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Phys-Pro - Section 1 > Surface Structure > Flashcards

Surface Structure Flashcards

1
Q

Other names for EPS

A

capsular polysaccharides (CPS), capsule, exopolysaccharides, or glycocalyx

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2
Q

If the EPS is covalently linked to the cell surface it is considered?

A

To be a capsule

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3
Q

If the EPS is loosely associated with the cell surface or free it is considered to be ?

A

A slime layer

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4
Q

Why is the EPS only found in fresh samples of bacteria or bacteria in nature?

A

Because cells grown in the lab experience attenuation

-they no longer need their slime layer growing on the media

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5
Q

What is a method to test for the presence of EPS

A

Negative staining with Indian Ink

-EPS doesn’t stain

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6
Q

2 forms of structures for the EPS

A

Can be homopolysaccharides ( made up of one sugar component) or heteropolysaccharides (made up of multiple types of sugars)

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7
Q

EPS - 3 ways it functions as a pathogenic determinant

A
  1. Inhibits phagocytosis
  2. formation of adhesions and biofilms
  3. diffusion barrier to render antimicrobials less effective
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8
Q

How does the EPS inhibit phagocytosis

A

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.

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9
Q

How does the EPS form adhesions and biofilms

A

A. EPS provides a means for bacteria to adhere to surfaces

B. EPS forms the matrix of biofilms for things like dental plaque

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10
Q

How does the EPS act as a diffusion barrier

A

Prevents antimicrobials from reaching the cell and eliciting their mode of action

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11
Q

What is minimum inhibitory concentration (MIC)

A

The minimum amount of antimicrobial required to prevent growth

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12
Q

What is minimum bacteriocidal concentration?

A

The minimum amount of antimicrobial required to kill the bacteria

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13
Q

How does rhizobium interact with plants via the EPS?

A
  1. Rhizobium adheres to plant cells via its EPS (recognized by a lectin [protein] on plant cells)
  2. The adherence leads to formation of root nodules.
  3. In the nodules, Rhizobium fixes N2 from atmosphere and provides N for the plant, in returns the plant provides nutrients (Carbon) for the bacteria.
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14
Q

What is the significance of the EPS of rhizobium?

A

enriches the soil with nitrate - does the job of a fertilizer

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15
Q

5 other uses of the EPS

A
  1. Desiccation protection
  2. Carbon and energy storage
  3. Metal (Mg2+) binding
  4. Bacteriophage receptor
  5. Industrial uses (Xanthan gum or Dexrtan gum thickeners)
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16
Q

Where does EPS biosynthesis occur?

A

At the cell membrane

17
Q

What are the features/name of the lipid carrier used in EPS biosynthesis?

A

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

18
Q

What needs to happen to the sugar molecules before synthesis can begin ?

A

They need to be coupled to a nucleotide before synthesis can occur

*activated by coupling to UDP

19
Q

What are the two models of EPS biosynthesis?

A
  1. Lipid carrier dependent

2. ATP binding cassette transporter dependent

20
Q

5 steps of lipid carrier-dependent EPS biosynthesis

A
  1. Sugar nucleotides interact with lipid carrier on the inner leaflet of the cytoplasmic membrane
  2. Sugars are taken up by lipid carrier, nucleotide recycled
  3. Sugar residues carried to outer membrane and chain formed
  4. Lipid carrier returns to inner leaflet for another sugar
  5. complete polysaccharide is translocated to the cell surface
21
Q

3 steps of ATP binding cassette transporter-dependent EPS biosynthesis

A
  1. Sugar residues are polymerized on the inner leaflet of the cell membrane (lipid carrier is possibly involved)
  2. 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

22
Q

Bayer’s junctions def.

A

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
23
Q

EPS synthesis outside the cell membrane

A

Site of entire synthetic process

glucosyltransferases turn sucrose –> dextran or mutan

fructosyltransferases turn sucrose –> Levan (polyfructose)

24
Q

What is the structural component that makes up pili/fimbriae ?

A

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

25
Q

What are the structural features of pili?

A

Fine, hair-like proteinaceous appendages.

2 -10 nm in diameter x 0.2 - 10 µm in length.

100 -300 pili/cell (E. coli K12).

26
Q

Which pilin subunit confers its adhesive properties?

A

The minor subunit that constitutes the tip

27
Q

What are the 2 general types of pili

A

Sex pili (F-pili) and General pili

28
Q

Sex pili - role

A

Involved in conjugation and transfer of genetic materials

  • usually only 1-2 molecules per cell
  • ~10 nm in diameter

Not all bacteria have one

29
Q

What is the role of the common pili

A

mediate adherence to host tissue –colonization and biofilm formation, e.g.

30
Q

2 types of common pili

A

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

31
Q

How is the type 1 pili involved in bacterial persistence and infection of the bladder?

A
  • 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
32
Q

What is twitching motility ?

A

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.

33
Q

What is the role of the inner membrane peptidase PilD in type 4 pili assembly

A

To process the major pilin (PilA) and minor pilin proteins

34
Q

What is the role of the hexameric ATPase PilB?

A

To polymerize the major and minor pilin proteins into a helical fibre

35
Q

How is retraction of the pilus acheived?

A

By depolymerization of the protein subunits

-this is done by 2 ATPases: PilT and PilU

36
Q

Which protein forms the secretion pore through which the pilus passes ?

A

PilQ

37
Q

What is an RS layer composed of?

A

proteins or glycoproteins arranged in hexamers, tetramers, or dimers

38
Q

What is the function of an RS layer?

A
  1. Protective barrier
  2. Acts to maintain cell shape in some archaea
  3. Can act as a virulence factor
39
Q

RS layers are common in which 2 kinds of bacteria?

A

Archaea and eubacteria

Phys-Pro - Section 1 (8 decks)

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