What are Protozoa?

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 SizesPlasmodiummerozoites

2-5 m

Paramecium 200-500 mSpirostomumambiguum

3 mm

Nummulites(fossilized)

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

symbiosisclose association of twodifferent organisms

mutualism beneficial to both organisms

commensalismbeneficial for one of theorganisms, but the other isneither benefited nor harmed

parasitismone organism (the parasite)living at the expense of theother (the host)

pathogen parasites that injure their host

Protozoan Reproduction

Asexualbinary fissionmultiple fissionbudding

Sexualfusion of gametesconjugation

• >200,000 named species

• ~10,000 parasites• ~20 human

pathogens

ProtozoanDiversity

Mechanism Subgroupameboid movement amebas

flagella flagellates

cilia ciliates

gliding motility sporozoa

Protozoan Motility

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!