Protozoa An Overview Kelly Spiller East View High School Georgetown, TX

Taxonomy and Variety Three main characteristics: Eukaryotic Unicellular No cell Wall Subdivided by motility method: Cilia Flagella Pseudopodia

Distribution Require moist environments Lakes, ponds, streams, moist soil, beaches Basis for many aquatic food chains Very few are pathogenic

Morphology They are so diverse that subdivision is shaky. Some have two nuclei, each with a separate purpose. Some have contractile vacuoles to help avoid osmotic rupture All aquatic and pathogenic protozoa have two life stages. Trophozoite – active feeding stage; more vulnerable; occurs in DEFINITIVE HOST Cyst – resting stage; low metabolism and thick capsule; less vulnerable to harsh conditions; occurs in INTERMEDIATE HOST

Nutrition Most are chemoheterotrophic Phagocytize bacteria, decaying matter, other protozoa or host tissues Some are photoautotrophic Photosynthetic Ex. Dinoflagellates and Euglenids

Reproduction Most reproduce asexually A few reproduce sexually Two become gametocytes and then fuse to form a zygote Ciliates like Paramecium reproduce sexually via conjugation (much more complicated than bacterial conjugation)

Classification Broken into 6 taxa based on the 18S rRNA sequences Parabasala Diplomonadida Euglenozoa Alveolates Rhizaria Ameobozoa Use of other taxonomic distinctions (motility type) does not show genetic relationships

Parabasala Lack mitochondria, single neucleus, parabasal body (Golgi-like structure) Ex. Trichomonas: lives in the female vagina if the pH gets too high (basic) it reproduces rapidly and causes inflamation leading to sterility. Spread via intercourse and is asymptomatic in males

Diplomonadida Lack mitochondria, golgi bodies and peroxisomes Seem to be like eukaryotes that lost all their organelles Two equal sized nuclei Multiple flagella Ex. Giardia: - diarrhea-causing pathogen of animals and humans -spread through ingestion of cysts

Euglenozoa (Euglenids and Kinetoplastids) Euglinids: photoautotrophic, unicellular, contain chloroplasts Store food as a unique polysaccharide called paramylon instead of starch (sugar) Red “eyespot” is responsible for triggering phototaxis Kinetoplastids: Contain a large mitochondrion that has a unique region called kinetoplast Ex. Trypanosoma - Sleeping sickness – Trypanosoma brucei - Chagas disease – Trypanosoma cruzi Ex. Leishmania - Leishmaniasis – sand flies

Alveolates (Ciliates, Apicomplexans, Dinoflagellates) Contain small, membrane-bound cavities called alveoli. Purpose of alveoli is unknown All contain tubular mitochondrial cristae Ciliates: Utilize cilia for motility Chemoheterotrophic Two nuclei Ex. Vorticella – cilia create a whirlpool current to direct food in its “mouth” Ex. Balantidium –ONLY PATHOGENIC CILIATE; Balantidium coli; pig is the reservoir species; fecal oral transmission usually through water Ex. Didinium- which eats Paramecium Ex. Paramecium – pond water ciliate

Alveolates continued Apicomplexans: Chemoheterotrophs Pathogens of animals “Apices” allow them to penetrate host cells Ex. Plasmodium – malaria; spread by moquitos Ex. Cryptosporidium – cryptosporidosis or “crypto”; diarrheal disease most common in AIDS patients; fecal oral route of transmission Ex. Toxoplasma – toxoplasmosis; main host is the cat; spread via contaminated meat and/or feces; spread from mother to infant as well

Alveolates cont. Dinoflagellates: Photoautotrophic Used to be grouped as algae but their rRNA showed differently Make up large portion of marine and freshwater plankton Many are bioluminescent Some produce a red pigment = red tide Produce neurotoxins found in some contaminated fish Ex. Pfiesteria = produces and extremely potent neurotoxin; Possible Estuary Associated Syndrom (PEAS)

Rhizaria Move via threadlike pseudopodia Reproduce via binary fission Ex. Foraminifera - Multi-chambered porous shell made of calcium carbonate (like a snail) - Most live attached to grains of sand on ocean floor -Mostly fossilized Ex. Radiolaria -Ornate shells composed of silica -Dead bodies of radiolarians settle to the bottom of the ocean forming ooze that is hundreds of meters thick in some places!

Amoebozoa Distinguished from rhizarians by having lobe-shaped pseudopodia and no shells Free Living Parasitic Forms: Ex. Naegleria and Acanthamoeba Both cause diseases of the eyes and brains in humans swimming in infected waters Ex. Entamoeba Always live inside animals Can produce possibly fatal amebic dysentery

Rhizaria cont. Slime Molds: Ex. Plasmodial (acellular) multi-nucleate body called plasmodium Ex. Cellular Cells aggregate to form pseudoplasmodium but retain individual nature