Lecture 14 - bacterial community Flashcards
What type of competition is implemented with Type V and VI secretion systems
Contact dependent
What type of competition is implemented with bacteriocins
Contact independent
How was the type V secretion system discovered
K12 E.coli could not survive in culture with non-K12 wild isolate
How large is the type V secretion system pilus?
About 33 nm
What genes encode the type V secretion system?
cdiB, cdiA, and cdiI
CdiB
beta barrel protein that is required for export of the type V secretion pilus
CdiA
33 nm pilus for type V secretion system
CdiI
Confers immunity to the toxin exported by the type V secretion system
Steps of type V secretion
- Receptor binding domain on the end of the pilus binds its receptor
- Toxin is exported to the target cell
- Toxin is taken up by target cell through an outer membrane protein and inner membrane transporter
How many kind of toxin are exported in type V secretion?
One
What kinds of toxins are secreted in type V secretion?
DNase, tRNAse, pole formers
What are pole-forming toxins?
Disrupt the charge differential across cell membranes
How does the type V secretion system get toxin into the target cell?
Hijacking of regular transport proteins already expressed on the cell surface
How does the type VI secretion system get toxin into the target cell?
Needle-like tip of the pilus punctures the cell exterior
How many types of toxins are secreted in type VI secretion?
Many different kinds to cover all possibilities in the target cell
What is an example of a bacteriocin?
Colicin
When is expression of colicin triggered
During the SOS response
What genes encode the colicin system?
colA, immA, lysA
Steps of colicin system implementation
- immA is expressed at all times (different promoter from colA) and provides immunity to toxin in Col+ cells
- extensive DNA damage induces SOS system and expression of colA
- LysA punches holes in damaged cell to release toxin and immunity protein into surroundings
- toxin is delivered to surrounding cells
Do all cells get affected by ColA when it is released?
Col+ cells are always encoding the protein for immunity, so they are not affected. Only Col- cells are affected
What kind of toxin is delivered by colicin system?
Nuclease
Components of colicin protien
- translocator domain
- receptor binding domain
- effector domain
How does colicin get into target cells?
Recognizes BtuB on outer membrane and imports toxin to target cell through OmpF
What kinds of bacteria are type V and VI secretion and bacteriocins useful against?
Gram negative
Quorum sensing
Process where bacterial cells coordinate gene expression depending on population density
How was quorum sensing first discovered?
Discovered in Vibrio fischerii, a bioluminescent bacterium that colonizes the light organ of the Hawaiian bobtail squid
Use of bioluminescent bacteria for squid
Counterillumination hides the squid’s shadow from predators
How is the quorum-sensing gene system induced?
- Accumulation of a secreted autoinducer in cell surroundings
- Autoinducer enters neighboring cells
- Autoinducer binds receptor proteins that act as transcription factors
What is the quorum-sensing gene system in Vibrio fischerii
LuxR-autoinducer complex activates transcription of protiens incuding LuxA and LuxB
What causes bioluminescence in Vibrio fischerii?
Luciferase made by LuxA and B
Possible functions of quorum sensing systems
- bioluminescence
- exoenzyme production
- extracellular toxin production
- antibiotic production
- cell division
- conjugation
