MICROBIOLOGIA GENERALE Interactions among bacteria: cooperation and competition

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

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

Quorum Sensing

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.

Schematics of quorum sensing systems in Bacteria Gram negative Gram positive

Quorum Sensing in Gram negactive Bacteria

Quorum Sensing in Gram-negative bacteria

Quorum Sensing Autoinducers AHL: Acyl Homoserine Lactone

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

The LuxR response regulator

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.

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

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

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

Quorum Sensing and Bacterial Virulence

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)

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

Microbial Biofilms

Bacterial Biofilms in Humans

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.

Biofilm Formation

Biofilm formation and quorum sensing

Biofilms and Quorum Sensing

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

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