoinducer of one Gram-negative bacterial species rarely influence the expression of target genes in another Gram-negative bacterial species?
Structures of autoinducers for the different species of bacteria are different from each other
Bacteria will produce a unique AHL, other species of gram-negative bacteria would not be able to respond to it as they have trouble recognizing and binding to the regulatory protein
Therefore, the gene will not be activated/deactivated
EXTRA: Combating infections (with the use of drugs)
Drugs will block the release of autoinducers/stop their receptors
Blocking the ability of bacteria to communicate with each other
Bacteria cannot communicate with each other
Bacteria cells will never know if their numbers are enough to release toxins
Hence, preventing infections
