MICROBIAL GROWTH NOTES SANG CLASSMATE HAHA

• Microbial Growth


  Increase in number of cells (not the size of cells)

  
• Growing microbes


  • Accumulate into colonies
  • Clumps of cells large enough to be seen without a microscope
• Biofilms


  Formed by microbes in nutrient poor environments
• By understanding the conditions necessary for microbial growth, we can determine how to control the growth of microbes that cause diseases and food spoilage

  
• We can also learn how to encourage the growth of helpful microbes and those we wish to study
• Physical requirements for microbial growth


  • Temperature
  • pH
  • Osmotic pressure
• Chemical requirements for microbial growth


  • Carbon
  • Nitrogen
  • Sulfur
  • Phosphorus
  • Trace Elements
  • Oxygen
  • Organic growth factors
• Temperature


  Most microorganisms grow well at temperature that humans favor, while some thrive at extremes of temperatures
• Temperature range for microbial growth


  Most bacteria grow only within a limited range of temperatures with their maximum and minimum growth temperatures only approx. 30°C apart
• Microbial classification by preferred range of temperature


  • Psychrophiles (cold loving)
  • Mesophiles (moderate temperature)
  • Thermophiles (heat loving)
• Refrigeration is the most common method of food preservation
• Low temperatures


  Decrease microbial reproduction rates
• pH


  Refers to the acidity or alkalinity of a solution
• pH range for bacterial growth


  Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5

  
• Pickled foods


  Preserved from spoilage by acids produced by bacterial fermentation
• Acidophiles


  Microorganisms that tolerate acidity and thrive in lower pH levels
• pH range for molds and yeasts


  They grow over a greater pH range than bacteria, but they have an optimum pH of 5 to 6
• Chemical buffers


  Chemicals added to the growth medium used to neutralize the acids and maintain proper pH
• Osmotic pressure


  Water and microbial nutrition: Microorganisms require water for growth and even obtain almost all their nutrients in solution from the surrounding water
• High osmotic pressure


  When a microbial cell is in hypertonic solution (concentration of solutes is higher than in the cell), cellular water leaks out through the plasma membrane
• Plasmolysis


  Osmotic loss of water causes shrinkage of the cell's cytoplasm, inhibiting the growth of the cell
• Preservation techniques


  High salt or sugar concentrations draw water out of any microbial cells that are present and thus prevent their growth
• Adaptations to different salt concentrations


  • Obligate/extreme halophiles (thrive in high salt concentrations and even require salt for growth)
  • Facultative halophiles (able to grow to salt concentrations up to 2%)
• Low osmotic pressure


  If osmotic pressure is very low as in hypotonic environments (e.g. distilled water), cellular water tends to enter the cell rather than leave it, causing microbes with a weak cell wall to burst (cytolysis)
• Carbon


  The structural backbone of living matter, needed for all the organic compounds that make up a living cell, or provide energy source
• Chemoheterotrophs


  Get most of their carbon from organic materials such as proteins, carbohydrates, and lipids
• Autotrophs


  Derive their carbon from CO2
• Importance of nitrogen, sulfur and phosphorus


  • Protein synthesis (amino acids)
  • DNA & RNA synthesis
  • ATP synthesis
• Nitrogen use and acquisition


  Organisms use nitrogen primarily to form the amino group of the amino acids of proteins and obtain it through decomposition of proteins, acquisition of ammonium ions, and nitrogen fixation
• Sulfur use and acquisition


  Sulfur is used to synthesize sulfur-containing amino acids and vitamins, and is obtained from sulfate ion, hydrogen sulfide, and sulfur-containing amino acids
• Phosphorus use and acquisition


  Phosphorus is essential for the synthesis of nucleic acids and phospholipids, and is found in the energy bonds of ATP, obtained from phosphate ion
• Trace elements


  Elements such as iron, copper, molybdenum, and zinc, required in very small amounts, usually as cofactors for enzymes
• Oxygen use


  Many current forms of life have metabolic systems that require oxygen for aerobic respiration, with O2 as the final electron acceptor
• Classification based on need for O2

  • Obligate aerobes
  • Microaerophiles
  • Facultative anaerobes
  • Aerotolerant anaerobes
  • Obligate anaerobes
• Oxygen is actually toxic in its toxic free radical form, but this is an essential component of phagocytosis, one of the body's most important defenses against pathogens
• Organic growth factors


  Essential organic compounds that an organism is unable to synthesize and must directly obtain from the environment, including vitamins, essential amino acids, and purine and pyrimidines
• Biofilms


  Communities of bacteria that adhere to each other, residing in a matrix made up primarily of polysaccharides, but also containing DNA and proteins

  
• Culture medium


  A nutrient preparation used for the growth of microorganisms in the laboratory
• Inoculum


  Microbes introduced into a culture medium to initiate growth
• Culture


  The microbes that grow and multiply in or on a culture medium