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
What are the structural features of pili?
Fine, hair-like proteinaceous appendages.
2 -10 nm in diameter x 0.2 - 10 µm in length.
100 -300 pili/cell (E. coli K12).
Which pilin subunit confers its adhesive properties?
The minor subunit that constitutes the tip
What are the 2 general types of pili
Sex pili (F-pili) and General pili
Sex pili - role
Involved in conjugation and transfer of genetic materials
- usually only 1-2 molecules per cell
- ~10 nm in diameter
Not all bacteria have one
What is the role of the common pili
mediate adherence to host tissue –colonization and biofilm formation, e.g.
2 types of common pili
Type 1: expressed by most strains of E. coli, mediats adherence to D-mannose-containing surface receptors on host cells
Type 4: Confers twitching mobility on semisolid surfaces
How is the type 1 pili involved in bacterial persistence and infection of the bladder?
- allows the bacteria to attach to and invade the epithelial lining cells (attachment and invasion)
- The bacteria then replicate in the cells causing them to be shoughed off and exposes the underlying tissue (replication and exfoliation)
- the bacteria can now establish more permanent infection in the underlying tissues
What is twitching motility ?
A jerky translocation (due to constant extension and retraction of the pilus) of the cell across a semi-solid surface
The minor pilin subunit (PilE) on the tip of the type 4 pili mediates adhesion to the host, retraction of the pili allows the bacteria to move along the host surface.
What is the role of the inner membrane peptidase PilD in type 4 pili assembly
To process the major pilin (PilA) and minor pilin proteins
What is the role of the hexameric ATPase PilB?
To polymerize the major and minor pilin proteins into a helical fibre
How is retraction of the pilus acheived?
By depolymerization of the protein subunits
-this is done by 2 ATPases: PilT and PilU
Which protein forms the secretion pore through which the pilus passes ?
PilQ
What is an RS layer composed of?
proteins or glycoproteins arranged in hexamers, tetramers, or dimers
What is the function of an RS layer?
- Protective barrier
- Acts to maintain cell shape in some archaea
- Can act as a virulence factor
RS layers are common in which 2 kinds of bacteria?
Archaea and eubacteria
