VJ - Microsporidia

Question 1

What are microsporidia?

Answer 1

Phylum of single-celled eukaryotic organisms, ~1500 species

Question 2

What are 4 features of Microsporidia?

Answer 2

1) Lack mitochondria

• Presence of some mitochondrial genes implies they lost mitochondria when becoming anaerobic

2) Obligate intracellular parasites – highly specialised according to host

3) Small genome (smallest has ~2000 genes; E. coli has ~4500)

4) Spore-forming

Question 3

Describe the structure of the meront (intracellular form)? (4)

Answer 3

• Plasma membrane often with projections (vesicles or tubules) to increase contact surface area with host
• Contain one (monokaryon) or two (diplokaryon) nuclei
• Lots of ribosomes
• No mitochondria!

Question 4

What does the TEM show of a spore? (3)

Answer 4

• Thick wall (protein and chitin layers)
• One or two nuclei
• Rows of circles/ovals are cross-sections of coiled-up polar filament/tube

Question 5

Explain the life cycle of the spore

Answer 5

• Environmental cues trigger germination (osmotic pressure)
• Osmotic pressure in polar vacuole (PV) causes polar filament to pierce host cell
• Spore content (sporoplasm or polaroplasm) injected into host cell (incl. nucleus ‘N’)

Spore -> meront -> sporont -> spore

Question 6

What range of host do microsporidia infect? (4)

Answer 6

As a group, microsporidia infect a wide range of organisms, from ciliates to ‘worms’ to arthropods to fish to mammals

Not known from plants

• Some species have simple life cycle: one host, asexual reproduction
• Other species have complex life cycle: alternating hosts, mixture of asexual and sexual reproduction

Question 7

Describe the Pathogenicity of Microsporidia? (5)

Answer 7

Can infect a wide range of tissues (guts, liver, kidney, brain, muscle, eyes, etc)

• Sometimes cyst-forming (especially in fish)
• Can influence sex determination (arthropods)
• Severity of pathogenicity varies, often more severe in weakened individuals (vertebrates)

Transmission often via environmental spores

Question 8

What is known about immunity against microsporidia?

Answer 8

Limited understanding of how immune system targets microsporidia

• Cellular and non-cellular immunity both play a role
• Haemocytes can become infected themselves (insects)

Part of microsporidian life cycle is intra-cellular!

Question 9

What is microsporidiosis in humans?

Answer 9

Mostly opportunistic infection, in immuno-compromised individuals (e.g. AIDS, organ transplant)

• Can cause intestinal, lung, kidney, brain, sinus, muscle, or eye disease – often chronic