Introduction to protists

• protist cells

  • eukaryotes
  • Membrane bound nucleus
  • Organelles/plastids (chloroplast, amyloplast)
  • Some have cell walls (fungi, algae, plants)
  • Many form multicellular structures
  • Divide by classical mitosis
• who discovered protists

  • Antonie van Leeuwenhoek (1632-1723)
  • Father of protozology: infusoria (protists in modern zoological classification), in 1674
  • “animalcules” have great variety of shape and behaviour
• what did hackel do

  • Ernst Häckel (1834-1919): all unicellular eukaryotes.
  • Includes protozoa and eukaryotic, unicellular algae.
  • He invented many words commonly used by biologists today, such as phylum, phylogeny, and ecology
• protist phylogeny

  • Grouped based on general similarities but exhibit a wide range of morphologies and inhabit many different habitats
  • Difficulty with morphological classification: Chlorarachniophytes
• protist similarities

  • All are Eukaryotes
  • All require a water-based environment which can be fresh or marine water, snow, damp soil, animal guts
  • All undergo mitosis
  • Most require the presence of oxygen (some are microaerophilic)
  • Most are unicellular
  • Most are motile
• protists differences

  • How they obtain nutrition
  • Phagocytosis/engulfing prey
  • Photosynthesis
  • Absorption of nutrients
  • Symbiosis
  • How they move
  • Pseudopodia
  • Cilia
  • Flagella
• how are the supergroups of eukaryotes determined

  using sequencing of DNA & phylogenetics
• why study protists

  • Models of multicellularity
  • Majority of eukaryotic diversity
  • very important pathogens
  • Mutualistic symbiosis with other organisms eg Corals
  • Understanding diversity of life
  • Tell us about how eukaryotic life arose
  • Important roles in ecosystems
  • Photosynthesis – 40% of global photosynthate is protist derived
  • Food chain - significant biomass and component of “phytoplankton”
• SAR

  = stramenopiles, alveolates, rhizaria

  • derived from two supergroups
  • chromalveolata
  • rhizaria
• Stramenopiles 

  All have many short hair-like extensions. Chemoorganotrophic and phototrophic members

  Oomycota, golden algae and diatoms
• oomycota

  • Water moulds, have filamentous growth, cellulose cell walls (not chitin)
  • Phytophthora infestans – potato blight
• golden algae

  • Unicellular phototrophs, can form colonies
  • Golden brown colour – chlorophyll c
  • Dinobryon
• diatoms

  • Uncellular algae
  • Over 100,000 species of diatoms
  • Freshwater and marine habitats
  • Cell walls are made of silica dioxide (frustules)
  • Exhibit radial and pennate symmetry
  • Appeared on Earth about 200 million years ago
  • Also used for illuminating road paint and filtering wine, among many other things.
  • Thalassiosira pseudonoma, Phaeodactylum tricornutum
• alveolates

  • Alveolates contain sacs (alveoli) below their plasma membranes
  • All are unicellular
  • Most are (but not all) photosynthetic
  • ciliates, dinoflagellates
• ciliates

  • Possess cilia for motility and to obtain food
  • Has a ciliated oral groove/mouth
  • Has a contractile vacuole to accumulate and expel excess water
  • Have two nuclei (macronucleus and micronucleus)
  • During conjugation two paramecia exchange micronuclei
  • Blepharisma americanum, Paramecium caudatum, Colpidium sp.
• dinoflagellates

  • Mostly marine, photosynthetic (golden brown chloroplasts), free-living or endosymbionts
  • Two flagella (di, flagellate) – equatorial groove (thrust and spin) and longitudinal groove (rudder!)
  • Primary producers of organic matter
  • free-living, endosymbiotic and apicomplexans
• free living dinoflagellate

  • Associated with toxic red tides
  • Algal blooms become so numerous they discolour coastal waters
  • Depletes oxygen/releases toxins causing illness in humans and marine life.
• endosymbiotic dinoflagellate

  • Endosymbiosis with coral
  • Convert light to carbon for the coral
  • Coral provides protection
  • Symbiodinium, Pyrocystis fusformis
• apicomplexans

  • One end (the apex) of the sporozoite, cell contains a complex of organelles specialised for penetrating host cells and tissues.
  • Apicoplast = degenerate chloroplast
  • Obligate parasites of animals
  • Absorb their nutrients
  • Have a complex life cycle with non-motile adult stages
  • Plasmodium sp. – malaria, Toxoplasma – toxoplasmosis, Cryptosporidium - coccoidiosis
• rhizaria

  No rhizarian parasite of human is currently known

  • cercozoa, foraminifera, radiolarians
• cercozoa

  • The Cercozoa are a group of single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level.
  • Cercozoa represent the largest protist biomass in soil
• foraminifera

  • Exclusively marine organisms
  • They form shell-like structures of calcium carbonate (tests)
  • They absorb huge quantities of dissolved CO2 from the water, which they lock into their shells, trapping the carbon when they sink to the deep ocean floor
  • White Cliffs of Dover are formed from fossilized foraminifera tests
  • Xenophyophore (Syringammina fragilissima)
  • Largest single celled organism (20 cm across)
  • Exclusively deep sea
  • Test creates habitat for associated fauna
• radiolarians

  • Mostly marine, heterotrophic organisms
  • Tests are made of silica
  • Name is derived from radial symmetry of tests
• archaeplastida

  • Chloroplasts have structure and pigment similar to plants.
  • Symbionts with protozoa, sponges and cnidarians
  • Some lichens have green algae in them
  • Includes pathogenic species (to dogs)
  • Unicellular – Chlamydomonas
  • Multicellular - Volvox
  • Exist as colonies of 50,000 cells.
  • They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700
• rhodophyta

  • archaeplastida
  • Porphyra spp. - Red Algae
  • Oldest groups of Eukaryotic algae
  • Use phycobiliproteins as accessory pigments
  • Edible and commonly used in foods i.e. dulse/Nori
• excavata

  • discoba, metamonads
  • Classified based on flagellar structure
  • Most basal flagellate lineage
  • Contains free living and symbiotic forms
  • Important human pathogens
• discoba

  Unicellular, flagellated. Have a crystalline rod in their flagella

  • euglenids, kinetoplastids, heteroloboseans
• euglenids

  • Non-pathogenic
  • Mixotrophs: perform photosynthesis when sunlight is available, but heterotrophic when not.
  • Primary flagellate with a unique crystalline rod
  • Short secondary flagellum
  • Mitochondria have distinct disk shaped cristae
  • Cell shape determined by spiraling strips of protein
  • Can phagocytose bacteria
  • Key example: Euglena
• kinetoplastids

  • Unicellular with flagella
  • Some free living.
  • Kinetoplast, a mass of DNA present in their single large mitochondrion
  • Live primarily in aquatic habitats feeding on bacteria
  • Medically important vector-borne pathogens
  • Trypanosoma brucei, Leishmania, Causes African sleeping sickness by invading the CNS
• heteroloboseans

  • Amoeboid but unrelated to loboseans (amoebozoa)
  • Naegleria fowlerii (fatal water born disease)
• metamonads

  Unicellular, flagellated, live in anoxic (low oxygen) environments

  • diplomonads, parabasilids
• diplomonads

  • Have two nuclei of equal size
  • Have mitosomes (lost mitochondria)
  • Giardia lamblia - Causes giardiasis
• parabasilids

  • Contain a parabasal body
  • Have hydrogenosomes (anaerobic)
  • Genomes lack introns, have genome twice the size of human
  • Trichomonas vaginalis
  • Sexually transmitted disease
  • Travels along the mucus-coated lining of the human reproductive and urinary tracts by moving flagella
  • Also occurs in the urethra of males, often without symptoms.
• amoebozoa

  Terrestrial and aquatic protists that use pseudopodia for movement and feeding

  • tubulinea, entamoebas, plasmodial slime moulds, cellular slime moulds
• tubulinea

  • Free-living, inhabit soil and aquatic environments
  • Move by amoeboid movement (cytoplasmic streaming)
  • Can be up to 750µm in size
  • Amoeba proteus
• entamoebas

  • Parasitic amoeba, oral or intestinal tract
  • Entamoeba histolytica
  • Amoebic dysentery
• plasmodial slime moulds

  • Nuclear division without cytokinesis leads to large “coenocytic” cells or plasmodia
  • Similar life cycle to fungi (produce spores)
  • Mass cytoplasmic streaming enables motile, amoeboid movement
  • Live on decaying matter
  • Can be acellular (a single mass of protoplasm) or cellular.
  • Have saprophytic and parasitic lifestyles
  • Physarum polycephalum
• cellular slime moulds

  • Single celled haploid myxamoebae
  • Under nutrient starvation conditions myxamoebae swarm to form a pseudoplasmodium or “slug”
  • Pseudoplasmodia are multicellular
  • Slugs migrate
  • Produce a stalk and sporangium
• opisthokonta

  Comprises metazoans (animals), humans, fungi and several protist lineages.
• choanoflagellates

  • Member of Opistokonts
  • Have single flagella (like sperm cells)
  • Trap bacteria and detritus against the collar of microvilli, where they are engulfed.
  • Last unicellular ancestor of animals
  • Can form colonies of interest to study origin of multicellularity
  • Distributed globally in sea
  • Very little known