Karteikarten
Lecture 26 PMB
Karten in diesem Stapel (22)
- 1microenvironmentsthe habitat that bacteria experience, considering their microscopic size
- 2What is the main limit in access to nutrients?Diffusion of bacterium --> microbes often only get intermittent exposure to nutrients
- 3Why do cells grow faster in laboratory cultures than in nature?In nature...
1) Resources/growth conditions suboptimal
2) Distribution of nutrients is not uniform
3) Microbes must grow in mixed communities with other competitors - 4benefits of living on a surfacesurfaces offer access to nutrients, protection from predation, and a means of not being washed away from an environment
- 5microcoloniesclusters of a few cells that develop from a single attached cell
- 6microbial matsbiofilms can thicken into this if no natural predators, has different types of strata in different layers
- 7Biofilms--> group of bacteria enclosed in adhesive, self-produced matrix
--> made with exopolysaccarides, proteins, and nucleic acids
--> may adhere to a surface or float in mats
--> typically multi-species communities
--> diff growth rates, tx profiles, better antibiotic resistance - 8Biofilms relevance in human health/industry-biofilms can grow on medical machinery!
-have enhanced antibiotic resistance
-can contaminate drinking water/fuels
-may also corrode essential pipes and cause water born disease outbreaks
-form dental plaques --> promote tooth decay - 9Biofilm EPS secretionEPS = extracellular polysaccharides
--> VERY hydrophilic, protect from desiccation
--> help with sorption, enzyme retention, cooperation, competition, tolerance/resistance, and localized gradients *REVIEW* - 10How are chemical gradients stabilized within biofilms?different strata of organisms have different metabolisms --> an O2 gradient is formed, with Aerobes > Fermenters > Anaerobes
Active cells form a different strata than dead, starving or dormant cells --> nutrient gradient forms
not to mention: quorum sensing gradient and pH gradient also form - 11How do biofilms tolerate a higher level of antibiotics than identical planktonic cells?antibiotics/toxins that diffuse into the matrix react with many components --> lower concentrations of toxin in biofilm
ALSO
some drugs are inactivated by binding to biofilm matrix, drugs have greater effects on fast growing cells, and biofilm bacteria have different patterns of gene expression - 12Crystal violet assay for biofilm formation: methodssuspend bacteria in liquid, pipette into wells of plate --> grow cells without vegetation --> remove cell suspension, wash --> add crystal violet solution --> remove crystal violet, wash --> amount of remaining crystal violet indicates adherent cells + extracellular biofilm matrix!!!
- 13Biofilm formation: stepsPlanktonic bacteria use flagella to reach surface --> surfaces sensed by outer membrane proteins, hindrance of flagellar rotation, or increased tension on pili --> change in gene expression to produce EPS, stop motility, express adhesion proteins, secrete extracellular enzymes --> maturation of biofilm until dissolution
- 14How do extracellular signals cause internal changes that lead to biofilm formation?motile --> sessile comes from increase in conc. of cyclic di-GMP
- 15c-di-GMPsecondary messenger, synthesized by DGC and hydrolyzed by PDE
levels of c-di-GMP are sensed by receptor proteins that bind this molecule
--> binding causes receptor activities to change --> downstream effects - 16DGC and PDEboth activities are regulated by attached signaling domain (ie: two component receiver domain)
specificity of these two is a mystery, conc. in cell doesn't seem to matter
--> spatially segregated c-di-GMP is the only active version? - 17Wsp system of P. aeruginosasimilar to chemotaxis
surface binding somehow transmitted to MCP WspA --> increased WspE autophosphorylation + increased phosphotransfer to WspR --> activates DGC --> ci-d-GMP produced using two GTP - 18specific genes turned on by c-di-GMPpel and psl genes: activated by increase in ci-d-GMP, encode for EPS production
also genes that encode for pilus-like adhesion proteins - 19analog of Wsp system to chemotaxisMCP = WspA
linker = WspB
Histidine kinase = WspE
Response regulator = WspR (for DGC) - 20Tension dependent surface sensing (in P. aeruginosa) chemotaxis system **Type IV pili**When T IV pili senses rapid tension upon contact with surface: PilJ, PilI, and ChpA complex activate:
--> PilT and PilB, which then assemble PilA subunits to retract and pull cell to surface (positive feedback of twitching & sensing)
--> CyaB, which increases cAMP and in turn increases Vfr AS WELL AS c-di-GMP - 21tension retraction system analogsPilJ = MCP
PilI = CheW linker
ChpA = CheA
PilG and PilH = CheY (activate CyaB, PilT, and PilB)
Vfr: cAMP binding tx activator of virulence genes!! (Not in chemotaxis) - 22How do cells escape biofilms?release enzymes that degrade biofilm polymers
or
a drop in c-di-GMP?