MBIO 1010 - Lecture 10

• Gas vesicles

  • confer buoyancy in planktonic cells
  • spindle-shaped, gas filled structures made of protein
  • function by decreasing cell density
  • impermeable to water
  • little pockets of gas
  • thrive near the surface
• Gas vesicles are advantageous to cyanobacteria
• Endospores

  • Highly differentiated cells resistant to heat, harsh chemicals and radiation
  • dormant stage of bacterial life cycle
  • ideal for dispersal via wind, water or animal gut
  • help with survival
  • boiling water will not kill the endospores - only autoclaving will as they heat up and add pressure to 121 degrees Celsius
  • long term survival during harsh unfavourable conditions
• Opposite of dormant stage is the vegetative stage
• Endospores are produced only by some gram positives

  • Bacillus sp. - aerobic gram positive rods
  • clostridium sp. anaerobic gram positive rods
• vegetative cell are capable of normal growth - metabolically active
• Endospores are dormant cells formed inside of a mother cell

  • metabolically inactive
  • triggered by lack of nutrients
  • takes about 8-10 hours (huge commitment)
  • E.coli can double in 20 minutes
• Endospore protective features

  • layers
  • spore coat and cortex - protect against chemicals, enzymes, physical damage and heat
  • two membranes - permeability barriers against chemicals
• Protective features of the endospore

  • core
  • dehydrated - protects against heat
  • ca-dipicolinic acid and SASPs (small acid soluble proteins)
  • protect against DNA damage
• Endospores can resist

  • boiling for hours
  • UV, gamma radiation
  • chemical disinfectants
  • dessication
  • age
• Binary fission

  • no mother
  • 2 daughter

  endospore

  • mother
  • no daughter
• Binary fission is symmetrical
• lifecycle of a spore forming bacterium

  • Stage 1: asymmetric cell division
  • DNA replicates
  • identical chromosomes pulled to opposite ends of the cell
• Lifecycle of a spore forming bacterium

  • stage 2: septation
  • Divides into 2 unequal compartments
  • forespores (prespores)
  • mother cell
• lifecycle of a spore forming bacterium

  • stage 3: mother cell engulfs the forespore
  • forespore surrounded by two membranes
• Lifecycle of a spore forming bacterium

  • stage 4: formation of the cortex
  • thick layers of peptidoglycan form between two membranes
  • highly cross-linked layer -core wall
  • loosely cross-linked -cortex (~1/2 of spore volume)
• lifecycle of a spore forming bacterium

  • stage 5: coat synthesis
  • protein layers surround the core wall
  • spore coat
  • exosporium (found in some gram positive)
  • protect the spore from chemicals and enzymes

  calcium, dipicolinic acid and small acid soluble proteins (SASPs) accumulate in the core

  • help stabilize DNA
• Lifecycle of a spore forming bacterium

  • stage 6: Endospore matures
  • core is dehydrated
  • ~10-30% of a vegetative cells water content
• Lifecycle of a spore forming bacterium

  • stage 7: mother cell is lysed
  • mother cell disintegrates
  • mature spore is released
• • Only need 1 to regrow the population
• • Germination is the process that an endospore goes to a vegetative
• • Endospore is for bacteria
• • Endospore are the top of the line resistant
• Flagella and swimming motility

  • hollow protein filaments
  • impart motility
  • must be stained to view
  • flagella stain
  • can be used for identification
  • monotrichous - single flagellum
  • polar or subpolar
  • amphitrichous - flagella at opposite ends
  • lophotrichous - multiple flagella in a single tuft
  • petrichous - flagella distributed around cell
• • Flagellum is the singular
• Flagellar structure

  • Filament
  • Rigid helical protein ~ 20 microm long
  • Composed of identical protein subunits – flagellin2. Hook
  • Flexible coupling between filament and basal body3. Basal Body (motor)
  • Consists of central rod that passes through series of rings:
  • L ring – LPS layer
  • P ring – Peptidoglycan
  • MS ring – Membrane
  • C – ring – Cytoplasm (associated with membrane).