Nutritional and Metabolic Diversity
Prokaryotes can be grouped into four categories according
to how they obtain energy and carbon.
Autotrophs are organism that can make their own food from
inorganic sources.
Heterotrophs are organisms that require other organisms in
order to obtain organic molecules.
1. A Photoautotroph uses light as its energy source, and
CO2 as its inorganic source of carbon. Photosynthetic
prokaryotes, include cyanobacteria, plants, certain
protists (algae)
2. A Chemoautotroph derives all of its energy from the
oxidation of inorganic chemicals. They can the make their
organic molecules from the inorganic source such as CO2.
3. A Photoheterotroph is an organism that derives its
energy from light but requires organic compounds in order
to build its own organic material.
4. A Chemoheterotrophs consumes organic molecules for both
energy and organic compounds. Nutritionally,
chemoheterotrophs are either saprobes or parasites.
Bacteria are called decomposers because they break down
organic material and have a role in digesting sewage and
oil, production of alcohol, vitamins, antibiotics, and
genetic engineering.
Saprobes are decomposers that absorb their nutrients from
dead decaying matter.
Parasites derive their nutrients from the body fluids of
living organisms.
Non-biodegradable – term use to describe material that are
inert to decomposition by microorganisms.
Chemoheterotrophs are a very diverse group and shows great
variation in their capcity to metabilize nutrients. Some
organisms are auxotrophs and require the presence of
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specific organic nutrients for their growth. Auxotrophy is
the inability of an organism to synthesize a particular
organic compound required for its growth.
Prototrophs can grow on media that contain only a single organic nutrient for example
glucose from which they synthesize all of their organic molecules.
Bacteriorhodopsin is a protein used by archaea, most
notably halobacteria. It acts as a proton pump, i.e. it
captures light energy and uses it to move protons across
the membrane out of the cell. The resulting proton gradient
is subsequently converted into chemical energy.
Bacteriochlorophylls are photosynthetic pigments that occur
in various phototrophic bacteria. They are related to
chlorophylls, which are the primary pigments in plants,
algae, and cyanobacteria. Groups that contain
bacteriochlorophyll conduct photosynthesis, but do not
produce oxygen.
Q. What is the significance of bacteria having so many
modes of nutrition as well as being able to live with or
without oxygen?
Nitrogen is Essential
Nitrogen is an important component of proteins as well as
nucleic acids. Amino acids and nitrogenous bases are the
building blocks of proteins and nucleic acids respectively,
and are essential nutrients. Bacterial play a key role in
its nitrogen cycling, as well as, other important nutrients
through the ecosystem. The Nitrogen cycle is an example of
a biogeochemical cycle.
Some bacteria can take N2 gas directly from the atmosphere.
Anabaena is a good example of a nitrogen fixing prokaryote. It
belongs to a group called the cyanobacteria.
Still other bacteria like Agrobacteriaum and Rhizobium form
mutualistic relationships with plants and help to trap
atmospheric nitrogen into a more useful form.
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Teachers
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Member of what family of plants form mutualistic symbiotic
relationships in order to fix nitrogen?
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Click here for more on the nitrogen cycle
Which of the following can bacteria use as an energy
source?
a. hydrogen sulfide
b. nitrites
c. sunlight
d. ammonia
e. all of these
What is the role of decomposers in the ecosystem?
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Distinguish saprobes and parasites.
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Why is nitrogen important to living organisms?
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Bacteria play an important role in the cycling of nitrogen.
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http://www.physicalgeography.net/fundamentals/9s.html
Click on the figure for a more detailed description of the
nitrogen cycle.
By what process is nitrogen returned to the atmosphere in
the form of N2?
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By what process is ammonia converted to either nitrate or
nitrate?
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What is the process that takes nitrogen gas (N2) and
assimilates it into organic material?
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What is the source of nitrogenous material that leads to
eutrophication?
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Organisms also are affected by the presence or absence of
oxygen.
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Important oxygen and metabolism terms
Obligate aerobes use O2 for cellular respiration and cannot
grow without it.
Facultative anaerobes will use O2 if it present, but can
also survive by fermentation in its absence.
Obligate anaerobes are poisoned by O2.
Identify three taxa of photoautotrophs
1
2
3
Food for thought
Distinguish between autotrophs and heterotrophs.
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What are the four nutritional modes of bacterial metabolism
and how do they differ?
Summer 2008 Workshop in Biology and Multimedia for High School
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What are decomposers?
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Distinguish between saprobes and parasites?
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Distinguish between auxotrophic mutants and prototrophs.
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What do we call organism that are poisoned by the presence
of atmospheric oxygen?
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Organisms that will use oxygen but can use fermentation in
its absence?
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This protein captures light and moves protons across a
plasma membrane?
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Summer 2008 Workshop in Biology and Multimedia for High School
Teachers
Harvard University Life Sciences – HHMI Outreach Program