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GROWTH OF MICROORGANISMS
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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