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
Granular
cytoplasm
Contractile
vacuole
Nucleus
Food
vacuole
Pseudopodium
Diagrammatic drawing of an amoeba
Amoeba proteus
Diagrammatic drawing of an amoeba
Amoeba proteus
Food
vacuoles
Nucleus
Pseudopodium
Contractile
vacuole
Nomarski differential interference microcopy
Amoeba proteus
Pseudopodia
Phase-contrast microscopy of an amoeba cell
Amoeba
0.1 mm
Food vacuoles
Contractile vacuole
Nucleus
Phase-contrast microscopy of a living amoeba cell
Amoeba proteus
Nucleus
Pseudopodia
Contractile
vacuole
Food vacuoles
Nomarski differential interference microscopy
Amoeba proteus
Pseudopodia
Nucleus
Contractile
vacuole
Phase-contrast microscopy of a living amoeba cell
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
Food vacuole
Pseudopodium
Pseudopodium
Nucleus
Stained Amoeba proteus
Amoeba proteus
Pseudopodia
Nucleus
Food vacuole
Stained Amoeba proteus
Amoeba proteus
C
Stained Amoeba proteus: A, nucleus;
B, Pseudopodia; C, Food vacuole
Entamoeba histolytica – Life Cycle
Entamoeba histolytica – Life Cycle
a
Cyst
b
g
Ingestion by human
of contaminated food
or water
Excretion in faeces
c
f
Encystment in colon
Excystation in small
intestine
d
Trophozoite
e
e
Asymptomatic
colonisation
h
(invasive)
Amoebic colitis
(amoebic)
Liver
abscess
Entamoeba histolytica Trophozoites
Ingested red
blood cells
Nucleus
Ingested red
blood cells
Nucleus
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
Entamoeba histolytica Trophozoites
Nucleus
Stained Entamoeba histolytica trophozoite
with ingested red blood cells (black arrows)
Entamoeba histolytica Trophozoites
Anders Magnusson
Trophozoites with intracellular and
extracellular red blood cells
Entamoeba histolytica - Cysts
Mature
cyst
cb = Chromatid bodies
Nuclei
Amoeboid trophozoites undergo encystment in the
colon due to dehydration of faeces – immature cysts
have two nuclei, mature cysts have four nuclei
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
Nucleus
Trophozoite
Cyst with 4 nuclei
Entamoeba coli
A non-pathogenic Entamoeba
Nucleus
Trophozoite
Cyst has 8 nuclei
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
Sorus
Fruiting
Body
Stalk
Basal disk
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.