Surface Structure Flashcards
Other names for EPS
capsular polysaccharides (CPS), capsule, exopolysaccharides, or glycocalyx
If the EPS is covalently linked to the cell surface it is considered?
To be a capsule
If the EPS is loosely associated with the cell surface or free it is considered to be ?
A slime layer
Why is the EPS only found in fresh samples of bacteria or bacteria in nature?
Because cells grown in the lab experience attenuation
-they no longer need their slime layer growing on the media
What is a method to test for the presence of EPS
Negative staining with Indian Ink
-EPS doesn’t stain
2 forms of structures for the EPS
Can be homopolysaccharides ( made up of one sugar component) or heteropolysaccharides (made up of multiple types of sugars)
EPS - 3 ways it functions as a pathogenic determinant
- Inhibits phagocytosis
- formation of adhesions and biofilms
- diffusion barrier to render antimicrobials less effective
How does the EPS inhibit phagocytosis
A. Poor immunogen: body doesn’t easily produce antibodies against slime layers
- vaccines against EPS tend to use conjugation to proteins as they are better immunogens
- uses Hyaluronic acid which is also found in connective tissue
B. Mask other surface components from antibodies & complements.
How does the EPS form adhesions and biofilms
A. EPS provides a means for bacteria to adhere to surfaces
B. EPS forms the matrix of biofilms for things like dental plaque
How does the EPS act as a diffusion barrier
Prevents antimicrobials from reaching the cell and eliciting their mode of action
What is minimum inhibitory concentration (MIC)
The minimum amount of antimicrobial required to prevent growth
What is minimum bacteriocidal concentration?
The minimum amount of antimicrobial required to kill the bacteria
How does rhizobium interact with plants via the EPS?
- Rhizobium adheres to plant cells via its EPS (recognized by a lectin [protein] on plant cells)
- The adherence leads to formation of root nodules.
- In the nodules, Rhizobium fixes N2 from atmosphere and provides N for the plant, in returns the plant provides nutrients (Carbon) for the bacteria.
What is the significance of the EPS of rhizobium?
enriches the soil with nitrate - does the job of a fertilizer
5 other uses of the EPS
- Desiccation protection
- Carbon and energy storage
- Metal (Mg2+) binding
- Bacteriophage receptor
- Industrial uses (Xanthan gum or Dexrtan gum thickeners)
Where does EPS biosynthesis occur?
At the cell membrane
What are the features/name of the lipid carrier used in EPS biosynthesis?
C55 isoprenoid alcohol phosphate, also called undecaprenol phosphate
common carrier for peptidoglycan, LPS EPS, and teichoic acid synthesis
Synthesized from acetyl-coa
Abundant in the cell (10^5 molecules per cell)
Can span the entire membrane
What needs to happen to the sugar molecules before synthesis can begin ?
They need to be coupled to a nucleotide before synthesis can occur
*activated by coupling to UDP
What are the two models of EPS biosynthesis?
- Lipid carrier dependent
2. ATP binding cassette transporter dependent
5 steps of lipid carrier-dependent EPS biosynthesis
- Sugar nucleotides interact with lipid carrier on the inner leaflet of the cytoplasmic membrane
- Sugars are taken up by lipid carrier, nucleotide recycled
- Sugar residues carried to outer membrane and chain formed
- Lipid carrier returns to inner leaflet for another sugar
- complete polysaccharide is translocated to the cell surface
3 steps of ATP binding cassette transporter-dependent EPS biosynthesis
- Sugar residues are polymerized on the inner leaflet of the cell membrane (lipid carrier is possibly involved)
- Complete polysaccharide passes across the cell membrane via an ABC transporter
3*. in gram negative bacteria, the polysaccharide is translocated to the cell surface possibly by the Bayer’s junctions
Bayer’s junctions def.
Zones of adhesion between the inner and outer membranes in gram negative bacteria
- allows for things to exit the cell
- controversial whether or not they exist
EPS synthesis outside the cell membrane
Site of entire synthetic process
glucosyltransferases turn sucrose –> dextran or mutan
fructosyltransferases turn sucrose –> Levan (polyfructose)
What is the structural component that makes up pili/fimbriae ?
Pilins
-each pili has about 1000 major pilin subunits arranged in a helical manner with an axial hole.
The tip of the pilin is made up of minor pilin subunits
