CHAPTER 18

Life Cycle of Microbial Eukarya

• Endosymbiosis:

  • Focus on endosymbiotic events leading to diverse eukaryotic organisms with membrane-bound nuclei and organelles.

  • complex cells evolved from simpler prokaryotic ancestors, incorporating features such as mitochondria and chloroplasts that are essential for cellular respiration and photosynthesis.

  • 80S ribosomes

  • 70S for mitochondria and chloroplast

• Phylogenetic Tree of eukarya:

• major eukaryotic lineages using 18S rRNA sequences.

Primary Endosybiosis

• no more than 1 or 2 membranes

• mitochondria and chloroplasts acquired

• All eukaryotes descended from an ancestor that contained respiratory mitochondria.

Secondary Endosymbiosis

• eukaryotic cell engulfs another eukaryotic cell that already contains an endosymbiont

• Many protists became phototrophic by acquiring an algal endosymbiont containing chloroplasts.

Diplomonads and Parabasalids (Excavates: single-celled, flagellated eukaryotes)

• Diplomonads:

  • 2 nuclei equal size

  • contain mitosomes (reduced mitochondria lacking electron transport proteins and citric acid cycle enzymes)

  • anaerobic, parasitic lifestyle

  • Giardia intestinalis: A flagellated protozoan, intestinal parasite causing giardiasis, characterized by diarrhea and gastrointestinal distress.

• Parabasalids:

  • No mitochondria

  • use hydrogenosome (anaerobic organelles producing ATP through fermentation) to generate energy

  • Trichomonas vaginalis (sexually transmitted) parasite

• Trypanosomes (excavate)

  • parasitic

  • Trypanosoma brucei causes African sleeping sickness

  • contain membrane flap for nutrient uptake and immune evasion,

  • trypanosome cell characterized by a unique flagellum that aids in motility, and red blood cells

• Euglena/Euglenid (excavate)

  • motile, nonpathogenic, capable of chemoorganotrophic and phototrophic lifestyles (mixotroph)

  • 2 flagella

  • Contain chloroplasts but can lose them in darkness, surviving as chemoorganotrophs.

Paramecium, a Ciliated Protist

Alveolata

Protists: protozoa (eukaryote) (chemoheteroorganotroph or mixotroph)

Algae (photoautotroph)

Fungi: chemoheteroorganotroph

includes 3 major groups:

• Cilliates

  • cilia for motility

• Dinoflagellates

  • mixotroph

  • motility with flagella resembles spinning (dinos = whirling)

  • bioluminescence

  • toxic

  • Acquired photosynthesis through secondary endosymbiosis

• Apicomplexans

  • obligate intracellular nonphototrophic parasites

  • Non-photosynthetic, degenerate chloroplasts

  • nonmotile

  • Plasmodium falciparum (malaria)

  • Toxoplasma gondii (toxoplasmosis)

Diatom frustules

Stramenopiles

• cell walls made of silica called frustules

• unicellular, phototrophic eukaryotes

• pinnate (mirrored) and radial symmetry

Stages of Fruiting Body Formation (Ameobozoa)

1. aggregation of amoebae: Starvation or nutrient depletion.

2. slug migration: as single unit

3. Fruiting body formation: stops migrating, stands upright, and anterior cells form a stalk

4. Mature fruiting body: The stalk cells die, providing structural support.

Fungal Physiology, Structure, and Symbioses

• Physiology

  • heterotrophs: obtian nutrients by secreting enzymes that break down complex organic matter in their environment, allowing them to absorb simpler compounds.

• Fungal Structures:

  • Most fungi are multicellular, forming mycelia and hyphae

    • Mycelia: mass of hyphae

    • Hyphae: thread-like fungal networks. Hyphae extending above the surface can produce asexual spores:

    • Conidia (asexual): which are pigmented and resistant to drying. form at the tips of hyphae called conidiophores

  • their cell walls are primarily made of chitin.

  • They play vital roles in nutrient cycling and can form symbiotic relationships (mycorrhizae) with plants. Help obtain phosphorus and nitrogen

  • mycorrhizae: mutualistic, aid in nutrient uptake

• Reproductive Structures:

  • Fruiting bodies such as mushrooms and puffballs arise from fungi, facilitating spore dispersal and reproduction

  • Mycoses is a disease caused by fungus. can cause athletes foot or histoplasmosis

• Ascomycota Characteristics:

  • Includes genera such as Saccharomyces, Aspergillus, and Candida

  • sexual (mating) and asexual reproduction (conidia).

  • Saccharomyces cerevisiae

    • spherical/oval

    • cell division through budding

    • flourish where sugars are present

  • lifecycle:

    • Alternates between haploid and diploid states.

    • Haploid cells (mating types a & α) fuse to form a diploid cell.

    • Under starvation, diploid cells undergo meiosis, forming ascospores.

Basidiomycota

• Key genera: Agaricus & Amanita

  • basidium: spore-producing structure (haploid basidiospores formed by meiosis)

  • (Agaricus) mushrooms, puffballs, toadstools, yeast, pathogens of plants

  • vegetative and sexual reproduction

  • produce toxin that inhibits RNA polymerase

Archaeplastida and Algae

• Marine Red Algae:

  • Polysiphonia, classified under the Archaeplastida group, showcases adaptations for marine environments.

  • AKA rhodophytes

  • photic zone

  • oxygenic phototrophs

  • red bc of pigment phycoerythrin

• Green Algae:

  • found in marine, freshwater, and terrestrial habitats

  • photic zone

  • chlorophytes contain chlorophyll a & b → can harvest light energy for photosynthesis.

Extra notes

• ignicoccus: interest to researchers studying eukaryotic cells because it has an unusual outer membrane and intermediate compartment that contains membrane-bound vesicles