Mic 428 Lecture

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Mic 428 - Lecture 7 Fermentations
Outline
Importance of fermentation. Example of fermented
products. Definitions and discrepancies. Simplific
ations and generalizations. Microorganisms that
do not behave in the typical way. High-energy
compounds and substrate-level phosphorylation. The
relationship of Oxygen to growth and
fermentation.
DIVERSITY!!!
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Fermentations
Fermentation is a subject that has long been of
interest to humankind.

• Cheese
• Bread
• Beer
• Wine

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• Cheese

• Bread
• Beer
• Wine

Around 4000 years ago people have started to
breed animals and process their milk. That's when
the cheese was born.
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• Cheese

• Bread

• Beer
• Wine

Bread has been one of the principal forms of food
for man from earliest times. Loaves and rolls
have been found in ancient Egyptian tombs. In the
British Museum's Egyptian galleries you can see
actual loaves which were made and baked over
5,000 years ago.
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• Cheese
• Bread

• Beer

• Wine

The oldest proven records of brewing are about
6,000 years old and refer to the Sumerians. 
Sumeria lay between the Tigris and Euphrates
rivers including Southern Mesopotamia and the
ancient cities of Babylon and Ur. 
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• Cheese
• Bread
• Beer

• Wine

Wine has been used for at least 4,500 years. The
first wines seem to have originated in the Middle
East. The Romans had carried wine making into
much of Western Europe, especially the Moselle
and Rhine valley sections of France and Germany
and the Danube River valley of Austria.
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Fermentations
The word fermentation implies different things
to different people.
To some, it means any degradative process
mediated by bacteria.
To others, fermentation implies any anaerobic,
microbially-mediated degradative process.
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Fermentations
We will accept the definition of the Brocks
textbook.
Internally balanced oxidation-reduction in which
C from the same external organic compound is
partially reduced and partially oxidized.
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Fermentations
We will accept the definition of the textbook
but we will take into account that some of the
things we learned in MIC 201 were simplifications
that do not apply to every microorganism.
Please, if you dont remember the following basic
concepts from MIC 201, take a look at them again.
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Mechanisms for energy conservation fermentation
and respiration.
Similarities and differences between fermentation
and respiration
Differences involving redox reactions.
Fermentation the redox process occurs in the
absence of usable terminal electron
acceptors. Respiration molecular oxygen (or some
other electron acceptor) is present as a terminal
electron acceptor.
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Differences involving mechanisms of ATP synthesis.
Fermentation ATP produced by substrate-level
phosphorylation. Respiration oxidative
phosphorylation.
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Overall process of fermentation
In a typical fermentation, most of the carbon is
excreted as a partially reduced end product of
energy metabolism and only a small amount is used
in biosynthesis.
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These three previous slides are generalizations
of the process of fermentation!
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Many fermentations involve an anoxic environment,
so decomposition of organic materials occurs
anaerobically.

• There are two problems an organism faces if it is
  to catabolize organic compounds in
  energy-yielding metabolism
• Conserving some of the energy released as ATP.
• Disposing of electrons removed from the electron
  donor.

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• Two problems
• Conserve some of the energy released as ATP.
• Disposing of electrons removed from the electron
  donor.

In fermentation, ATP synthesis generally occurs
by substrate-level phosphorylation, a mechanism
by which high energy phosphate bonds from organic
intermediates of fermentation are transferred to
ADP.
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• There are two problems
• Conserving some of the energy released as ATP.
• Disposing of electrons removed from the electron
  donor.

The second problem is solved by production and
excretion by the organism of fermentation
products generated from the original substrate.
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High energy compounds and substrate-level
phosphorylation.
Key step
Generally organic compounds containing a
phosphate group or a coenzyme-A molecule, the
hydrolysis of which is highly exergonic.
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As most of the high energy compounds can couple
directly to ATP synthesis (- 31.8 kJ/mol), if an
organism can form one or another of these
compounds during fermentation, it can make ATP as
well.
In the following slide you will see pathways for
the anaerobic breakdown of various fermentable
substance to high energy intermediates.
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Major routes of the anaerobic breakdown of
various fermentable substances
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Fermentation end and product formation
Irrespective of their means of forming energy,
fermentative organisms, taken collectively,
produce a wide variety of fermentation end
products. Most of these products arise from
pyruvate metabolism. Some microbes produce many
products, and others produce only a single
product, but fermentation end product formation
is a means of reducing power disposal.
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Energy yields of fermentative organisms
How much ATP can be produced by a fermentative
organism?
2-3 ATP/glucose for glucose fermenters.
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The relationship of Oxygen to growth and
fermentation
Aerobic organisms. Anaerobic organisms. Facultativ
e anaerobic organisms.
For a long time it was believed that a
correlation existed between the ability of an
organism to grow in the presence or absence of
oxygen and the nature of its energy generation
mechanisms.
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The relationship of Oxygen to growth and
fermentation
It was believed that aerobic organisms produced
energy by oxidative phosphorylation via electron
transport and that fermentative organisms were
those that required the absence of oxygen to grow
and produced energy solely by substrate-level
phosphorylation.
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The relationship of Oxygen to growth and
fermentation
Certain organisms are facultative in the sense
that they grow either with or without oxygen, but
they produce energy by substrate-level
phosphorylation under either condition.
Ex. Streptococcus pyogenes.
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The relationship of Oxygen to growth and
fermentation
A different case Saccharomyces cerevisiae.
In the presence of oxygen, S. cerevisiae produces
energy both from substrate-level phosphorylation
and by electron transport with oxygen as the
electron acceptor. Under aerobic conditions, the
organism produces water and carbon dioxide as
major end products of glucose catabolism.
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The relationship of Oxygen to growth and
fermentation
A different case Vibrio succinogenes
Vibrio succinogenes grows under anaerobic
conditions and produces energy by both
substrate-level phosphorylation and by electron
transport.
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The existence of this type of organisms
complicates our understanding of fermentation.
Fermentative organisms cannot be regarded as
those that obtain energy by substrate-level
processes only, because some of them obtain
energy by electron transport as well.
Fermentation diversity
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We can still consider that fermentative organisms
are those that dispose of reducing power by the
reduction or organic compounds regardless or the
nature of their energy generation.