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Chapter 5
Microbial Nutrition
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The Common Nutrient
Requirements
• macroelements (macronutrients)
– C, O, H, N, S, P, K, Ca, Mg, and Fe
– required in relatively large amounts
• micronutrients (trace elements)
– Mn, Zn, Co, Mo, Ni, and Cu
– required in trace amounts
– often supplied in water or in media
components
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Requirements for Carbon,
Hydrogen, and Oxygen
• often satisfied together
– carbon source often provides H, O and
electrons
• autotrophs
– use carbon dioxide as their sole or principal
carbon source
• heterotrophs
– use organic molecules as carbon sources
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Nutritional Types of Microorganisms
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MIXOTROPHY
•chemical energy source (inorganic)
•inorganic H/e- donor
•organic carbon source
Requirements for Nitrogen,
Phosphorus, and Sulfur
• needed for synthesis of important
molecules (e.g., amino acids, nucleic acids)
• nitrogen supplied in numerous ways
• phosphorus usually supplied as inorganic
phosphate
• sulfur usually supplied as sulfate via
assimilatory sulfate reduction
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Sources of nitrogen
•
•
•
•
organic molecules
ammonia
nitrate via assimilatory nitrate reduction
nitrogen gas via nitrogen fixation
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Growth Factors
• organic compounds
• essential cell components (or their precursors)
that the cell cannot synthesize
• must be supplied by environment if cell is to
survive and reproduce
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Classes of growth factors
• amino acids
– needed for protein synthesis
• purines and pyrimidines
– needed for nucleic acid synthesis
• vitamins
– function as enzyme cofactors
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• Bacterial cell membrane: regulates what
moves in and out of the cytoplasm
• Diffusion –concentration gradients > high to
low
• Osmosis – diffusion of water across a
semipermeable membrane
– Isotonic
– Hypertonic
– Hypotonic
Uptake of Nutrients
by the Cell
• Some nutrients enter by passive diffusion
• Most nutrients enter by:
– facilitated diffusion
– active transport
– group translocation
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Passive Diffusion
• molecules move from region of higher
concentration to one of lower concentration
because of random thermal agitation
• H2O, O2 and CO2 often move across
membranes this way
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Facilitated Diffusion
• similar to passive diffusion
– movement of molecules is not energy
dependent
– direction of movement is from high
concentration to low concentration (down
their concentration gradients)
– size of concentration gradient impacts rate of
uptake
• pass through specific transmembrane integral
proteins.
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Facilitated diffusion…
• differs from passive diffusion
– uses carrier molecules (permeases)
– smaller concentration gradient is required for
significant uptake of molecules
– effectively transports glycerol, sugars, and amino
acids
• more prominent in eucaryotic cells than in
procaryotic cells
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•rate of facilitated
diffusion increases
more rapidly and
at a lower
concentration
•diffusion rate
reaches a plateau
when carrier
becomes
saturated
carrier saturation
effect
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Figure 5.1
17
note conformational change
of carrier
Figure 5.2
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Channels create a hydrophilic pore through
which ions diffuse (left)
Carrier proteins change shape in response to a
solute entering the protein, allowing it to be
released on the other side of the membrane
(right proteins)
Active Transport
• energy-dependent process
– ATP or proton motive force used
• moves molecules against the gradient
• concentrates molecules inside cell
• involves carrier proteins (permeases)
– carrier saturation effect is observed
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Active Transport
• Three ways of driving active transport. The
actively transported molecule is shown in
yellow, and the energy source is shown in red.
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ABC transporters
• ATP-binding
cassette
transporters
• observed in
bacteria,
archaea, and
eucaryotes
Figure 5.3
Three types of carrier-mediated transport. This
schematic diagram shows carrier proteins
functioning as:
– uniporters
– Symporters: transport of two substances in the
same direction
– Antiporters: transport of two substances in
opposite directions
antiport
symport
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Figure 5.4
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Figure 5.5
Group Translocation
• molecules are modified as they are
transported across the membrane
• energy-dependent process
• Iron uptake-the organism secretes
SIDEROPHORES that complex with the very
insoluble ferric ion, which is then transported
into the cell
Phosphoenolpyruvate Sugar Phosphotransferase
PTS
CULTURE MEDIA
A culture medium is a preparation used to:
 grow
 transport
 store microorganisms
TYPES OF MEDIA
 Based on Physical Nature
Liquid
Solid (agar)
 Chemical composition
Defined (synthetic): Know all components and
their concentrations
Complex: contain some ingredients of unknown
composition and/or concentration (supplies
amino acids, vitamins, growth factors…..)
 Function
Table 5.4
Table 5.5
Functional types….
General Purpose: support the growth of many
microorganisms
Enriched media: (supplemented by blood, special
nutrients to encourage the growth of fastidious
heterotrophs
Selective media: favor the growth of particular
microorganisms and inhibit the growth of others
Differential media: distinguish between different
groups of bacteria
examples?????
Isolation of Pure Cultures
• A pure culture is a population of cells arising
from a single cell
• Several methods to separate cells on or in an agar
medium, each cell grows into a completely
isolated colony
• A colony: macroscopically visible growth or
cluster of microorganisms on a solid medium
• Colony morphology helps microbiologists identify
bacteria because individual species often form
colonies of characteristic size and appearance
Methods of Isolation of Pure Cultures
• Pour plate: as follows
– dilute a sample to decrease the number of
microorganisms
– mix the dilution with agar,
– pour the mixture into a petri dish
• Spread plate and streak plate methods
separate cells on an agar surface
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Figure 5.9
37
Spread-plate technique
1. dispense cells onto
medium in petri dish
Figure 5.7
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4. spread cells
across surface
2. - 3. sterilize spreader
38
Streak plate technique
inoculating
loop
Figure 5.8
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Figure 5.10a
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Colony growth
• most rapid at edge of colony
– oxygen and nutrients are more available at edge
• slowest at center of colony
• in nature, many microorganisms form biofilms
on surfaces
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