Chapter 5

• Algae


  Photosynthetic, eukaryotic organisms
• Algal cells


  • Contain cytoplasm, cell wall (usually), cell membrane, nucleus, plastids, ribosomes, mitochondria, and Golgi bodies
  • Some have a pellicle, a stigma, and/or flagella
• Algae range in size

  • Unicellular microorganisms (e.g., diatoms)
  • Large, multi-cellular organisms (e.g., seaweeds or kelp)
• Some algae may use organic nutrients
• Algae


  • Arranged in colonies or strands
  • Found in fresh and salt water, in wet soil, and on wet rocks
  • Most cell walls contain cellulose
• Algae classified by photosynthetic pigments

  • Green
  • Golden
  • Brown
  • Red
• Algae are an important source of

  • Food
  • Iodine
  • Fertilizers
  • Emulsifiers
  • Stabilizers and gelling agents for jams and culture media
• Prototheca

  A very rare human infection caused by the algal genus protothecosis
• Phycotoxins


  Toxic substances secreted by algae in several genera, poisonous to humans, fish, and other animals
• Paralytic shellfish poisoning


  Disease caused by ingesting phycotoxins produced by dinoflagellates that cause "red tides"
• Protozoa


  Nonphotosynthetic, eukaryotic organisms
• Protozoa


  • Mostly unicellular and free-living
  • More animal-like than plant-like
  • Cannot make their own food, ingest algae, yeasts, bacteria, and smaller protozoa for nutrients
  • Do not have cell walls, but some have a thickened cell membrane called a "pellicle"
• Protozoan life cycle

  • Trophozoite (motile, feeding, dividing stage)
  • Cyst (nonmotile, dormant, survival stage)
• Protozoa divided by locomotion

  • Amoebae (move by pseudopodia)
  • Ciliates (move by cilia)
  • Flagellates (move by flagella)
  • Sporozoa (no visible means of locomotion)
• Protozoa that cause human diseases

  • Entamoeba histolytica (amebic dysentery)
  • Balantidium coli (balantidiasis)
  • Giardia lamblia (giardiasis)
  • Plasmodium spp. (malaria)
• Mycology


  The study of fungi
• Fungi


  • Found virtually everywhere
  • Some are harmful, some are beneficial
  • Include yeasts, moulds, and fleshy fungi (e.g., mushrooms)
  • Are the "garbage disposers" of nature
  • Are not photosynthetic
• Fungal cell walls

  Contain chitin
• Fungal hyphae


  • Some are unicellular
  • Some grow as filaments called hyphae
  • Hyphae intertwine to form a mass called a mycelium
  • Some have septate hyphae (divided into cells by cross walls or septa)
  • Some have aseptate hyphae (no septa)
• Fungal reproduction


  • By budding, hyphal extension, or formation of spores (sexual and asexual)
  • Fungal spores are very resistant structures
• Fungal phyla


  • Zygomycotina
  • Chytridiomycotina
  • Ascomycotina
  • Basidiomycotina
  • Deuteromycotina
• Deuteromycotina or Deuteromycetes


  • Include medically important moulds such as Aspergillus and Penicillium
  • Have no known mode of sexual reproduction or the mode is not known
• Microscopic appearance of various fungi

  • Aspergillus fumigatus
  • Aspergillus flavus
  • Penicillium sp.
  • Curvularia sp.
  • Scopulariopsis sp.
  • Histoplasma capsulatum
• Yeasts


  • Eukaryotic, unicellular organisms that lack mycelia
  • Reproduce by budding, occasionally by spore formation
  • A string of elongated buds is a pseudohypha
  • Some produce thick-walled, spore-like chlamydospores
• Yeasts are found in soil, water, and on the skins of many fruits and vegetables
• Yeasts have been used for centuries to

  Make wine and beer
• Yeasts include

  • Saccharomyces cerevisiae
• Yeasts


  • Eukaryotic, unicellular organisms that lack mycelia
  • Individual cells can only be observed using a microscope
  • Usually reproduce by budding, occasionally by spore formation
  • Can produce thick-walled, spore-like structures called chlamydospores
• Yeast cells

  • Blastospores
  • Blastoconidia
• Pseudohypha


  A string of elongated buds (not really a hypha)
• Yeasts are found in soil and water and on the skins of many fruits and vegetables
• Yeasts used for

  • Wine
  • Beer
  • Baking (Saccharomyces cerevisiae)
• Candida albicans


  • The yeast most frequently isolated from human clinical specimens
• Differentiating yeast colonies from bacterial colonies

  • Yeasts are larger than bacteria and are usually oval-shaped
  • Yeasts are often observed in the process of budding
  • Bacteria do not bud
• Colonies of C. albicans

  • On blood agar
• Gram-stained clinical specimen containing yeasts, bacteria, and white blood cells
• Moulds


  • Produce cytoplasmic filaments called hyphae
  • Aerial hyphae extend above the surface
  • Vegetative hyphae grow beneath the surface
  • Reproduce by spore formation, either sexually or asexually, on the aerial hyphae
• Moulds with commercial importance

  • Produce antibiotics (Penicillium, Cephalosporium)
  • Used to produce large quantities of enzymes
  • Contribute to the flavor of cheeses
• Fleshy fungi


  • Include mushrooms, toadstools, puffballs and bracket fungi
  • Consist of a network of filaments or strands (the mycelium) that grows in soil or on rotting logs
  • The fruiting body that grows above the ground forms and releases spores
  • Some are edible, some are extremely toxic
• Mycoses


  Infectious diseases of humans and animals caused by moulds