lecture 2

• Endosymbiosis


  The process by which one organism lives inside another organism, often leading to the evolution of new organelles
• Eukaryotic organelles


  • Derived from endosymbiosis with bacteria and archaea
  • Have enzymes, transporters, and ribosomes homologous to those in bacterial cells
  • Have their own circular DNA chromosomes
  • Divide by binary fission like bacteria
• Origin of eukaryotes


  1. Archaeal ancestor evolves a nucleus

  2. Mitochondrion gained by endosymbiosis with aerobic bacterium

  3. Plastid gained by endosymbiosis with cyanobacterium in plant ancestors
• Microbiome


  All the microorganisms found in a given habitat, including bacteria, archaea, fungi, algae, and other unicellular eukaryotes
• Horizontal transmission


  Microbiome acquired from the environment
• Vertical transmission


  Microbiome passed down directly from parent to offspring
• The average human body contains about 56% microbial cells compared to human cells
• Prokaryotic communities


  • Metabolite cross-feeding
  • Filamentous chains
  • Biofilms
  • Quorum sensing
• Quorum sensing


  • Bacillus cereus (food poisoning)
  • Staphylococcus aureus (infections)
  • Pseudomonas aeruginosa (lung infections)
• Fungi


  • Heterotrophs that engage in absorptive nutrition by secreting enzymes to digest food externally
  • Can be unicellular or multicellular with chitin-rich cell walls
  • Store carbon as glycogen, not starch
  • Have a life cycle including spores
• Fungal hyphae and mycelium


  • Hyphae are the filamentous structures that make up the mycelium
  • Mycelium is the network of hyphae
  • Growth is indeterminate with no defined end structure
  • Cytoplasmic streaming distributes resources through the mycelium
• The largest known fungal organism is an Armillaria ostoyae (honey fungus) mycelium in Oregon that is estimated to be over 8,000 years old, weigh over 35,000 tons, and span 3.5 square miles