Other Bacteria

Question 1

Cyanobacteria:

• cell wall?
• how do they form clusters?
• Gas vesicles?
• Heterocysts?

Answer 1

• peptidoglycan in cell walls, outer and cytoplasmic membranes have LPS structure is similar to standard gram -
• mucilagenous envelopes/sheaths form clusters of cells
• gas vesicles are found in many cyanobacteria to help maintain buoyancy and to keep cell in water column where the light is.
• heterocysts are rounded, enlarged cells. Their is an anoxic environment inside heterocyst, site for N fixation, nitrogenase is sensitive to oxygen.
• Many cyanobacteria display gliding motility

Question 2

Explain the purpose of gas vesicles in cyanobacteria.

Answer 2

• they are made of protein making them rigid, gas permeable and more dense than the rest of the cytoplasm.
• gas vesicles can control how buoyant the cell is. Osmosis differences causes changes such as increased sugar production = increase water in take putting pressure on vesicles causing them to collapse and the bacteria to sink. Weak SL = rise in column

Question 3

Explain photosynthesis in cyanobacteria.

Answer 3

• Thylakoids: intracellular membranes, location of protein complexes involved in photosynthesis and respiratory electron transport chains
• light harvesting pigments such as phycobilins (accessory pigment) and Chlorophyll a: also found in higher plants + b
• have a common ancestor with the endosymbiont that gave rise to chloroplasts

Question 4

What is the deal with Lichens?

Answer 4

• symbiosis with a fungus and a phototrophic organism
• algae or cyanobacteria
• often cyanobacteria that can fix nitrogen
• fungus gains organic matter from photosynthesis
• bacteria or alga gains anchorage, water and inorganic nutrients, protection from desiccation

Question 5

Spirochetes???

Answer 5

• gram-negative, motile and tightly coiled
• treponema: flat wave form
• others are helical such as Borrelia burgdorferii

Question 6

Spirochetes:

- Treponema?

Answer 6

• host associated spirochetes that are commensals or parasites of humans
• many species cause syphilis (T.pallidum)
• some species are commensals in the mouth
• some species found in rumen, ferment plant polysaccharides

Question 7

Describe spirochetes cell structure.

Answer 7

• protoplasmic cylinder enclosed by cell wall and membrane
• outer sheath is flexible made of lipid, protein and carbohydrate (NOT LPS)
• Endoflagella: one or many, located in the periplasm

Question 8

Explain motility in Spirochetes.

Answer 8

• endoflagella are anchored at one end
• motility is by flexing or lashing motion
  L> endoflagella rotate rapidly
  L> protoplasmic cylinder rotates in the opposite direction
  L> cell under torsion
  L> can move in highly viscus gel like medium like connective tissue

Question 9

Chlamydia. Discuss its cell wall and tropism.

Answer 9

- gram neg type cell walls 
L> does not stain with gram stain
L> outer lipopolysaccharide membrane 
L> lacks peptidoglycan 
- obligate parasite 
L> poor metabolic capacities, require biosynthetic intermediates and probably ATP, some of the simplest biochemical capacities of all known bacteria

Question 10

Discuss the Chlamydia trachomatis genome sequencing.

Answer 10

• small genome
• missing genes for biosynthesis of substances supplied by host
• genes for peptidoglycan synthesis and ATP are present
  L> However there is no biochemical evidence for the presence of peptidoglycan
• It is not clear that Chlamydia generates ATP
• some genes acquired by horizontal transfer from eukaryotes

Question 11

Briefly explain chlamydial infections.

Answer 11

• currently one of the leading sexually transmitted diseases
• non specific urethritis -> quite mild and in males it clears up well but in females it can cause scaring
• trachoma (blindness)
• associated with reactive arthritis in males

Question 12

Explain the two body forms in the infection cycle of Chlamydia

Answer 12

1. Elementary body
   - super small
   - rigid cell wall (LPS cross linkages)
   - infectious
   - compact DNA
   - RNA:DNA 1:1
   - metabolically inactive
2. Reticulate body
   - larger
   - fragile cell wall
   - non infectious
   - RNA:DNA 3:1
   - metabolically active
   - encodes a T3SS effectors modify host to control it.

Question 13

Give a run through of the infection cycle of Chlamydia

Answer 13

1. Elementary body attacks the host cell
2. Phagocytosis of elementary body
3. conversion to reticulate body
4. Multiplication of reticulate bodies
5. conversion to elementary bodies
6. release of elementary bodies
   * *be able to draw this and explain

Question 14

Describe Cyanobacteria.
L> troph ?
L> role on early earth
L> common ancestor

Answer 14

• oxygenic phototrophs
• most species are obligate phototrophs
• important in producing O2 in the early earth atmosphere
• have a common ancestor with the endosymbiont that gave rise to chloroplasts
• morphologically diverse
  L> unicellular and filamentous
  -Many cyanobacteria produce potent neurotoxin that can cause poisoning during blooms
• found in terrestrial freashwater and marine habitat.