Protists

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• Protists
• simple eukaryotic organisms
• that are not fungi, plants, or animals
• include many lineages of mostly single-celled
  eukaryotes, some distantly related to one
  another
• no single trait is unique to protists

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diplomonads
parabasalids
trypanosomes
euglenoids
radiolarians
foraminiferans
ancestral cells
ciliates
dinoflagellates
Alveolates
apicomplexans
water molds
diatoms
Stramenopiles
brown algae
red algae
Green Algae
chlorophyte algae
charophyte algae
land plants
amoebas
Amoebozoans
slime molds
fungi
choanoflagellates
animals
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Organization and Nutrition

• most protists are single-celled
• but some are colonial or multicellular
• can be autotrophs or heterotrophs
• a few can switch between modes!
• some heterotrophs are beneficial endosymbionts in
  larger organisms
• others are parasites that cause disease

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Autotrophs

• chloroplasts
• evolved in autotrophic protists by two
  mechanisms
• primary endosymbiosis
• cyanobacteria were engulfed by a heterotrophic
  cell and later evolved into chloroplasts
• secondary endosymbiosis
• protists engulfed red or green algae that already
  contained chloroplasts

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Three General Protist Life Cycles

• Protists show great diversity in life cycles
• most reproduce both sexually and asexually
• haploid dominated (zygote is the only diploid
  cell)
• diploid dominated (only gametes are haploid)
• alternation of generations (haploid diploid
  generations)

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Diploid Dominant Cycle
mitosis
single cells or multicelled body
zygote
diploid (2n)
meiosis
fertilization
haploid (n)
gametes
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Haploid Dominant Cycle
zygote
diploid (2n)
meiosis
fertilization
haploid (n)
gametes
haploid cells
single cells or multicelled body
mitosis
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Alternation of Generations
mitosis
multicelled body
zygote
diploid (2n)
meiosis
fertilization
haploid (n)
spores
gametes
multicelled body
mitosis
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What are protists?

• protists do not have a specific defining trait
• they are a collection of many eukaryotic lineages
  rather than a clade
• most protists are single-celled
• but there are multicellular and colonial species
• are autotrophs and / or heterotrophs
• have three types of life cycles

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Flagellated Protozoans

• single-celled protists
• covered by a pellicle made of proteins that help
  cells retain shape
• swim in lakes, seas, and the body fluids of
  animals
• all are entirely or mostly heterotrophic
• life cycle is dominated by haploid cells that
  reproduce by mitosis

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Anaerobic Flagellates

• have multiple flagella and live in oxygen-poor
  waters
• some infect humans and cause disease
• Giardia lamblia intestinal parasite
• Trichomonas vaginalis sexually transmitted
  disease

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Trypanosomes Kinetoplastids

• Kinetoplastids are flagellated protozoans with a
  single large mitochondrion
• Trypanosomes include human pathogens that are
  transmitted by insects
• African sleeping sickness ?Trypanosoma brucei by
  tsetse flies
• Chagas disease ? T. cruzi spread by bloodsucking
  bugs

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Euglenoids

• flagellated protists that do not infect humans
• most prey on bacteria
• some have chloroplasts that evolved from green
  algae and can detect light with an eyespot
• most live in freshwater and have contractile
  vacuoles that expel excess water

flagellum
nucleus
mitochondrion
chloroplast
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contractile vacuole
chloroplast
flagellum
eyespot
nucleus
ER
pellicle
Golgi body
mitochondrion
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What are flagellated protozoans?

• Flagellated protozoans are single-celled protists
  with one or more flagella they are typically
  heterotrophic and reproduce asexually by mitosis
• Some have adapted to life in oxygen-poor waters
  some members of these groups commonly infect
  humans and cause disease
• Trypanosomes include human pathogens that are
  transmitted by insects
• Euglenoids do not infect humans most prey on
  bacteria, but some have chloroplasts that evolved
  from green algae

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Foraminiferans Radiolarians

• single cells with chalky / glassy shells
• live in great numbers in the worlds oceans
• their remains ?limestone, chalk, and chert rocks
• heterotrophs that capture organic debris and tiny
  organisms on cytoplasmic extensions that stick
  out through the shells openings
• a few species of foraminifera and most
  radiolarians are members of the marine plankton
• a collection of mostly microscopic
  organisms that drift / swim in open waters
• planktonic foraminifera radiolarians often have
  smaller photosynthetic protists (diatoms or
  algae) living inside them

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Chalky-Shelled Foraminiferans

• single celled protists that secrete a CaCO3 shell
• helps stabilize atmospheric CO2 levels buffers
  seawater pH
• shells accumulate as chalk or limestone
• most foraminiferans live on the seafloor
• others drift as part of the marine plankton

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Glassy-Shelled Radiolarians

• heterotrophic protists that secrete silica shells
  beneath their plasma membrane
• most are part of the marine plankton
• vacuoles filled with air keep radiolarians afloat
• geologic processes transform silica-rich
  radiolarian ooze into chert

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What are foraminifera radiolarians?

• related lineages of heterotrophic
• single cellular protista
• that live mainly in seawater
• foraminifera make a calcium carbonate shell
• most live on the seafloor, a few are planktonic
• radiolarians have a glassy silica shell
• most are planktonic

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• Three groups of protists
• ciliates
• dinoflagellates
• apicomplexans
• are alveolates having a layer of sacs under the
  plasma membrane

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• Ciliates
• heterotrophic single cellular protista
• move about with the help of cilia
• most ciliates are free-living predators that hunt
  bacteria, other protists, and one another in
  freshwater habitats and the oceans
• e.g. Paramecium cilia - video video 2
• Balantidium coli is a parasite of humans
• reproduce asexually by binary fission or sexually
  by exchanging haploid micronuclei

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prey
prey disappearing into predators oral opening
predator
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contractile vacuole
pellicle
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gullet
cilia
food vacuole (being emptied)
trichocysts
cilium
pellicle
empty contractile vacuole
filled contractile vacuole
alveolus
macronucleus
intact trichocyst
micronucleus
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What are ciliates?

• heterotrophic single cellular protista
• move about with the help of cilia
• most are free-living predators
• but some live inside animals
• Ciliates, Dinoflagellates Apicomplexans, are
  Alveolates group characterized by having tiny
  sacs beneath their plasma membrane

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• Dinoflagellates whirling flagellates
• mostly marine single-celled alveolate protists
• typically have two flagella
• one extends from the base of the cell
• the other wraps around the cells middle
• some are predators or parasites
• others are photosynthetic members of the
  plankton or symbionts in corals

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• Algal blooms
• great increases in free-living photosynthetic
  dinoflagellates or other protists in habitats
  enriched with nutrients such as agricultural
  runoff
• blooms of certain species cause red tides
• that can sicken humans and kill aquatic organisms
• some dinoflagellates toxins kill directly
  Karenia brevis causes neurotoxic shellfish
  poisoning

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Bioluminescent Dinoflagellates
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What are dinoflagellates?

• mostly marine single-celled alveolate protists
• some are predators or parasites
• others are photosynthetic members of plankton or
  symbionts in corals
• algal blooms a population explosion of protists
• can harm aquatic organisms human health

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• Apicomplexans
• parasitic alveolates
• spend part of their life inside host cells
• Plasmodium ? malaria
• Toxoplasma gondii ? toxoplasmosis
• infect a variety of animals worms to insects to
  humans
• life cycle may involve more than one species

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• Malaria
• the most studied apicomplexan disease
• is a major cause of human death
• a female Anopheles mosquito transmits a motile
  infective cell sporozoite to a vertebrate such
  as a human
• fever and weakness start a week or two after a
  bite
• when infected liver cells rupture and release
  merozoites and cellular debris into the
  bloodstream
• symptoms may subside, but continued infection
  harms the body and eventually kills the host

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Evolution of Plasmodium

• Plasmodium is a single-celled protist that causes
  malaria
• Plasmodium-infected blood cells that get into the
  brain can cause blindness, seizures, coma, and
  death
• Mortality from malaria has driven up the
  frequency of sickle-cell anemia alleles (HbS) in
  some human populations
• Plasmodium species that infects humans is
  descended from a parasite that infects gorillas
  in western Africa
• Researchers detected bits of Plasmodium DNA in
  the 3,500-year-old mummy of the Egyptian pharaoh
  Tutankhamun
• Plasmodium manipulates its mosquito and human
  hosts to maximize its own survival

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Life Cycle of Plasmodium
merozoites
mosquito takes up gametocytes or injects
sporozoites
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Toxoplasmosis

• many people infected by Toxoplasma gondii have no
  apparent symptoms
• but toxoplasmosis can be fatal in
  immune-suppressed people, such as those with AIDS
• T. gondii infection during pregnancy can cause
  neurological birth defects in offspring
• most people become infected by eating cysts in
  undercooked meat
• or by contact with cats that prey on rodents
  birds

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• Stramenopiles
• colorless filamentous molds
• photosynthetic single cells
• large seaweeds
• most stramenopiles are autotrophs
• with chloroplasts that contain a brown accessory
  pigment fucoxanthin, along with chlorophylls a
  c
• stramenopile chloroplasts are thought to have
  evolved from a red alga by secondary
  endosymbiosis

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• Water molds oomycotes
• heterotrophs that form a mesh of filaments made
  up of diploid cells with cellulose cell walls
• decompose organic matter in aquatic habitats
• aquatic parasites e.g. Saprolegnia
• infect plants e.g. Phytophthora
• plant destroyers
• an estimated 5 billion crop losses per year

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Saprolegnia on infected fish
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Phytopthora plant destroyers
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• Diatoms
• single-celled or colonial aquatic protists
• have a two-part silica shell and reproduce
  asexually
• most are photosynthetic
• with a brown accessory pigment fucoxanthin
• major components of phytoplankton
• shells accumulate on the seafloor and form
  diatomaceous earth

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http//www.micromagus.net/microscopes/pondlife_pla
nts01.html
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• Brown Algae
• multicellular protists
• live in temperate or cool coastal waters
• 1,500 species range in size from microscopic
  filaments to giant kelps 30 meters (100 feet)
  tall
• some are used commercially as
• thickeners algins
• food
• fertilizer
• herbal supplements
• bladderwrack

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• Giant Kelps
• form forest-like stands in coastal waters of the
  Pacific NW
• kelp life cycle is an alternation of generations
  in which a 2n spore-bearing body is the large,
  long-lived stage
• microscopic gamete-forming bodies form during the
  shorter, haploid stage of the life cycle

bladder
stipe
blade
holdfast
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kelp forest 3 min. video
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• Red algae
• mostly multicellular
• marine algae that live in clear, warm waters
• red accessory pigments phycobilins allow red
  algae to live at greater depths than other algae
• most grow as thin sheets or in a branching
  pattern
• coralline algae has hardened deposits of CaCO3
• have many commercial uses
• agar
• carrageenan
• nori ? Porphyra

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• Green algae
• protists most similar to land plants
• have cellulose in their cell walls
• store sugars as starch
• have chloroplasts descended from cyanobacteria
• include two lineages of photosynthetic,
  single-celled and multicellular species
• chlorophytes
• charophytes

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• Chlorophyte Algae
• the largest lineage of green algae, including
  both freshwater and marine species
• Chlorella - single celled, grown as health food
• Chlamydomonas - single celled, freshwater alga
• Volvox - colonial, freshwater alga
• Cladophora - forms long filaments
• Ulva - sea lettuce
• Codium fragile - branching marine alga

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• Charophyte Algae
• include several lineages of freshwater green
  algae that form a clade with land plants
• some live as single-cells, others form strands of
  cells, and others have a complex body
• Chara stoneworts are the charophyte algae most
  closely related to land plants
• have plasmodesmata
• divide their cytoplasm by cell plate formation

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What are green algae?

• photosynthetic protists
• single cellular or multicellular
• like land plants
• they have cellulose in their cell walls
• store sugars as starch
• have chloroplasts ? from cyanobacteria
• most green algae are chlorophytes
• the smaller group of charophyte algae are the
  closest relatives of the land plants

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Amoebozoans Choanoflagellates

• heterotrophic protista
• closely linked to fungi and animals
• provide clues to how signaling pathways of
  multicellular organisms evolved

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• Amoebozoans
• send out pseudopods
• move about
• capture food
• most have no cell walls, shell, or pellicles
• Amoebas live as single cells
• e.g. Amoeba proteus freshwater predator
• video 1 eating green algae
• video 2 eating Paramecium
• Slime molds are social amoebas
• two types plasmodial cellular slime molds

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• Cellular Slime Molds
• spend most of their lives as individual amoeboid
  cells that feed on bacteria and reproduce by
  mitosis
• when food runs out, thousands of cells form a
  slug that migrates, forms a fruiting body, and
  produces spores and new diploid amoeboid cells
• e.g. Dictyostelium discoideum
• description, pictures short video
• video 3 min in German
• video 12 min

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• Plasmodial Slime Molds
• spend most of their lives as a plasmodium a
  streaming multinucleated mass that feeds on
  microbes and organic matter
• when food supplies dwindle, a plasmodium develops
  into spore-bearing fruiting bodies
• e.g. Physarum video

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• Choanoflagellates
• aquatic, heterotrophic protists
• the closest known protist relatives of animals
• a choanoflagellate cell has a flagellum
  surrounded by a collar of microvilli that sets
  up a current and allows the collar to strain food
  from the water
• sponges, the simplest animals, have similar cells

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What are amoebozoans and choanoflagellates?

• Amoebozoans are a recently recognized lineage
  that includes amoebas and slime molds all are
  unwalled heterotrophs that feed and move by
  extending cytoplasmic extensions (pseudopods)
• Choanoflagellates are flagellated, heterotrophic
  cells that are considered to be close relatives
  of the animals they resemble sponge cells

Diversity of Protists video 22 min.