Bacterial growth and metabolic pathways

• which bacteria undergo binary fission

  rod shaped bacteria e.g.

  • Escherichia coli
  • Salmonella typhi
  • Pseudomonas aeruginosa
• binary fission process

  1. cell elongation - biomass growth
  2. septum formation - invaginates
  3. completion of septum - formation of walls, cell separation
• equal forms of cell division

  binary fission
• unequal forms of cell division

  • simple budding
  • budding from hyphae
  • cell division of stalked organism
  • polar growth without differentiation of cell size
• MreB

  • actin homologue,
  • bacterial cytoskeleton protein.
  • elongation growth by incorporation of new cell wall material along the longitudinal axis
  • forms elongasome
  • rotation along the inner membrane
  • motion is directly coupled to cell wall synthesis
• FtsZ

  • tubulin homologue (fibres that push away chromosomes in mitosis), cytokinesis ring.
  • Fundamental element of septum formation septum constriction and cell division
  • forms divisome
  • a dynamic ring at midcell 
• Min system (MinCDE)

  • midcell selection.
  • Robust positioning of FtsZ at midcell and only midcell over the lifetime of each cell
• MinC

  • midcell selection through oscillation
  • goes back and forth, most concentrated at poles
  • inhibits formation of FtsZ, ring wont form at the poles
• main factors determining culture growth

  • availability of nutrients
  • presence or absence of oxygen
  • temperature
• obligate aerobes

  need O2
• anaerobes

  no O2
• facultative aerobes

  mostly need O2
• microaerophiles

  need little O2
• aerotolerant anaerobes

  both O2 and no O2
• what happens at minimal temp

  membrane gelling - transport processes so slow that growth cannot occur 
• what happens at optimum temp

  enzymatic reactions occuring at maximal possible rate 
• what happens at maximum temp

  protein denaturation - collapse of the cytoplasmic membrane, thermal lysis
• energy sources

  • phototrophs - light
  • chemotrophs - oxidation of organic or inorganic compounds
• electron sources

  • lithotrophs - reduced inorganic molecules
  • organotrophs - organic molecules
• carbon sources

  • autotrophs - CO2 sole or principle biosynthetic carbon source
  • heterotrophs - reduced organic molecules from other organisms
• process of glycolysis

  1. removes electrons from organic carbon and adds those to NAD making NADH
  2. produces 2 molecules of ATP
  3. generates pyruvate as a key molecule
• process of krebs cycle

  1. oxidation - removal of electrons, more NADH
  2. production of CO2
  3. NADH in electron transport chain
• process of aerobic respiration

  • electrons stored in NADH are transferred into the ETC
  • electrons exit the chain and reduce the terminal acceptor O2 to H2O
  • the membrane is energised by this process as protons are pumped across the membrane to the outside
  • this energy is used to drive oxidative phosphorylation through ATP synthase driven by H+ flux
• anaerobic respiration

  uses other terminal electron acceptors e.g. CO2, NO3-
• nitrification

  • anaerobic conditions

  nitrates → nitrites via nitrate reductase
• fermentation

  • fermentation happens if there is no oxygen as a terminal electron acceptor
  • an organic compound is both the electron donor and acceptor
  • only 2 ATP molecules are generated through substrate level phosphorylation
  • NADH is recycled by reducing pyruvate to lactate and other fermentation products such as ethanol
• homo-fermentative

  lactate is produced
• hetero-fermentative

  mixed products other than lactose are produced
• API tests

  using metabolic information to identify bacteria