Microbial Nutrition
Essential nutrient: Must be provided to an organism (cannot be manufactured) .
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Macronutrient: Needed in large quantities, primarily for cell structure.
Eg. Proteins, carbohydrates
Micronutrient: Needed in small quantities for microbial metabolism. Often serve as cofactors for enzymes. Eg. Magnesium, Zinc
Organic nutrients: Contain both carbon and hydrogen. Organic molecules are living
things or the products of living things. Eg. Sugars, lipids, alcohols.
Inorganic nutrients: Do not contain both carbon and hydrogen. Eg. NaCl, H2O, CO2.
Growth factors: Complex organic nutrients that must be supplied to a cell. Examples include
 Amino acids
 Electron carriers such as NAD and FADH2
 Vitamins
 Complex molecules (hemoglobin)
Growth factors are usually abundant in living organisms but must be added to media in the lab.
How do we describe the adaptive strategies of a cell to its environment?
Prefix
Auto
Hetero
Photo
Sapro
Halo
Thermo
Psychro
Meso
Aero
Anaero
Baro
Eg.
self
other
light
rotten
salt
heat
cold
intermediate
air
no air
pressure
Suffix
troph
phile
bios
tolerant/duric
feed
love
live
survive (but not grow)
Thermophile heat loving
Psychroduric tolerant of cold temperatures
Terms may also be modified:
Obligate/strict
must have a specific set of conditions for survival
Fastidious
Requires specialized growth conditions
Facultative
Able to adapt to a wide range of conditions
Eg.
Facultative anaerobe can live with or without oxygen
Obligate halophile
Can only survive in the presence of a high concentration of salt
Feeding strategies of a cell
Heterotrophs (other feeders): Derive both carbon and hydrogen from other organic compounds. Several
groups exist.
 Saprobes: Digest dead organic matter, usually by exporting digestive enzymes outside the
cell. Obligate saprobes live only in organic matter and are incapable of adapting to a host.
 Facultative parasites: Can be free living (as a saprobe) or can adapt themselves to a host if
needed. Pseudomonas aeruginosa lives in soil and water but also colonizes persons who
have compromised immune systems.
 Obligate parasites: Must grow within a living host. Examples include mycobacterium
leprae, viruses etc.
Autotrophs (self feeders): Derive carbon from atmospheric CO2 and energy from sunlight.
 Algae, photosynthetic bacteria, plants.
Chemical composition of a cell
Water
Proteins
DNA/RNA
Carbohydrates
Lipids
Other
70%
15%
7%
3%
2%
97%
3%
H, O
C, H, N, P, S
C, H, N, P
C, H, O
C, H
The most important elements for metabolism to take place are Sulphur, Phosphorous, Oxygen, Nitrogen,
Carbon, Hydrogen (SPONCH).
Where do nutrients come from?
Carbon sources (Carbohydrates, proteins, lipids, nucleic acids):
Heterotrophs: Primariliy from the bodies of other organisms through decomposition or
parasitism.
Autotrophs: Able to use the carbon in CO2 and convert it into organic compounds.
Nitrogen: Needed for proteins and amino acids. The only usable form of nitrogen is ammonia (NH3) but
some bacteria can convert atmospheric nitrogen (70% of the atmosphere consist of N2) into NH3 in a
process called nitrogen fixation. This ammonia is then used by microbes, plants, animals etc.
Oxygen: Needed for anabolic reactions (synthesis of cell compounds). Primary source is inorganic salts
such as PO4, SO3, NO3
Phosphorous: Required for the synthesis of DNA, RNA and ATP (used for energy). Primary source is
PO4
Sulfur: Needed for the synthesis of amino acids, which are later used synthesize proteins. Primary
sources are SO4, FeS, H2S
Hydrogen: Is needed for the synthesis of everything. Water provides an easy source of this element.
Transport mechanism for nutrient absorption and environmental water concentration:
Passive: No energy required.
Active: Energy is required.
Diffusion: The movement of molecules down their concentration gradient. This is rarely an option for
nutrient absorption as the gradient is not usually in the microbes favor.
Osmosis: The diffusion of water across a semi-permeable membrane, such as a cell membrane. Three
possible conditions exist with regard to the cell and it’s external environment.
Hypotonic solution: The solution outside the cell has a lower concentration of solutes than is
found inside the cell. Net water movement is into the cell by osmosis. Cell walls
Hypertonic solution: The solution outside the cell has a higher concentration of solutes than is
found inside the cell. Net water movement is out of the cell by osmosis. Contractile vacuoles.
Isotonic solution: The solution outside the cell has the same concentration of solutes as that
found inside the cell. There is no net water movement.
Facillitated diffusion: Transmembrane proteins allow specific molecules to diffuse into the cell that
otherwise wouldn’t pass through the membrane. No energy is expended but molecules can only travel
down a concentration gradient. Passive, specific.
Active transport: Energy is expended by the cell to transport nutrients against their gradient, or with the
gradient but faster than they would ordinarily travel. Active, specific.
Bulk transport: The active ingesting of large molecules that occurs when the cell extends a pseudopod
around large molecules, trapping them in a digestive vacuole.
Phagocytosis: Ingestion of solids
Pinocytosis: Ingestion of liquids
Enviromental Influences:
Temperature: Temperatures affect cells because of the effect they have on cellular enzymes.
Lower temperatures reduce the available energy and tend to slow the biochemical reaction
microbes depend on while high temperatures denature enzymes and permanently inactivate them.
Each microbe has a characteristic temperature range which it prefers. For every microbe, three cardinal
temperatures exist: a minimum, below which a microbe won’t grow, a maximum, above which it won’t
grow and an optimum, at which growth occurs most quickly. Bacteria are usually assigned to one of four
groups based on their temperature preferences.
 Psychrophiles:
Optimum below 15°C
 Mesophiles:
Optimum between 10°C and 50°C
 Thermophiles:
Optimum 45°C to 80°C
 Hypertermophiles: Optimum above 80°C
Gas requirement: Some species, called capnophiles, require higher than usual concentrations of
carbon dioxide, anywhere from 3%-10%.
Bacterial species that live in aerobic environments must possess enzymes to deal with the toxic
byproducts of oxygen based metabolism (02-, H2O2, OH-). Two enzymes generally get the job
done.
 Superoxide dismutase converts O2- to H2O2
 Catalase converts H2O2 to H2O and O2
Bacteria with neither of these enzyme systems are obligate anaerobes and are consigned to live
only in completely anaerobic environments. By contrast, facultative anaerobes do not require
oxygen for their metabolism but will generally use it if it is there.
pH: Although exceptions are plentiful, the vast majority of microbes live between pH 6 and pH 8.
Salt concentration: Most bacteria favor about 1% NaCL although obligate halophiles in the
genera Halobacterium and Halococcus require a minimum of 15% NaCl simply to survive. Of
more interest to us are facultative halophiles like Staphylococcus aureus, which can grow
anywhere between 0.1% NaCl and 20% NaCl.
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Relationships Between Microorganisms
All relationships can be described as symbiotic or non-symbiotic
Symbiotic relationships occur between two organisms that are closely linked.
For example they must live at the same time and in the same place.
Three types of symbiotic relationships exist, and are based on who gets the benefits from the
association.
1) Mutualism: Occurs when both organisms benefit. Trichonymphs are protozoans that live within the
gut of termites. Termites eat wood, but cannot digest it; trichonymphs can digest wood but can’t eat it.
By living within the termite (same time and place) both organisms benefit; termites eat the wood,
trichonymphs digest the wood, both share in the nutrients.
2) Commensalism: Occurs when one organism benefits while the other is unharmed by the association.
Satellitism describes the growth of tiny colonies of bacteria next to much larger colonies. In most
cases, the large colony produces a growth factor or other nutrient that the smaller colonies need in order
to grow. Small colony gets nutrients (or growth factors, or whatever), large colony is neither harmed
nor helped.
3) Parasitism: Occurs when one organism benefits at the expense of another. When a virus multiplies
within a host cell, eventually harming the cell, for example.
Non-symbiotic relationships occur when organisms are not as closely linked. Two types exist.
4) Synergism: Occurs when two or more organism cooperate (perhaps unknowingly) to do something
neither could alone. Earlier in the semester I talked about a dead squirrel that seemed to disappear as it
was consumed by fungi. In reality, it might have been a fungus that initiated the breakdown of the hair
and skin, a bacterium that continued breaking down the keratin and other proteins left by the first
fungus and a second fungus that completed the breakdown of the squirrel to its component parts.
Furthermore, this could have taken place over several weeks, as each microbe happened upon the
squirrel.
5) Antagonism: This is competition. Some fungi and bacteria will produce antibiotics that kill other bacteria
(to reduce competition for food, water, nutrients…).