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GROWTH OF MICROORGANISMS. Nutritional Classification. Based upon energy and carbon sources Energy source- electron donors Phototrophs (light nourishment) Photosynthesis. Electron Donors. Chemotrophs Oxidation Reduction Breaking & forming bonds. Carbon Source. Autotrophs (self)

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Nutritional Classification

  • Based upon energy and carbon sources

  • Energy source- electron donors

    • Phototrophs (light nourishment)

    • Photosynthesis


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Electron Donors

  • Chemotrophs

  • Oxidation

  • Reduction

  • Breaking & forming bonds


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Carbon Source

  • Autotrophs (self)

  • Heterotrophs ( different)

  • Combination of terms


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Photoautotrophs

  • Energy(electrons) source-light

  • Carbon source-CO2

  • Green & purple Sulfur bacteria


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Photoheterotrophs

  • Energy source-light

  • Carbon source –organic cpds

  • Green & purple non Sulfur bacteria


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Chemoautotrophs

  • Energy source is oxidation -reduction reactions

  • Carbon source

  • Nitrifying bacteria


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Chemoheterotrophs

  • Energy & carbon source

  • Remove electrons from H in organic cpds

  • Final electron acceptor is oxygen

  • Final electron acceptor is organic cpd


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Physical Requirements for Growth

  • Temperature-range

    • Psychrophiles

    • Psychrotrophs


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Temperature

  • Mesophiles-25-40C

  • Thermophiles-50-60C

  • Hyperthermophiles


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Determination of Range

  • Maximum temperature

  • Minimum temperature

  • Optimum temperature is closer to max


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pH

  • Measures acidity or alkalinity

  • Bacteria grow best at slightly alkaline pH

  • Add buffers to bacterial cultures

  • Molds & yeasts lower pH


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Osmotic Pressure

  • Microbes need water to grow

  • Use salt/sugar to preserve food

  • Obligate halophiles

  • Facultative halophiles


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Chemical Requirements for Growth

  • Carbon source-50% of dry weight of cell

  • Nitrogen source-amino acids, nucleic acids


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Minerals

  • Trace elements

    • Small amounts of Fe, Zn, Cu, Co etc.

    • Macronutrients-S & P

  • Water-medium for chemical reactions


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Other Growth Requirements

  • Growth factors-essential nutrients

  • E. coli needs no growth factors


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Other Growth Requirements

  • Buffers

  • A solidifying agent


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Agar Advantages

  • Few organisms degrade it

  • Liquefies at 100 C

  • Liquid until 40-50 C

  • Lab-keep liquid at 50 C

  • Once solidified, heat to 100 C

  • Gelatin

    • Nutrient for some organisms

    • Liquefies at 35-37 C


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Oxygen Requirements

  • Aerobes

    • Use molecular oxygen for respiration

    • Superoxide free radicals (O. -)

    • Superoxide dismutase- must have

    • H2O2 is toxic


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Oxygen Requirements

  • Facultative anaerobes


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Oxygen Requirements

  • Obligate anaerobes


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Oxygen Requirements

  • Aerotolerants

  • Microaerophiles


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Growth of Bacterial Population

  • Binary fission or budding

  • Generation time-doubling time


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Growth Curve

  • Lag phase-preparing to grow

  • Log phase

  • Stationary phase-growth ceases

  • Death Phase


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Growth of a Colony

  • Mass of cells –pure culture

  • Some colonies are distinct

  • Mixture of cells in different phases of growth


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Growth of a Colony

  • Location within colony determines access to oxygen

  • Surface cells fully aerobic

  • E. coli obtain energy aerobic respiration

  • Embedded cells in center-anaerobic


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Biofilms

  • In nature, microbes in liquid environment

  • Cells imbedded in extracellular slime

    • Excreted by cells

  • Type of defense mechanism


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Biofilms

  • Quorum sensing

  • Important role in infections

  • Soaps & disinfectants


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