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Uptake of nutrients
Cells require nutrients to
grow and survive
Cells possess numerous
transport systems
Must deal with specificity,
transport against conc.
gradient and transport across
selective membrane
Passive vs. facilitated diffusion
Diffusion = movement from
region of high conc. to region
of low conc.
Some molecules can pass
through the membrane
(e.g. H2O, O2, CO2)
 passive diffusion
Passive vs. facilitated diffusion
Many molecules require a
carrier protein (permease) to
cross the membrane
At high conc. permeases are all
occupied (plateau in transport
rate)
Passive vs. facilitated diffusion
Permeases are selective and
only transport closely related
molecules
Permeases span the entire
membrane
Model of facilitated diffusion
Binding of substrate to
permease may induce
conformational change,
releasing molecule in the cell
interior
Permease would then change
back and bind another
molecule
Passive and facilitated diffusion
Both require that nutrient be in
higher conc. outside cell
Prokaryotes usually grow in
nutrient-poor environments
Diffusion more common in
eukaryotes
Active transport and group translocation
Prokaryotes expend energy to transport nutrient against a conc.
gradient
Can use active transport or group translocation
Active transport
ATP-binding cassette (ABC)
transporters
Consist of 2 pore-forming
membrane-spanning domains
Hydrolysis of ATP drives
transport
Active transport
ATP-binding cassette (ABC)
transporters
Often work with periplasmic
(or external) substrate-binding
protein
Transport through outer
membrane is via porins, or
outer membrane
receptors/transporters
Active transport
Proton gradients can drive
active transport
Symport: substrate and proton
both transported into the cell
Antiport: Na+ transported out
as proton enters cell
Uptake of Na+ drives uptake of
nutrient = symport
Group translocation
Molecule is chemically altered
as it is being transported into
the cell
Requires energy
Phosphoenolpyruvate: sugar phosphotransferase system (PTS)
Example of group translocation
Transports various sugars
Consists of two enzymes and a
low molecular weight protein
High energy phosphate
transferred from PEP via
enzymes to sugar molecule
PEP + sugar (outside)  pyruvate + sugar-P (inside)
Iron uptake
Iron is required by almost all
prokaryotes
Siderophores are low
molecular weight iron-binding
molecules secreted by
microorganisms
Either iron or iron-siderophore
complex is transported into cell
by ABC transporters
Iron uptake
Periplasmic iron-binding
proteins and inner membrane
transporters required in gramnegative bacteria
Nutrient requirements
All cells require specific elements to survive
Macroelements
Carbon, Oxygen, Hydrogen, Nitrogen, Sulfur, Phosphate,
Potassium, Calcium, Magnesium and Iron
Nutrient requirements
All cells require specific elements to survive
Macroelements
Carbon, Oxygen, Hydrogen, Nitrogen, Sulfur, Phosphate,
Are components of carbohydrates, proteins, lipids and
nucleic acids
Nutrient requirements
All cells require specific elements to survive
Macroelements
Potassium, Calcium, Magnesium and Iron
Exist as cations in the cell
Play various roles
(e.g. required for enzyme activity)
Nutrient requirements
All cells require specific elements to survive
Trace elements
Manganese, Zinc, Cobalt, Molybdenum, Nickel and
Copper
Contribute to enzyme activity (cofactors)
Carbon requirement
Can be satisfied by organic molecules (also contribute oxygen
and hydrogen)
Organic molecules can also serve as a source of electrons
(energy)
Heterotrophs use organic molecules as their carbon source
Carbon requirement
Can be satisfied by CO2 (oxidized form of carbon)
Reduction of CO2 is energy expensive process
Autotrophs use CO2 as their sole carbon source
Energy source
Can either be from light or the oxidation of organic or inorganic
molecules
Phototrophs obtain energy from light
Chemotrophs obtain energy from oxidations
Electron source
Lithotrophs (rock eaters) obtain electrons from inorganic
molecules
Organotrophs obtain electrons from organic molecules
Nitrogen requirement
Used for the synthesis of various organic compounds
Many microorganisms use amino acids and ammonia
Most phototrophs reduce nitrate to ammonia and then use
ammonia
Some bacteria can reduce and assimilate atmospheric nitrogen
Phosphorus requirement
Required for the synthesis of various cell components like
phospholipids and ATP
Almost all microorganisms can use inorganic phosphate as source
E. coli uses both inorganic and organic sources
Sulfur requirement
Required for the synthesis of cysteine, methionine and some
carbohydrates and vitamins
Most microorganisms use sulfate
Some require cysteine (reduced form of sulfur)
Growth factors
Organic compounds that are required and cannot be synthesized
by the organisms
Amino acids
Purines and pyrimidines
Vitamins
Vitamins
Small organic molecules
Often make up part or all of an enzyme cofactor
Many vitamins are commercially produce using microorganisms
Defined vs. complex culture media
A defined or synthetic medium contains a known amount of
specific chemical components
Defined vs. complex culture media
A complex medium contains some ingredients of unknown
chemical composition
Useful for growing a variety of microorganisms or when growth
requirements of microorganisms are unknown
Agar
Most commonly used solidifying agent
Sulfated polymer of sugars
Extracted from red algae
Selective vs. differential media
Selective media favor the growth of particular microorganisms
Differential media allow for the differentiation between different
bacteria based on biological characteristics
Isolation of pure cultures
Required for the characterization of individual species
Streak plate method
Spread plate method
Pour plate method
(See figures in textbook)
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