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What are Protozoa?
proto = first
zoa = animals
single-celled eukaryotic organisms
Combined Protein Consensus Tree
From S.L. Baldauf (1999)
Am. Nat. 154:S178
What are Protozoa?
proto = first
zoa = plant/animal?
Unicellular eukaryotes
• protozoa
• algae
• yeast/fungi
• slime molds
Protozoan Sizes
Plasmodium
merozoites
Paramecium
Spirostomum
ambiguum
Nummulites
(fossilized)
2-5 m
200-500 m
3 mm
7-13 cm
m = micron = 10-6 meters (1/1000 mm)
Protozoan Life Styles
• absorb solutes (osmotrophy)
• ingest particulates (phagotrophy)
- predation on bacteria or other
protozoa
- pinocytosis (fluid uptake)
• photosynthetic (autotrophy)
• combinations (heterotrophy)
free-living vs. symbiosis
symbiosis
close association of two
different organisms
mutualism
beneficial to both organisms
commensalism
beneficial for one of the
organisms, but the other is
neither benefited nor harmed
parasitism
one organism (the parasite)
living at the expense of the
other (the host)
pathogen
parasites that injure their host
Protozoan Reproduction
Asexual
binary fission
multiple fission
budding
Sexual
fusion of gametes
conjugation
Protozoan
Diversity
• >200,000 named
species
• ~10,000 parasites
• ~20 human
pathogens
Protozoan Motility
Mechanism
Subgroup
ameboid movement
flagella
cilia
gliding motility
amebas
flagellates
ciliates
sporozoa
Protozoan Taxonomy
• confused, controversial and constantly
changing
• originally based on motility (light microscope)
• ultrastructural (electron microscope) criteria
used since 1960’s
• molecular data can help with evolutionary
relationships
• monophyletic groups
• descended from common ancestor
• kinetoplastids, apicomplexa, ciliates
• polyphyletic groups
• multiple ancestors
• amebas and flagellates
Genus + species
What are Protozoa?
• unicellular eukaryote
•?
•?
•?
• extremely diverse
But not simple!