BIOL243 - L6

  • Created by: Katherine
  • Created on: 04-04-17 19:21
What is a biofilm?
A conditioning film comprised of organic and inorganic particles.
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How does bacteria arrive at a surface?
Diffusion, motility chemotaxis, turbulence impaction
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What is motility chemotaxis?
They swim to the surface
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What is turbulence impaction?
The flow of air or liquid might push the bacteria to the surface
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What is a boundary layer?
Below the flow there is an area of calm where there is no turbulence. Diffusion can occur here.
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How does bacteria attach to a sruface?
Resersibly bound, via brownian movement (random attachment) or reversibly bound with bridging structures (e.g. cilia, flagella), or irreversibly bound with exopolymer deposition (the bacteria produces polysaccharides), it might switch it's phenotype
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What happens when you have sessile bacteria?
A change in gene expression: microarrays and protemoics show around 50-60 changes, down regualtion of planktonic genes. Flagella: Upregulation of sessile genes. Stress Proteins: Capsule: Alg genes (over production of alginate - an EPS
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What is the role of expolymeric substances?
To act as cellular cement, to form the matrix framework, to provide structure and integrity and to give biofillms a defined architecture.
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What do we call the architecture of biofilms?
Stacks - they are 3D structures. The cells come very close together. Eventually you also get detachment. The stacks are called mushroom stacks. There is alot of bacteria in the matrix. There are numerous channels in there.
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What are the features of biofilm architecture?
Numerous channels, water flow (input of fresh nutrients, oxygen ect, export of waste) channels are essential for the development of the biofilms.
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How are biofilm stacks made?
Cell division and increase in number. Increase in matrix and therefore the production of microbial stacks. Higher growth rates at the biofilm surface.
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What are streamers a result of?
High flow and excessive growth
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Do you get more architecture with high flow or low, high nutrient level or low?
High of both
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What is the composition of biofilm matrix?
Cells, water, biosynthetic microbial polyers absorbed materials
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How are cells embedded in the biofilm matrix protected?
Protected from desiccation, increased flow rates, predation and antimicrobial compounds (embedded cells are more resistant than their planktonic counterparts)
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How are biofilms difficult to kill?
In some cases need x1000fold higher concentration of antimicrobial agent (compared to that required to kill suspended counterparts), cells embedded in a matrix - less diffusion, other features e.g. cell to cell signalling
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What are the processes of cell to cell signalling?
Synthesis, recognition, response
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What is the synthesis phase of cell to cell signalling?
They produce chemical signals
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What are the chemicals produced the cells to signal?
Small diffusible chemical signals. For gram -ve, AHLs (N-acyl homoserine lactone), and for Gram +ve signalling peptides. They are known as autoinducers
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How often are autoinducers released by cells?
Constitutively (constantly) in low numbers
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How do cells connect to autoinducers?
Lock and key mechanism
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For gram -ve bacteria, how many autoinducers are required?
The AHL concentration must exceed a threshold (quorum) to form an AHL/Activator complex.
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What happens where there are enough AHLs?
Initiates a coordianted response in all cells of the population - Quorum Sensing.
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How do you get a co-ordinated response?
Cells sense local population density and have a coordinated local population response. Swutching on genes, or up regulating those that are beneficial when a critical mass has been reached.
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What happens in a coordinated response?
Transcription begins in all cells when a threshold density is reached
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What happens in a non coordinated response?
The bacterial concentration is proportional to the gene product.
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What are the Lux R and I responsible for?
Regulatory genes, encode for AHL and activator protein, promoters for both operons
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What are the other areas of the Lux regulor responsible for?
Structural genes, encode for light production or virulence genes.
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Which is the speaking Lux? I or R?
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Why AHL systems exist in P.aeruginosa?
The Las and Rhl systems
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What does the Las system respond to?
Responds to the autoinducer: OdDHL, which is produced by Lasl synthase (PA1432) and recognised by LasR.
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What does the Las system do?
It controls the production of multiple virulence factors involved in acute infection and host cell damage, including the LasA and LasB elastases, exotoxin A and alkaline protease.
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What does Rhl produce and respond to?
To C4-HL (BHL). This molecules is generated by the Rhll synthase and sensed by the transcriptional regulator, inducing the expression of several genes.
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What does Rhl induce the expression of?
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What type of relationship is between Las and Rhl systems?
A hierarchial relationship: the Las system controls the Rhl system as the 3-oxo-c12-HSL las R complex directly upregulates RHLT transcription. Activatino of the LasIR system allows the activation of the RhlIR system.
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What happens when a threshold concentration of 3-oxo-c12-HSL is produced?
the 3 oxo-c12-HSL -LasR complex binds the promoter regions of multiple genes , activating or repressing their transcription. Among the genes upregulated are LasI, which enhances the production of 3-oco-c12-hsl, and rhlR.
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What does production of RhlR do?
It increases the production of the rhl response regulator RhlR, activating a second AHL pathway at an earlier stage.
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How does programmed detachment occur?
Synchronised liberation of daughter cells, they may be more hydrophilic than other cells. There is a change in the lipopolysaccharide and downregulation of high mwt LPS, leaving low mwt LPS. They are shot out of the biofilm
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What is sloughing?
It is the physical removal of cells from the biofilm
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Why does sloughing occur?
Increased turbulence, scouring caused by a decrease in oxygen or nutrients (the less attached are removed),
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What can happen to the detached cells?
They can go back and form a new biofilm
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Card 5


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