Biofilm Formation- Lecture 5 Flashcards
Bacterial Biofilms
Population of bacteria encased in exopolymeric substances (EPS)
What behvaiours do bacterial biofilms stimulate?
(1) Competition: production of bacteriocins, antibiotics, and inhibition of quorum sensing (leads to programmed cell death
(2) Cooperation: Ammonia nitrifies and nitrite oxidizers
(3) Communication: AHL (acyl hormone serine lactone) and nanowires
Development of biofilms
(1) initial attachment: using pili and adhesions
(2): early development: synthesis and export of exopolysaccharide (most common EPS)
(3) Mature biofilms: lay in a dormant state, resistant to antibiotic treatment that targets live and growing cells
(4) Sporulation, PCD and dispersal of spores to form new biofilms
Wsp System
A chemosensory system that allows for the switch from planktonic to the biofilm lifestyle
1. Wsp-R (Mechanosensor, sensor kinase) detects grows on a surface
2. Phosphorylation of Wsp-D and Wsp-B
3. Phosphorylation and activation of GGGEF enzymes (diguanylate cyclase)
4. GGGEF enzymes catalyze synthesis of ci-di-GMP through 2 GTP
Mechanisms of inhibition of diguanylate cyclase
(1) Phosphorylate-dependent inhibition: dephosphorylation of Wsp-R, causes return to a planktonic lifestyle
(2) Phosphorylation independent mechanism: ci-di-GMP fuses to form ci-di-GMP2, binds to allosteric site on diguanylate cyclase leading to disassembly of the active site (homodimer)
What substances can be found in biofilms?
polysaccharides, DNA and proteins
Benefits of exopolysaccharides in biofilms
Promotes cell-to-cell and cell-to-surface adhesion and has high water rendition, preventing the drying out of the biofilm, provides habitat and offer protection from environmental insults
How does ci-di-GMP activate the synthesis of exopolysaccharide, Cellulose
Ci-di-GMP binds to BcsA (Cellulose synthase) activating cellulose synthesis (B-1,4 linked glucose) at the inner membrane
synthesis of cellulose used nucleotide-activated precursors: UDP-glucose
BscB allows for export of cellulose outside of the cell
Benefits of proteins in biofilms
Promotes cell-to-surface adhesions, also called adhesions
What protein synthesis system is used by P. aeruginosa to transport proteins across the cell envelope
Uses T5SS (CdrA passenger and CdrB beta barrel)
How does T5SS (Cdr) system synthesize and export protein to the outer membrane
- Proteins contain a Sec signal for export (signal peptide)
- Proteins are exported into periplasm unfolded, using SecYEG + SecDF channel using energy from the SecA ATPase
- proteins sec signal is cleaved by SPase during membrane translocation
- For Gram-negative bacteria, the protein is exported using porins at the OM
T5SS
The protein secretion system in Gram-negative bacteria includes auto transporters and two-partner transport systems
- T5SSb is used by P. aeruginosa to export CdrA to the cell surface (adhesion, protein)
How is CdrA exported to the cell surface?
- contains two separate signal peptidases so transport is separate
