Amoeboid Protozoa

BY2012 Microbiology Gallery of Amoeboid Protozoa

Amoeboid Protozoa• Unicellular protozoa move and feed by

means of cytoplasmic projections termed pseudopodia

• Amoeboid protozoa are characterised on the form and structure of their pseudopods

• Common in soils and aquatic habitats

• Entamoeba are both pathogens of and commensals in animals

• Dictyostelium (a slime mould) is a amoeba with a complex life cycle involving unicellular and multicellular phases

Amoeba proteus

Pseudopodium

PseudopodiumFood

vacuole

Contractile vacuole

Nucleus

Granular cytoplasm

Diagrammatic drawing of an amoeba

Amoeba proteus

Diagrammatic drawing of an amoeba

Amoeba proteus

Nomarski differential interference microcopy

Nucleus

Contractile vacuolePseudopodium

Food vacuoles

Amoeba proteus

Phase-contrast microscopy of an amoeba cell

Pseudopodia

Amoeba

Phase-contrast microscopy of a living amoeba cell

0.1 mm

Nucleus

Contractile vacuole

Food vacuoles

Amoeba proteus

Nomarski differential interference microscopy

Nucleus

Contractile vacuole

Food vacuoles

Pseudopodia

Amoeba proteus

Phase-contrast microscopy of a living amoeba cell

Contractile vacuole

Nucleus

Pseudopodia

Freshwater amoebae

Phase-contrast microscopy of amoebae

Freshwater amoeba

Phase-contrast microscopy of an amoeba

Freshwater amoeba

Phase-contrast microscopy of an amoeba

Amoeba

Excellent video of amoeba moving (WMV format):

http://www.dr-ralf-wagner.de/Amoeben_Sonnentierchen-englisch.html

Amoeba proteus

Time-lapse photographs of amoebic motility by pseudopod extension

Pfiesteria shumwayae Freshwater amoeba

Pfiesteria shumwayae amoebae engulfing a crytomonad (arrowed) [small freshwater flagellate protozoa] (A) and

showing two engulfed cryptomonads (B)

Metachaos gratum Freshwater amoeba

Nomarski differential interference microcopy

Amoeba proteus

Nucleus

Pseudopodium

Pseudopodium

Food vacuole

Stained Amoeba proteus

Amoeba proteus

Stained Amoeba proteus

Nucleus

Pseudopodia

Food vacuole

Amoeba proteus

Stained Amoeba proteus: A, nucleus; B, Pseudopodia; C, Food vacuole

CC

Entamoeba histolytica – Life Cycle

Entamoeba histolytica – Life Cycle

Ingestion by human of contaminated food

or water

Excystation in small intestine

Excretion in faeces

Encystment in colon

(amoebic) Liver

abscess(invasive)

Amoebic colitis

Asymptomatic colonisation

e e

h

f c

b

Cyst

a

g

Trophozoited

Entamoeba histolytica - Trophozoites

Following ingestion of cysts in faecally contaminated water or food, excystation occurs in the small intestine with the emergence amoeboid trophozoites which migrate to the large intestine

Ingested red blood cells

Ingested red blood cells

Nucleus

Nucleus

Entamoeba histolytica - Trophozoites

Stained Entamoeba histolytica trophozoite with ingested red blood cells (black arrows)

Nucleus

Entamoeba histolytica - Trophozoites

Trophozoites with intracellular and extracellular red blood cellsAnders Magnusson

Entamoeba histolytica - Cysts

Amoeboid trophozoites undergo encystment in the colon due to dehydration of faeces – immature cysts

have two nuclei, mature cysts have four nuclei

Nuclei

Mature cyst

cb = Chromatid bodies

Entamoeba histolytica - Encystment

1 Nucleus 2 Nuclei 4 Nuclei

Entamoeba - Cysts

Nuclei of cysts are arrowed

Entamoeba histolytica Mature Cysts

Nuclei are arrowed

Entamoeba dispar A non-pathogenic Entamoeba

Trophozoite Cyst with 4 nuclei

Nucleus

Entamoeba coli A non-pathogenic Entamoeba

Trophozoite Cyst has 8 nuclei

Nucleus

Life Cycle of Slime Mould Amoeba Dictyostelium

Life Cycle of Slime Mould Amoeba Dictyostelium

Single amoeboid cell Amoebae swarm together “Slug” of amoeboid cells

Dictyostelium discoides is an amoeba that lives in soil and moist leaf litter and belongs to the group termed slime moulds. Dictyostelium spores released from a mature fruiting body germinate forming amoebae. The amoebae feed on bacteria and reproduce by mitosis. When food runs out, the amoebae aggregrate forming a muticellular “slug”. The starvation stress induces expression of cell-cell adhesion glycoproteins on their surfaces, causing the amoebae to stick together.

Life Cycle of Slime Mould Amoeba Dictyostelium

Amoebae within the Dictyostelium slug differentiate, some forming the stalk of the fruiting body while others differentiate at the head of the stalk (sorus) into spores. The fruiting body comprises 50-80,000 cells.

Stalk

Basal disk

Sorus

Fruiting Body