MICROBIO

• Microbial growth is the increase in cell number, not cell size
• Growing microbes means an increase in population size
• It is important to understand conditions necessary for microbial growth
• Limit growth of microbes that cause disease, food spoilage
• Encourage growth of beneficial microbes
• The requirements for growth are divided into two main categories

  • Physical requirements
  • Chemical requirements
• Physical requirements


  Temperature, pH, osmotic pressure
• Chemical requirements


  Sources of nutrients
• Temperature


  Microbes grow within limited temperature range
• Minimum growth temperature


  Lowest temp at which a species will grow
• Optimum growth temperature


  Temp at which microbe grows best
• Maximum growth temperature


  Highest temp at which growth is possible
• Microbes divided into 5 categories according to temperature range

  • Cold-loving
  • Low-temp loving
  • Moderate-temp loving
  • Heat-loving
  • High-heat loving
• Psychrophiles


  • Can grow below 0°C; optimum at 15°C
  • Usually killed by temp above 20°C
• Psychrotrophs


  • Can grow at 0°C; optimum at 20°C
  • Cause problems with food spoilage, can grow in fridge
  • But grow slow - proper refrigeration helps prevent food spoilage
• Mesophiles


  • Optimum between 25°C to 40°C
  • Many human pathogens grow best at 37°C
  • Human body temp
  • Mesophiles include most common pathogens, food spoilage microbes
• Thermophiles, hyperthermophiles


  • Grow in hot water tank, volcanic hot springs
  • Cannot grow below 45°C - usually not health problem
• pH


  Concentration of H+ ions
• Low pH


  High H+ - acid
• High pH


  Low H+ - alkaline
• Most bacteria


  • Grow near neutral pH, pH 7
• Acidophiles


  • Grow in acidic environments
• Sauerkraut, pickles


  • Products of acidophiles
• Preserved from spoilage by bacterial fermentation
• Molds and yeasts


  • Can grow between pH 5 and 6
• Osmotic pressure


  • Microbes dependent on water to carry nutrients
  • Live in aqueous (water) environments
• Hypertonic environments


  • Causes water to leave cell
  • Growth inhibited due to plasmolysis
• Food preserved by high osmotic pressure


  Add solutes
• Halophiles


  • Can tolerate high osmotic pressure
• Extreme halophiles


  • Require high salt conditions
  • Live in the Dead Sea, salt lakes
• Carbon


  • 2nd most important nutritional requirement (water #1)
  • Structural backbone for ALL organic molecules
• Chemoheterotrophs


  Use organic carbon sources
• Autotrophs


  Use CO2 for carbon
• Nitrogen, sulfur, phosphorous


  Required for synthesis of cell material
• Proteins


  Require nitrogen, sulfur
• DNA, RNA, ATP


  Require nitrogen, phosphate
• Nitrogen is most abundant of these
• Some bacteria use


  • Ammonia (NH4+)
  • Nitrate (NO3-)
• A few bacteria


  • Use nitrogen gas (N2) from atmosphere
  • Called nitrogen fixation
• Trace elements required by microbes

  • Iron (Fe)
  • Copper (Cu)
  • Zinc (Zn)
  • Magnesium (Mg)
  • Molybdenum (Mo)