Eukaryotic Microbiology (Lectures 22-31)

Apicomplexans (Phylum Apicomplexa) - Structure/ Function

• All parasitic 6000 (gross underestimate probably closer to millions)

• apical complex: used to invade host cell ( 5 organelles, live inside and consume cell)

• gliding motion: powered by contractions of cytoskeletal elements (sooo tiny)

• host cell invasion: protein on parasite surface attach to receptors on host cell surface (many specific)

• parasites quickly (10s) seal itself within parasitophorous vacuole (PV) made out of own lipids

Apical Complex - Elements of invasion

• visible on scanning electrograph microscope

• start feeding on cell lose it, synthesize again when it bursts from cell to then invade another cell

Elements:

• micronemes: fuse with receptors on cell desired for invasion (contain parasite ligands)

• rhoptries: special extrusomes filled with proteins and lipids the contents to make the PV, discharge contents at apical end which break down cell membrane of invaded cell (enzymes)

Apical Complex - Structure

Structure:

• conoid: cone/ collar that wraps around top of microorganism (many microtubules arranged in helical structure, strong and allows for invasion) provides force necessary to help get inside

• polar ring (PR): below conoid almost like enormous basal body, microtubule organizing centre

• subpellicular microtubules: bellow pellicle and line to provide shape and structure going all the way down cell

Apicomplexans - Habitats

Coccidea:

• majority of life being intracellular (WBC,RBC, other blood cells, intestinal cells, mucosa cells, muscle, liver, brain cells)

Gregarines:

• most of life extracellular in the gut

• gut-dwelling species for both groups have cyst “oocyst” stages egg shaped and can withstand harsh environmental conditions

Apicomplexans - Nutrition

• small molecules are taken into the cell at one or more micropores , take up cell contents and phagosomes form as they eat and nutrition goes to parasite (macropinocytosis)

• Malaria parasites ingest haemoglobin (RBC) completely consume in 48 hours burst and invade another RBC

Apicomplexan - Apicoplast

• Ancestral phagocytosis of red algal and turned into choloroplast (secondary symbiont (endosymbiosis)) plastid lives on and parasitic so never going to see the sun… plastid has other metabolic features that the cell needs persisted as colourless plastid…

• genome of ancestral cyanobacterium has reduced to 35 kb

• loss of genes for components of photosynthesis

Membranes:

1. plasma membrane of ancient cyanobacterium

2. cell wall (G-) of ancient cyanobacterium

3. PM of endosymbiotic red alga

4. Phagocytic membrane of apicomplexan

Apicomplexan- Function of apicoplast

• will die without access to ETC target apicoplast

• heme- ferodoxin - fatty acids remove essential part of metabolism and kill parasite by targeting apicoplast

Reproduction/ Life cycle - Sporogony

• follows meiosis

• multiple fission occurs in oocyst to form haploid sporozoites

• sporozoites initiate infection process in (IH) new host

• sporozoites differentiate into trophozoites ones inside cells of IH (lose apical complex once invaded cell)

Reproduction/ Life cycle - Merogony / Schizogony

• multiple fission of trophozoites to form meronts (schizonts) asexual reporoduction

• structures filled with many parasites

• merozoites(unicellular) emerge from meronts (multicellular) and infect new cells

• form trophozoite again after emerging and entering new red blood cells instead of liver cells

• Some form sexual stages

Reproduction/ Life cycle - Gamogony

• formation of gamete producing cells called gametocytes (males/blue and females/pink stain different)

• wait long time till taken up by DH again (male gametes are flagellated, swim around in mosquito to find female gamete and fertilizes)

• forms a zygote

• zygotę immediate undergoes meiosis to initiate sporogony