Module 6: Growth

• what are the two methods of isolation?

  simple plating and enrichment culture
• simple plating can isolate colonies, selects for fastest growing/most adapted organism
• cons of simple plating:

  • no medium supports growth of everything
  • competition between microbes
  • hard to select desired microbe
• enrichment culture selects for desired metabolic capacity
• con of enrichment culture: will only grown isolated colonies
• what are the 2 media types?

  differential or selective
• differential: supports growth of many organisms, identify microbes by reaction in medium
• selective: choose ingredient to select against another microbe, favor growth of some microbes
• syntrophy: growth is dependent on another organism
• some microbes are adapted to high or low nutrient levels
• capnophiles require unique environment, increase CO2
• biofilms grow on surfaces
• planktonic grow in liquid suspension
• defined media: know all elements and quantities
• complex media: don't know exact ingredients (ex. yeast extract)
• nutritionally independent: obtain chemicals from environment to make cell needs, many catabolic and anabolic pathways
• cyanobacteria are nutritionally independent
• nutritionally dependent (fastidious): need nutrients and growth factors supplied, often lack anabolic and catabolic pathways
• tuberculosis is nutrient dependent, requires host
• microbe growth: usually increase in numbers, some increase in mass (fungi)
• binary fission: equal division of cells/asexual reproduction
• in binary fissions all cells are clones of the original cell and cell numbers increase exponentially
• cell division: chromosome seperates into 2 cells
• what are the 2 steps of cell division?

  1. ftsz ring forms in the middle
  2. ftsz ring contracts, guiding septum formation
• how does ftsz ring find the middle of the cell?

  • minCD complex assembles at the poles and grows towards the middle, inhibits ftsz
  • minE disassembles minCD from the middle
  • ftsz assembles in the middle at the minCD minimum
• septum formation: ftsZ ring pulls membranes together and separates, build cell wall in between
• what happens to cells that are deficient in ftsz?

  can't septate, form long filaments (apical/growth at ends)
• mreb: directs cell wall synthesis, dictates cell shape
• what happens to mreB when cell isn't growing?

  peptidoglycan blocks mreB cimplex
• what happens to mreB when cell is growing?

  peptidoglycan stretches and forms pores where mreB complex can connect
• what does the mreB complex signal?

  more peptidoglycan for cell wall synthesis
• methods of division:

  1. binary fission
  2. simple budding
  3. budding from hyphae
  4. cell division of stalked organism
  5. polar growth without differentiation of cell size
• all methods of division except for binary fission form unequal products
• what are cons of measuring cell number directly by counting?

  don't know if cells are alive
• methods of measuring cells directly by counting:

  1. microscopic count (petroff-hauser)
  2. particle count (colter counter)
• indirect by plating (viable plate count): dilute sample and count colonies
• indirect by turbidity: measure cell weight by optical density (light scattering)
• batch culture population growth:

  1. lag phase
  2. log phase
  3. stationary phase
  4. death phase
• lag phase: no growth, organism adapting to medium
• log phase: exponential growth