CHAPTER 4

• • Increase in a population of microbes • Due to reproduction of individual microbes • Results in discrete colony or biofilm


  Microbial growth
• Organisms use a variety of nutrients for their

  energy needs and to build organic molecules and

  cellular structures
• Microbes obtain nutrients from variety of sources
• Organisms classified into two groups based on source of carbon

  1. Autotrophs
  2. Heterotrophs
• Organisms classified into two groups based on source of energy

  1. Chemotrophs
  2. Phototrophs
• Plants, algae, cyanobacteria carbon and energy sources

  Photoautotrophs (light + carbon dioxide)
• Photoheterotrophs ( light + organic compounds)


  Green non sulfur bacteria and purple mon sulfur bacteria, some Archaea
• Chemoautotroph (chemical + carbon dioxide)


  Hydrogen, sulfur, and nitrifying bacteria
• Chemo heterotrophs (chemicals + organic compounds)

  Aerobic respiration, anaerobic respiration, fermentation
• Organisms classified into two groups based on source of electrons

  1. Organotrophs
  2. Lithotrophs
• autrotrophs acquire electrons from inorganic molecules


  Lithotrophs
• Oxygen requirements • Oxygen is essential for obligate aerobes • Oxygen is deadly for obligate anaerobes
• Toxic forms of oxygen are highly reactive and excellent oxidizing agents
• Resulting oxidation causes irreparable damage to cells
• molecular oxygen with electrons in higher energy state


  Singlet oxygen
• form from the incomplete reduction of O2

  superoxide radicals
• formed during reactions catalyzed by superoxide dismutase


  Peroxide anion
• result from ionizing radiation and incomplete reduction of hydrogen peroxide

  Hydroxyl radical
• Four toxic forms of oxygen

  1. Singlet oxygen
  2. Superoxide radicals
  3. Peroxide anion
  4. Hydroxyl radical
• Anabolism often ceases because of insufficient nitrogen
• Nitrogen acquired from organic and inorganic nutrients
• All cells recycle nitrogen from amino acids and nucleotides
• Temperature affects three-dimensional structure of proteins
• Lipid-containing membranes of cells and organelles are temperature sensitive

  1. If too low, membranes become rigid and fragile
  2. If too high, membranes become too fluid
• Psychrophiles

  -5 to 20 °C
• Mesophiles

  5 -45 °C
• Thermophiles

  42 -80°C
• Hyper thermophiles 


  66-105°C
• Organisms are sensitive to changes in acidity .

  H+ and OH–

  interfere with H bonding
• Neutrophiles grow best in a narrow range around neutral pH
• Acidophiles grow best in acidic habitats
• Many microbes produce acidic waste products that can accumulate and inhibit their growth
• Two physical effects of water

  1. Osmotic pressure
  2. Hydrostatic pressure
• Pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane


  Osmotic pressure
• Hypotonic solutions have lower solute concentrations
• Hypertonic solutions have greater solute concentrations
• Water exerts pressure in proportion to its depth

  Hydrostatic pressure
• a microbe harms another organism

  Antagonistic relationships
• members of an association receive benefits that exceed those that would result if each lived by itself

  Synergetic relationship
• organisms become interdependent and rarely live outside the relationship


  Symbiotic relationship