Microbial Nutrition and
Growth
Nutrition = Obtaining Required
Substances from the
Environment
Essential Nutrients Must be
Provided for an Organism to
Survive and Reproduce
Nutrients
• Inorganic nutrients– atoms, ions or
molecules that contains a combination of
atoms other than carbon and hydrogen
– metals and their salts (magnesium sulfate, ferric
nitrate, sodium phosphate), gases (oxygen,
carbon dioxide) and water
• Organic nutrients- contain carbon bonded to
hydrogen and are usually the products of
living things
– methane (CH4), carbohydrates, lipids, proteins,
and nucleic acids
Macronutrients
• Required in Large Quantities
• Play principle roles in cell structure and
metabolism
• Proteins (source of amino acids)
• Carbohydrates
Micronutrients
Needed in Small Amounts – like
Minerals
Points about Bacterial
Cytoplasm
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Mostly water
Large proportion of protein
97% of dry weight is organic matter
96% of bacterial cell is composed of C,
H, N, O, P and S
Challenge for Bacteria
How to get enough nutrients in
forms that they can use to make
cell components
Bacteria Must Make
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Proteins
Carbohydrates
Lipids
Nucleic Acids
Sources of Essential Nutrients
• Carbon – obtain in organic form, or
reduce CO2
• Nitrogen – Fix N2 or obtain as NO3-NO2-, or NH3
• Oxygen – Atmospheric or
dissolved in water
• Hydrogen – Minerals, water,
organic compounds
Nutrient Sources - Continued
• Phosphorous – Mineral
deposits
• Sulfur – Minerals, H2S
• Metal Ions - Minerals
Mineral Nutrients Important in
Microbial Metabolism
• Potassium – essential to protein synthesis
and membrane function
• Sodium – used in some types of cell
transport
• Calcium – cell wall and endospore stabilizer
• Magnesium – component of chlorophyll;
membrane and ribosome stabilizer
• Iron – component of proteins of cellular
respiration
• Zinc, copper, nickel, manganese, etc.
Growth Factors
• Organic compounds that cannot be
synthesized by an organism & must be
provided as a nutrient
– essential amino acids, vitamins
Nutritional Types
• Autotrophs - use CO2, an
inorganic gas as carbon
source
• Heterotrophs - obtain carbon
in an organic form made by
other living organisms
Autotrophs – “Self-Feeding”
• Phototrophs use light
energy to reduce carbon or
make ATP
• Chemotrophs use energy
stored in inorganic chemical
bonds to reduce carbon or
make ATP
Heterotrophs
• Obtain reduced carbon
compounds made by
another organism
• Chemoheterotrophs –
oxidize reduced carbon to
make ATP
Two Kinds of Bacterial
Heterotrophs
• Saprobes – Obtain nutrients
from dead, decaying matter
• Parasites – Feed off a host
organism
Environmental Influences on
Microbial Growth
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Temperature
Oxygen requirements
pH
Barometric pressure
3 Cardinal Temperatures
• Minimum temperature
• Maximum temperature
• Optimum temperature
3 Temperature Adaptation
Groups
1. Psychrophiles – optimum temperature
below 15oC, capable of growth at 0oC
2. Mesophiles – optimum temperature
20o-40oC, most human pathogens
3. Thermophiles – optimum temperature
greater than 45oC
Ecological Groups by Temperature of
Adaptation
Oxygen in the Microbial
Environment
• Oxygen required by aerobic species
(Bacillus, Pseudomonas) but produces
toxic by-products; these species have
efficient de-tox enzymes
• Facultative anaerobes can exist in
presence of oxygen but have no
requirement for it (E. coli,
Staphylococcus, etc.)
Anaerobes – no Need for Oxygen
• Strict anaerobes cannot tolerate
oxygen (Clostridium sp.)
• Aerotolerant anaerobes have atypical
oxygen detox systems (Lactobacillus
sp.)
• Capnophiles require higher CO2
pressures (Neisseria, Brucella, S.
pneumoniae)
pH Effects on Growth
• Acidophiles require low pH
(Thermoplasma)
• Alkalinophiles require high pH
(Proteus)
Osmotic Effects
• Most microbes exist under hypotonic
or isotonic conditions
• Halophiles – require a high
concentration of salt
• Osmotolerant – do not require high
concentration of solute but can tolerate
it when it occurs
Miscellaneous Environmental
Factors
• Barophiles require high environmental
pressure (like deep sea Archae)
• Dehydrated Cell Stages – Spores
• Extreme radiation conditions Dinococcus radiodurans
Ecological Relationships
• Symbiosis – existing together
• Mutualism – both parties benefit
• Commensalism – one party benefits
without impacting the other
• Parasitism – one party benefits at
expense of the other
• Synergism – multiple organisms
working together
Microbial Biofilms
• Biofilms result when organisms attach
to a substrate by some form of
extracellular matrix that binds them
together in complex organized layers
• Dominate the structure of most natural
environments on earth
• Microorganisms communicate and
cooperate in the formation and function
of biofilms – quorum sensing
Ecological Relationships Continued
• Antagonism – one party acts to inhibit
or eliminate the other
• Example of antagonism:
Antibiosis – producing substances toxic
to other organisms
Microbial Growth
Growth of a population at an
exponential rate under optimal
conditions
Stages in Normal Growth
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Lag phase
Exponential/log phase
Stationary phase
Death or decline
Mathematics of Population Growth
Growth Curve
Methods for Monitoring Growth
• Dilution Plating
• Turbidity analysis using
spectrophotometer
• Direct count with hemacytometer
• Optical detection – Coulter Counter
Turbidity
Direct Microscopic Count
Electronic Counting
It is Ideal to Perform Most
Manipulations of a Culture When
it is Growing in Log Phase