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Microbial Nutrition
The Common Nutrient
Requirements of Microbial
Cells
>95% of dry weight of bacterial cells
is made up of 10 major components
 carbohydrates,
nucleic acids
proteins, lipids,
– Carbon (C)
– Oxygen (O)
– Hydrogen (H)
– Nitrogen (N)
– Sulfur (S)
– Phosphorous (P)
 mg/l
–components
– Potassim (K)
– Calcium (Ca)
– Magnesium (Mg)
– Iron (fe)
Minor components

mcg/l (mg/l) –components
–
–
–
–
–
–
–

Manganese (Mn)
Zinc (Zn)
Cobalt (Co)
Molybdenum (Mo)
Nickel (Ni)
Copper (Cu)
Others (B, Se, …)
Usually enough in water sources to satisfy
requirements
Major nutritional type Sources of energy,
hydrogen/electrons,
and carbon
Representative
microorganisms
Photoautotroph
(Photolithotroph)
Light energy, inorganic
Algae, Purple and
hydrogen/electron(H/e-) donor, green bacteria,
CO2 carbon source
Cyanobacteria
Photoheterotroph
(Photoorganotroph)
Light energy, inorganic H/edonor,
Organic carbon source
Purple nonsulfur
bacteria,
Green sulfur bacteria
Chemical energy source
(inorganic), Inorganic H/edonor, CO2 carbon source
Sulfur-oxdizing
bacteria, Hydrogen
bacteria,
Nitrifying bacteria
Chemical energy source
(organic), Organic H/e- donor,
Organic carbon source
Most bacteria, fungi,
protozoa
II.
Requirements for
Carbon, Hydrogen, and
Chemoautotroph
Oxygen-often satisfied
(Chemolithotroph)
together
Chemoheterotroph
(Chenoorganotroph)
Terms and Definitions:
Categorization based on nutritional
requirements
Carbon Source
Autotroph
CO2 = principle carbon source
Includes photosynthetic bacteria and those capable
of oxidizing inorganic material for energy
generation
Heterotroph
Utilize more reduced and complex carbon sources
derived from other organisms (“nourished by
others”)
Organic compounds used to provide carbon
Prototroph
 Any
microorganism that can synthesize
its nutrients from inorganic material
 Auxotroph
a
mutant organism, especially a
microorganism, that has a nutritional
requirement not shared by the parent
organism
Energy Source
Phototroph
They use the energy from light to carry
out various cellular metabolic processes.
Chemotroph
Chemotrophs
are organisms that obtain energy by the
oxidation of electron donors in their
environments. These molecules can be
organic (chemoorganotrophs) or inorganic
(chemolithotrophs)
Hydrogen or Electron Source
Lithotrophs
Use reduced inorganic compounds as
electron source (“Rock eaters”)
Organotrophs
Use organic compounds as H and electron
donors
Nitrogen
 Amino
acids
 Nucleic acids (purines and
pyrimidines)
 Some carbohydrates and lipids
 Enzyme co-factors
Phosphorous
 ATP
 Co-factors
 Nucleic
acids (phosphodiester
bonds)
 Phospholipids (lipid bilayer)
 Some proteins
Sulfur
 S-containing
amino acids
 Some carbohydrates
 Thiamine
 Biotin
Uptake – Specific
Mechanimsms Utilizing
Selective Permeability
Nutrient
Uptake of nutrition
 Nutrient
molecules frequently cannot
cross selectively permeable plasma
membranes through passive diffusion
and must be transported by one of
three major mechanisms involving the
use of membrane carrier proteins.
• Passive transport / simple diffusion
• Facilitated diffusion
• Active transport
• Group translocation
Passive diffusion
 Passive
diffusion is the process in
which molecules move from a region
of higher concentration to one of
lower concentration as a result of
random thermal agitation. A few
substances, such as glycerol, can
cross the plasma membrane by
passive diffusion.
Facilitated Diffusion
 Requires
large
concentration
gradient for efficient transport
 Differs
from passive diffusion which
utilizes osmosis to achieve transfer
of small substances (glycerol, H2O,
O2, CO2)
 The
rate of diffusion across selectively
permeable
membranes
is
greatly
increased by the use of carrier proteins,
sometimes called permeases, which are
embedded in the plasma membrane.
Since the diffusion process is aided by a
carrier, it is called facilitated diffusion.
The rate of facilitated diffusion increases
with the concentratiotin gradient much
more rapidly and at lower concentrations
of the diffusing molecule than that of
passive diffusion
A model of facilitated diffusion
The membrane carrier can
change conformation after
binding an external molecule
and subsequently release the
molecule on the cell interior. It
then returns to the outward
oriented position and is ready to
bind another solute molecule.
Because there is no energy input, molecules will
continue to enter only as long as their
concentration is greater on the outside.
 Probably
involves a conformational
change
of
carrier
to
deliver
components across the lipid bilayer
– Therefore
material
 Not
effective
for
lipid-insoluble
utilized much by bacteria but it
does occur (e.g glycerol uptake by E.
coli)
Active Diffusion
– Active transport is the transport of solute
molecules to higher concentrations, or
against a concentration gradient, with the
use of metabolic energy input
– Transport
of
molecules
AGAINST
a
concentration gradient
 Material
is more concentrated inside the cell than
the outside
 Ability
to
concentrate
solutes
in
dilute
environments
– Metabolic energy required
 ATP
hydrolysis or
 Proton motive forces (proton gradients generated
by electron transport)
 Types
of active transport
– Symport is the linked transport of two substances
in the same direction
– Antiport is the linked transport of two substances
in opposite directions
Group Translocation
 Group
Translocation
– Transfer of solutes coupled with chemical
modification
– Example:
 Phosphoenolpyruvate
(PEP): Sugar
phosphotransferase system (PTS)
– Sugars are transported ad phosphorylated using
PEP as the phosphate donor
– Glucose, fructose, mannitol, sucrose, N-acetyl
glucosamine, cellobiose, and other solutesn
– PTS proteins cann also serve as chemoreceptors in
chemotaxis
 The
best-known group translocation
system is the phosphoenolpyruvate:
sugar
phosphotransferase
system
(PTS), which transports a variety of
sugars into procaryotic cells while
Simultaneously phosphorylating them
using phosphoenolpyruvate (PEP) as
the phosphate donor.
Simple comparison of transport systems
Items
Passive
diffusion
Facilitated
diffusion
Active
transport
Group
translocation
carrier
Non
Yes
Yes
Yes
transport
speed
Slow
Rapid
Rapid
Rapid
against
gradient
Non
Non
Yes
Yes
transport
molecules
No specificity
Specificity
Specificity
Specificity
metabolic
energy
No need
Need
Need
Need
Solutes
molecules
Not changed
Changed
Changed
Changed
proteins