MBIO 1010 - Lecture 15

• Complex and defined are mutually exclusive
• Minimal and defined can combine
• Complex an differential can combine
• All minimal are defined but not all defined are minimal
• Differential medium:

  • allows different bacteria to be distinguished
  • everything will grow
  • blood agar - T-soy plate + 5% sheep's blood
  • allows differentiation of hemolytic bacteria (hemolytic - destroying red blood cells - so if all destroyed, no red, has clearance)
  • alpha - incomplete destruction of blood cells (tiny bit of clearing - green in colour)
  • beta - complete destruction
  • gamma - no destruction
  • no hemolysis
  • not hemolytic
  • no zone of clearing
  • no bursting of red blood cells
• Selective medium

  • contain ingredients that inhibit the growth of unwanted microbes
  • allow only specific microbes to grow
  • selects what will grow
  • halotolerant = tolerating high salt
  • can survive higher concentration of salt
  • used to isolate staphylococci from skin
  • differential and selective
  • has mannitol
  • sugar alcohol that some bacteria can ferment
  • Changes the pH - changes the colour from red to yellow
• Enriched medium

  • supplemented with special nutrients to encourage the growth of fastidious bacteria (picky bacteria)
  • complex nutrient requirements - require many growth factors
  • blood agar, chocolate agar (is actually overcooked blood)
  • differential and enriched
• complex vs enriched medium

  • complex - like a basic car, most people can drive it, imagine if someone is like you'll never catch me in one of those, bring me a lambo
  • complex doesn't have to be enriched, and enriched doesn't have to be complex
  • is like the next step up
• Complex example - t-soy agar

  • Don’t know the exact composition

  Blood agar  is t-soy and 5% sheep's blood bringing it up to the enriched category
• Binary fission

  • growth: measured as an increase in the number of cells
  • not like humans (baby to teen to adult)
  • in Mbio we care about the population
  • i have 2 then 4 then 8
• Binary fission

  • cell division following enlargement of a cell to twice its minimum size
  • no remaining mother
• Generation time is the time required for microbial cells to double in number

  • during cell division, each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell
• Generation time = doubling time
• In bacteria and Archaea, growth in cell size, chromosome replication and even septum formation typically occur simultaneously• Contrary to Eukaryotic cells where growth, replication of DNA andseparation via mitosis are separated into interphase and mitosis
• Mitosis does not occur in bacteria and archaea
• most bacteria have shorter generation times than eukaryotic microbes
• generation time is dependent on growth medium and incubation condition: carbon source, pH, temperature
• Exponential growth

  • growth of a microbial population in which cell numbers double at a constant and specific time interval
• a relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth:

  Nt = No x 2^n

  Nt is the final cell number

  No is the initial cell number

  n is the number of generation during the period of exponential growth
• a relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth:

  Nt = No x 2^n

  Nt is the final cell number

  No is the initial cell number

  n is the number of generation during the period of exponential growth
• 2^n is it doubling
• Cells increase exponentially in numbers, the increase in cell number is initially slow but increases at an even faster rate following an exponential curve
• only when plotting on a log scale can one appreciate that the cells are doubling at a constant rate
• log is on the y axis
• x axis is time
• semi log is when only one of the axis is log and one is not
• we are logging the cell number
• When growth is unlimited it is called exponential growth

  • because it generates a curve whose slope increases continuously
• growth rate (k) is the rate of increase in population number or biomass
• since bacteria and archaea grow by binary fission, the growth rate is expressed as the number of doublings per hour
• growth can also be looked as the time it takes for each cell to become 2 cells, this is called the generation time (g)
• open- keep adding in nutrients and removing waste
• closed - not removing anything, ex. test tubes
• growth rate is the generations per time
• generation rate is the growths per time
• growth rate and generation rate are inverse to each other