Bacterial culture medium

• Phototrophs

  Use radiant/sun energy (plants and alga)
• Chemotrophs

  Require chemical compounds for energy (animals, fungi, protists)
• Both phototrophs and chemotrophs are present in bacteria
• Electron donors

  Organic molecules
• Lithotrophs

  Bacteria that use reduced inorganic compounds as electron donors
• Lithotrophs have been found growing in rock formations thousands of meters below the surface of Earth
• Lithotrophs may outnumber organotrophs and phototrophs in our biosphere due to their volume of distribution
• Organotrophs

  Bacteria that use organic compounds as electron donors
• Types of microbial metabolism

  • Chemo-organotrophs
  • Photo-organotrophs

  
• Autotrophs

  Use CO2 as major or even sole carbon source
• Heterotrophs

  Require organic compounds as their carbon source
• Nutrients required

  • Carbon
  • Oxygen
  • Nitrogen
  • Water
  • Phosphorus
  • Sulphur
  • Metal ions
• Water

  Required by all organisms, must be in aqueous solution before nutrients can enter cells, provides suitable conditions for metabolic reactions, high specific heat provides resistance to temperature changes, required for hydrolytic reactions
• Nitrogen

  Required by all organisms, bacteria can use atmospheric nitrogen, inorganic nitrogen compounds, or organic nitrogen compounds
• Other nutrients

  • Oxygen
  • Sulphur
  • Phosphorus
• Trace elements

  Metal ions like potassium, calcium, magnesium, iron, zinc, copper, manganese, nickel and cobalt, needed at very low concentrations, function as cofactors for enzyme systems
• Vitamins and vitamin-like compounds

  Function as coenzymes or as building blocks for coenzymes, some bacteria can synthesize them, others require them
• Oxygen

  Required for aerobic respiration, a powerful oxidizing agent that can be toxic to cells
• How oxygen harms bacterial cells

  1. Singlet oxygen (1 O -2 )

  2. Superoxide anion or radical (O2-)

  3. Hydrogen peroxide (H2O2)

  4. Hydroxyl radicals (OH-)
• Superoxide dismutase (SOD)

  Enzyme that converts superoxide radical into molecular oxygen and hydrogen peroxide
• Catalase

  Enzyme that converts hydrogen peroxide into water and oxygen
• Peroxidase

  Enzyme that converts hydrogen peroxide into water without producing oxygen
• Obligate aerobes

  Organisms that require oxygen to live
• Microaerophiles

  Grow in lower oxygen concentration, cannot survive if exposed to normal environment
• Facultative anaerobes

  Can use oxygen when present but are able to continue growth by using fermentation or anaerobic respiration when oxygen is not available
• Anaerobes

  Bacteria that are unable to use molecular oxygen for energy-yielding reactions, most are harmed by it
• Aerotolerant anaerobes

  Grow in the presence of oxygen, oxygen has no effect on their growth, are fermentative and cannot use oxygen for growth
• Diffusion

  The phenomenon of molecular movement, in which atoms or molecules move in a gradient from an area of higher density or concentration to an area of lower density or concentration
• Osmosis

  The diffusion of water through a selectively permeable membrane, water will diffuse from the side with higher water concentration to the side with lower water concentration until equalized
• Active transport

  The transport of nutrients against the diffusion gradient or in the same direction as the natural gradient, but at a rate faster than by diffusion alone, requires specific membrane proteins and expenditure of energy
• Endocytosis

  Cell encloses a substance in its membrane, simultaneously forming a vacuole and engulfing the substance
• Phagocytosis

  Endocytosis accomplished by amoebas and white blood cells to ingest whole cells or large solid matter
• Pinocytosis

  Endocytosis of liquids such as oils or molecules in solution
• The scientific control of microbial growth began about 100 years ago
• Pasteur's work on microorganisms led scientists to believe that microbes were a possible cause of disease

  
• In the mid-1800s, Joseph Lister developed the techniques of aseptic surgery to prevent microbial contamination of surgical wounds
• Handwashing is the best way to prevent transmission of pathogens
• A variety of physical methods and chemical agents are developed to control microbial growth outside a host body
• Methods for controlling microbes once infection has occurred, focus mainly on antibiotic chemotherapy
• Sterilization

  The removal or destruction of all living microorganisms