Protists

• Paraphyletic grouping of unicellular and multicellular eukaryotes
• Algae, Protozoa, Slime Molds
• Photosynthetic, Heterotrophic, Mixotrophic
• Various sexual life cycles
• Studied via samples, DNA fragments and overlapping sequence analysis; environmental sequencing/metagenomics
• Studied for…
  • Human Health Concerns (Giardia lamblia, Trypanosome, Malaria)
  • Ecological Issues
    • Primary producers/consumers
    • CO₂ drawdown to benthic reservoirs, outside of atmosphere
    • Algal blooms (red tides, toxins)

Origin of Protists

• Mitochondria: Endosymbiosis Theory
  1. archaeal cell engulfed aerobic bacterium
  2. bacterium survived and formed an endosymbiotic relationship
  3. formation of mitochondria
• Nuclear Envelope: Infolding Hypothesis
  • infolding of plasma membrane surrounded chromosomes
  • created a double membrane with organelles (endoplasmic reticulum)
• Chloroplast: Primary and Secondary Endosymbiosis
  • Primary Endosymbiosis:
    • engulfed cyanobacteria; endosymbiosis theory
    • consider Gram bacteria
      • Gram-positive: thick cell wall of peptidoglycan on the outside
      • Gram-negative: thin cell wall of peptidoglycan with an outer phospholipid bilayer membrane (double membrane wall)
    • food vacuole contained one membrane, then cyanobacterium contained 2 membranes
    • one membrane was lost, resulting in a chloroplast with two bounding membranes
  • Secondary Endosymbiosis:
    • algal cell engulfed by a non-photosynthetic, heterotrophic eukaryote
      • either red or green algae
    • outer membrane of food vacuole, algal cell membrane, and two membranes of cyanobacterium
    • results in up to four membranes around chloroplast
    • also sometimes contains a remnant nucleus from the algal cell: nucleomorph
      • reduced set of genes and often a membrane
    • may have occurred multiple times depending on algaee
  • occurred in Archaeplastida (Plantae)

Eukaryotic supergroups/clade

Excavata

• excavated feeding groove
• Diplomonads, Parabasalids, Eugleenozoans

Archaeplastida

• AKA Plantae supergroup
  • “Ancient plastids” — first evolution of plastids
• Underwent two endosymbiotic events:
  • primary endosymbiosis in all cases
  • secondary endosymbiosis in many cases

Red Algae

Chlorophytes

Charophytes

Stramenophiles

• SAR Supergroup

Diatoms

Water Molds

Brown Algae

Golden Algae

Alveolates

• SAR Supergroup
• Synapomorphic alveoli: membrane sacs inside the cell membrane

Dinoflagellates

• 3um
• modal unicellular organisms
• mostly marine and planktonic
• feeding…
  • ~50% are photosynthetic
  • ~50% lost chloroplast over time
  • some mixotrophic dinoflagellates
• transport…
  • two flagella:
    • one lines the equatorial groove, ribbon flagellum
    • one lines sulcus
    • 90 degrees/perpendicular to each other in most dinoflagellates
  • twirling in water
• armored dinoflagellates… possess hard parts known as thecae
  • thecae are made of cellulose
  • inside alveoli (inside cell membrane)
• pigments:
  • chlorophyll a and chlorophyll c
  • carotenoid
    • distinct reddish-brown coloring
• complex life cycle…
  • resting cysts: protected
  • multiple lifestages
• ecological importance…
  • primary producers as plankton and endosymbionts
  • zooxanthellae are endosymbiotic to corals, sponges, sea anemones, octopus
    • no armor; exchanges materials
    • 30,000 dinoflagellates per cubic millimeter of a coral polyp
    • produces glycerol instead of starch for use in cell respiration
  • red tides are dinoflagellate blooms
    • population explosion
    • 20% dinoflagellate species have toxins
      • assumed to deter predators (copepod zooplankton)
      • aerosolized can kill fish, make people ill/rashed
      • can accumulate in shellfish; bioaccumulation; neurotoxins
  • bioluminescence
    • glows/emits light when disturbed via wave action
      • assumed to protect against predators (cause to be consumed by another consumer)
• Pfiesteria piscicida
  • fish killer in southeast river deltas
  • peduncle: feeding tube
  • amoeboid stage and amoeboid cysts
  • undetected by fish

Apicomplexans

Ciliates

Rhizarians

• SAR Supergroup

Radiolarians

Foraminifera

Cercozoans

Amoebozoa

• Unikonta Supergroup

Slime molds

Tubulinids

Entamoebas

Ophistokonts

• Unikonta Supergroup

Nucleariids

Choanoflagellates

Aquatic Producers/Consumers

• Phytoplankton: photosynthetic, free-floating/swimming surface protists in salt and freshwater; includes some cyanobacteria
• Zooplankton: non-photosynthetic
• Benthic producers are multicellular protists anchored to a substrate in the subtidal or intertidal zones
• Dinoflagellates: endosymbiont protists