JW - Microbial Adhesion and Biofilm Formation

Question 1

What forces influence microbial adhesion? (2)

Answer 1

• Long-distance forces (5-20nm) – van der Waals (vdW) interactions
• Short-distance forces (0.2-2nm) – More specific interactions, including electrostatic repulsion, polymer bridging, and receptor-ligand binding

Question 2

What are the types of microbial attachment (2) and what are their features (6)?

Answer 2

Reversible attachment

• Occurs at long distances (5-20nm)
• relies on van der Waals forces
• weak binding that can be undone easily

Irreversible attachment

• Occurs at short distances (0.2-2nm)
• involves non-specific and specific binding
• mediated by polymer bridging

Question 3

What is polymer bridging in bacterial adhesion? (2)

Answer 3

• A process where polymer molecules attach to multiple bacterial surface structures, binding them together

Question 4

What polymers are involved in specific irreversible adhesion? (11)

Answer 4

Bacteria possess a range of surface structures that allow for polymer bridging

• exopolymers -exopolysaccharides
• fibrillar proteins
• Fimbriae
• Flagella
• Stalks
• lipoteichoic acids (LTA)
• lipopolysaccharides (LPS)
• surface localised proteins
• surface localised pigments
• A-layers
• S-layers

Question 5

What are the two types of irreversible adhesion?

Answer 5

• Non-specific irreversible adhesion – Involves hydrophobic interactions, ionic, hydrogen, and covalent bonding
• Specific irreversible adhesion (“key-lock”) – Structure-mediated binding that can be blocked by an analogue (e.g., fimbriae-mediated binding)

Question 6

What are some features of fimbriae-mediated binding? (6)

Answer 6

• More common in Gram-negative bacteria
• Large variation in fimbriae structure across species
• Dimensions: 2-10nm width, up to 4um in length
• Consist of identical protein subunits held by H-bonds and hydrophobic interactions
• Flexible fimbriae have many subunits per turn (fibrillae)
• Rigid fimbriae have fewer subunits per turn

Question 7

What are some ecological advantages of fimbriae-mediated binding? (3)

Answer 7

• Gene clusters on plasmids ~10 genes. Allow gene transfer
• Phase variation – Individual cells can switch between expressing and not expressing fimbriae (~1 in 1000 per generation)
• Evasion of host immune responses by altering surface structures

Question 8

Why does key-lock binding often occur on living surfaces? (5)

Answer 8

Epithelial cells expose:

• Lipids (generally glycolipids in cell membrane)
• Proteins (glycoproteins, peripheral & integral proteins)
• Mucus layer (lipids and proteins)

These surfaces present:
Receptor sites (carbohydrates, peptide sequences)

• Carbohydrates (e.g., mannose, di-galactose) – bacteria use adhesins (lectins) to bind to internal sequence in the macromolecular chain
• Peptide sequences - internal and terminal locations

Question 9

How does Vibrio cholerae spread in aquatic environments? (3)

Answer 9

• Piggybacks off zooplankton within the water column
• Colonizes Daphnia pulex (water flea) for transmission
• Mutant cholera (no fimbriae) cannot attach to the zooplankton host

Question 10

What is the role of mshA in Vibrio cholerae adhesion? (2)

Answer 10

• D. pulex colonized with V. cholerae (mshA+) – Can attach via mannose-sensitive haemagglutinin pilin protein
• D. pulex colonized with V. cholerae (mshA-) – Lacks ability to attach properly

mshA - mannose sensitive haemoglutinin
MSHA pilin protein is part of fimbriae