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)
• Heterotrophs ( different)
• Combination of terms
Photoautotrophs
• Energy(electrons) source-light
• Carbon source-CO2
• Green & purple Sulfur bacteria
Photoheterotrophs
• Energy source-light
• Carbon source –organic cpds
• Green & purple non Sulfur bacteria
Chemoautotrophs
• Energy source is oxidation -reduction
reactions
• Carbon source
• Nitrifying bacteria
Chemoheterotrophs
• Energy & carbon source
• Remove electrons from H in organic cpds
• Final electron acceptor is oxygen
• Final electron acceptor is organic cpd
Physical Requirements for Growth
• Temperature-range
– Psychrophiles
– Psychrotrophs
Temperature
• Mesophiles-25-40C
• Thermophiles-50-60C
• Hyperthermophiles
Determination of Range
• Maximum temperature
• Minimum temperature
• Optimum temperature is closer to max
pH
• Measures acidity or alkalinity
• Bacteria grow best at slightly alkaline pH
• Add buffers to bacterial cultures
• Molds & yeasts lower pH
Osmotic Pressure
• Microbes need water to grow
• Use salt/sugar to preserve food
• Obligate halophiles
• Facultative halophiles
Chemical Requirements for
Growth
• Carbon source-50% of dry weight of cell
• Nitrogen source-amino acids, nucleic
acids
Minerals
• Trace elements
– Small amounts of Fe, Zn, Cu, Co etc.
– Macronutrients-S & P
• Water-medium for chemical reactions
Other Growth Requirements
• Growth factors-essential nutrients
• E. coli needs no growth factors
Other Growth Requirements
• Buffers
• A solidifying agent
Agar Advantages
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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
Oxygen Requirements
• Aerobes
– Use molecular oxygen for respiration
– Superoxide free radicals (O. -)
– Superoxide dismutase- must have
– H2O2 is toxic
Oxygen Requirements
• Facultative anaerobes
Oxygen Requirements
• Obligate anaerobes
Oxygen Requirements
•
Aerotolerants
•
Microaerophiles
Growth of Bacterial Population
• Binary fission or budding
• Generation time-doubling time
Growth Curve
• Lag phase-preparing to grow
• Log phase
• Stationary phase-growth ceases
• Death Phase
Growth of a Colony
• Mass of cells –pure culture
• Some colonies are distinct
• Mixture of cells in different phases of
growth
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
Biofilms
• In nature, microbes in liquid environment
• Cells imbedded in extracellular slime
– Excreted by cells
• Type of defense mechanism
Biofilms
• Quorum sensing
• Important role in infections
• Soaps & disinfectants