SW - Bacteriology IV Flashcards
What are the three main functions of the cytoplasmic membrane?
1) Selective permeability – barrier to diffusion of polar & charged molecules in particular
2) Transport – use of transport proteins to accumulate solutes against a 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
What are 3 features of the cell wall in bacteria?
- 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
What are 2 features of the outer membrane in gram-negative bacteria?
- Lipopolysaccharide layer or LPS
- Little structural role but is an effective barrier
What are 4 features related to microbial locomotion?
- 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
What is the composition of bacterial flagella? (4)
- Long, thin appendages – organelles defined by function rather than structure (flagella differ between bacteria/archea/eukaryotes)
- Bacterial flagella are around 20 nm thick, contain the protein flagellin
- Have a helical shape, with the base having a different structure that links to the ‘motor’
- The array of proteins differs between Gram-negative and Gram-positive cells
What are the 5 different names referring to arrangement of flagella?
- Atrichous - no flagellum
- Monotrichous – single flagellum
- Lophotrichous – multiple flagella from the same location, forming a ‘tuft’
- Amphitrichous – a single flagellum at each end
- Peritrichous – numerous flagella around the cell structure
What is chemotaxis?
Chemotaxis is the movement of cells in response to chemical gradients, allowing bacteria to move toward attractants and away from repellents.
- When no attractant is present E. coli switches from direct swimming to tumbling randomly
- In the presence of an attractant E. coli moves through the gradient in the direction of the attractant
Other forms of locomotion (3)
Gliding motility – independent of structures such as flagella, pili and fimbriae
Twitching motility – involves Type IV pili, important in pathogenicity and biofilm formation (e.g. Pseudomonas aeruginosa)
Swarming motility – rapid, coordinated movement. Multicellular behavior
What are 4 features of Fimbriae and Pili?
- 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.
What is a biofilm? (3)
A biofilm is a microbial, sessile community characterised by cells that are:
1) Irreversibly attached to a substratum, interface or to each other.
2) Are embedded in a self-produced matrix of extracellular polymeric substances (EPS), and
3) In comparison to planktonic cells, they exhibit an altered phenotype concerning:
- Growth rate
- Gene transcription
What are the steps in biofilm formation? (6)
1. & 2. Adhesion, reversible & irreversible (Marshall et al 1972).
3. Maturation 1: formation of microcolonies, surrounded by EPS (Sauer et al 2002).
4. Maturation 2: development of a continuous biofilm (Sauer et al 2002).
5. Dispersion and sloughing off; including due to programmed cell death and lytic phage expression or nitric oxide signalling (Webb et al 2003, 2006).
6. Transport of biofilm particles (flocs); dispersed organisms phenotypically similar to planktonic cells (Webb et al 2003).
What is the EPS?
The glue: extracellular polymeric substances (EPS)
- Biofilm cells are embedded in EPS, which fundamentally influences their micro-environment.
How do microorganisms accumulate and bind at surfaces? (2)
- 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.
