bacteriology 4

Question 1

cytoplasmic membrane

Answer 1

controlling diffusion of what goes in and out
Structurally weak but important to provide selective permeability.
Phospholipid bilayer with embedded proteins
hydrophobic and hydrophilic components.

Question 2

cell membrane

Answer 2

provides structural strength, resist osmotic pressure

Question 3

3 main functions of cm

Answer 3

1. Selective permeability – barrier to diffusion of polar & charged molecules in particular.
2. Transport – use of transport proteins to accumulate solutes against concentration gradient. Allow for sufficient nutrients to perform biochemical reactions. Requires energy.
3. Major site of energy conservation & consumption – proton motive force analogous to potential energy in a charged battery.

Question 4

cell wall

Answer 4

Rigid polysaccharide = structural strength.
Strands of peptidoglycan form a sheet around a cell, connected by cross links forming a polymer.
Can be 90% of Gram-positive cell wall.

gram pos have thick layer, neg have thin layer and outer cell mem

Question 5

microbial locomotion

Answer 5

Most bacteria are motile.
Often due to the presence of specific structures; flagella.
Can be due to the presence of gas vesicles – allow regulation of position in water column in some aquatic species.
Some have gliding or twitching or swarming motility.

Question 6

flagella

Answer 6

1. Long, thin appendages – organelles defined by function rather than structure (flagella differ between bacteria/archea/eukaryotes).
2. Bacterial flagella are around 20 nm thick, contain the protein flagellin.
3. Have a helical shape, with the base having a different structure that links to the ‘motor’.
4. The array of proteins differs between Gram-negative and Gram-positive cells.

Question 7

arrangement of flagella

Answer 7

1. Monotrichous – single flagellum.
2. Lophotrichous – multiple flagella from the same location, forming a ‘tuft’.
3. Amphitrichous – a single flagellum at each end.
4. Peritrichous – numerous flagella around the cell structure.

Question 8

chemotaxis

Answer 8

Chemotaxis ofE. coli.(a) When no attractant is presentE. coliswitches from direct swimming to tumbling randomly. (b) In the presence of an attractantE. colimoves through the gradient in the direction of the attractant.

Question 9

gliding motility

Answer 9

1. Gliding motility – independent of structures such as flagella, pili and fimbriae.
2. Twitching motility – involves Type IV pili, important in pathogenicity and biofilm formation (e.g. Pseudomonas aeruginosa).
3. Swarming motility – rapid, coordinated movement. Multicellular behavior.

Question 10

fimbrae and pili

Answer 10

Fimbriae & pili are similar in structure to flagella.
Fimbriae are sometimes referred to as the ‘attachment pili’.
Important in adherence mechanisms.
Pili – two main types; conjugation (sex) pili and type IV pili.

Question 11

biofilm

Answer 11

A biofilm is a microbial, sessile community characterised by cells that are:
Irreversibly attached to a substratum, interface or to each other.
Are embedded in a self-produced matrix of extracellular polymeric substances (EPS), and
In comparison to planktonic cells, they exhibit an altered phenotype with respect to:
Growth rate
Gene transcription

Question 12

life cycle of biofilm

Answer 12

1. & 2. Adhesion, reversible & irreversible (Marshall et al 1972).
2. Maturation 1: formation of microcolonies, surrounded by EPS (Sauer et al 2002).
3. Maturation 2: development of a continuous biofilm (Sauer et al 2002).
4. Dispersion and sloughing off; including due to programmed cell death and lytic phage expression or nitric oxide signalling (Webb et al 2003, 2006).
5. Transport of biofilm particles (flocs); dispersed organisms phenotypically similar to planktonic cells (Webb et al 2003).

Question 13

EPS

Answer 13

Biopolymers of microbial origin
Polysaccharides
Proteins
Glycolipids, phospholipids, LPS
Nucleic acids

Question 14

how do accumulate and bind at surfaces

Answer 14

initial irreversible adhesion

Adhesion at a distance of 5 – 20 nm. A result of forces that operate at long distances, i.e. van der Waals forces.
Little energy needed to remove bacteria, e.g. the kinetic energy produced by turning the flagella leads to desorption

Question 15

irreversible adhesion

Answer 15

Binding is mediated by polymer bridging, achieved by reduced radius of body.
Irreversible binding.
Specific receptor/adhesion based processes.
Can involved specific structural components.
Achieved by bacteria but not colloids, i.e. the DLVO theory no longer helpful.