1. MICROBIOLOGIA GENERALE
Interactions among bacteria: cooperation and competition

2. An example of a microbial consortium
Green: Pseudomonas putida
Red: Acinetobacter sp. ADP1
Citrate Chlorobenzoate

3. The social life of bacterial community : from the individual behaviors to group behaviors

4. Quorum Sensing

5. Quorum Sensing
Quorum Sensing. Bacteria synthesize and secrete autoinducers, low MW molecules that diffuse away into the surroundings. Bacteria in the environment sense the local density of these autoinducers via quorum sensing receptors. Above a certain concentration threshold (the quorum), binding of the autoinducer ligand is synchronized among bacteria. The binding event is transduced into transcriptional and translational changes that result in coordinated shifts in group behavior, e.g. virulence, bioluminescence, virulence biofilm formation, competence.

6. Schematics of quorum sensing systems in Bacteria
Gram negative Gram positive

7. Quorum Sensing in Gram negactive Bacteria

8. Quorum Sensing in Gram-negative bacteria

9. Quorum Sensing Autoinducers
AHL: Acyl Homoserine Lactone

10. Vibrio fischeri: a bioluminescence bacteria and quorum sensing
Luciferase
FMNH2+O2+RCHO FMN+RCOOH+H2O+Light

11. The LuxR response regulator

12. Quorum Sensing in Gram-positive Bacteria: Streptomyces
GBL: y-ButyroLactone
The Sreptomyces griseus A-factor regulon. The diffusible A-factor (a γ-butyrolactone) binds the intracellular receptor ArpA and activates expression of the transcriptional activator AdpA which in-turn regulates multiple phenotypes either indirectly via a multi-step cascade, such as the development of aerial hyphae and sporulation, or directly, such as the production of secondary metabolites like streptomycin.

13. Quorum Sensing in Gram-positive Bacteria: Staphylococcus aures
AgrD pheromone

14. Quorum Sensing in Gram-positive Bacteria: Staphylococcus aures
The AgrD-dependent transcriptional regulation of the agr operon

15. Quorum sensing and antimicrobial agents: the nisin of Lactococcus lactis
Nisin is a 34 aa polycyclic antibacterial peptide
produced by L. lactis that is used as a food preservative

16. Quorum Sensing and Bacterial Virulence

17. AHL: AI-3 that induces virulence genes
Quorum sensing regulation of bacterial virulence factors
E. coli O157:H7
AHL: AI-3 that induces virulence genes
(motility and secretion of the enterotoxin)
S. aureus
AIP: autoinducing peptide induces via a TCRS a range of virulence proteins (damage of host cells and interference with immune system)

18. The QS LasR/LasI and RhlR/RhlI systems of Pseudomonas aeruginosa

19. Microbial Biofilms

20. Bacterial Biofilms in Humans

21. Biofilm Formation
Biofilm formation is often described as a multistep process in which bacteria adhere to an abiotic or biotic surface, through surface charges and production of pili, fimbriae, and exopolysaccharides. After initial attachment, three-dimensional development starts with the building of microcolonies, in which different species already interact. The next step, biofilm maturation, is dependent on matrix production, which ensures cohesion and the three-dimensional structure of mature biofilms. The final step in biofilm formation is cellular detachment, by which bacteria regain the planktonic lifestyle to colonize other surfaces.

22. Biofilm Formation

23. Biofilm formation and quorum sensing

24. Biofilms and Quorum Sensing

25. Macromolecules and bacterial cell structures
involved in biofilm formation
LPS
Flagella
Pili
Fimbriae
EPS (ExoPolySaccharide)

26. bacterial aggregates without a solid support
Bacterial floccules:
bacterial aggregates without a solid support