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UNIT 2: BACTERIAL
METABOLISM AND
FERMENTATION
Fermentation and Pasteurization
• Pasteur showed that microbes are responsible for
fermentation
• Fermentation is the conversion of sugar to
alcohol or acid
• Fermentation is used to make cheese, yogurt,
beer and wine
• Microbial growth is also responsible for spoilage
of food
• Bacteria that use alcohol and produce acetic acid
spoil wine by turning it to vinegar (acetic acid) and
bacteria that utilize lactose to produce lactic acid
transform milk into yogurt
Fermentation and Pasteurization
• Pasteur demonstrated that
these spoilage bacteria could
be killed by heat that was not
hot enough to evaporate the
alcohol in wine
• Pasteurization is the
application of a high heat for
a short time
Figure 1.4
A Nutritional Classification of
Organisms
Figure 5.28
A Nutritional Classification of
Organisms
Figure 5.28
A Nutritional Classification of
Organisms
Figure 5.28
Metabolic Diversity among Organisms
Nutritional Type
Energy Source
Carbon Source
Example
Photoautotroph
Light
CO2
Oxygenic: Cyanobacteria
plants
Anoxygenic: Green,
purple bacteria
Photoheterotroph
Light
Organic
compounds
Green, purple nonsulfur
bacteria
Chemoautotroph
Chemical
CO2
Iron-oxidizing bacteria
Chemoheterotroph
Chemical
Organic
compounds
Fermentative bacteria
Animals, protozoa,
fungi, bacteria.
Carbohydrate Catabolism
• The breakdown of carbohydrates to
release energy
• Glycolysis
• Krebs cycle
• Electron transport chain
A Summary of Respiration
• Aerobic respiration: The final electron acceptor
in the electron transport chain is molecular
oxygen (O2).
• Anaerobic respiration: The final electron
acceptor in the electron transport chain is not O2
(rather an inorgainc molecules containing sulfate,
nitrate, nitrite, carbonate, etc..).
• Yields less energy than aerobic respiration because only part of the
Krebs cycles operates under anaerobic conditions.
Glycolysis
• The oxidation of glucose to pyruvic acid
produces ATP and NADH
Preparatory Stage of Glycolysis
• 2 ATP are
invested
• Glucose is
split to form 2
glucose-3
-phosphate
Figure 5.12, steps 1–5
Cellular Respiration
• Oxidation of molecules liberates
electrons for an electron transport chain
• ATP is generated by oxidative
phosphorylation
Energy-Generating Stage
of Glycolysis
• 2 glucose-3-
phosphate oxidized
to 2 pyruvic acid
• 4 ATP produced
• 2 NADH produced
Figure 5.12, steps 6–10
Overall Result of Glycolysis
• Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+
 2 pyruvic acid + 4 ATP + 2 NADH + 2H+
Intermediate Step
• Pyruvic acid (from glycolysis) is
oxidized and decarboyxlated
Figure 5.13
Acetyl CoA
The
Krebs
Cycle
Carbohydrate Catabolism
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial matrix
Cytoplasm
ETC
Mitochondrial inner membrane Plasma membrane
The Electron Transport Chain
• A series of carrier molecules that are, in turn,
oxidized and reduced as electrons are passed
down the chain
• Energy released can be used to produce ATP
by chemiosmosis
Chemiosmotic Generation of ATP
Figure 5.16
An Overview of Chemiosmosis
Figure 5.15
Fermentation
• Any spoilage of food by microorganisms
(general use)
• Any process that produces alcoholic
beverages or acidic dairy products (general
use)
• Any large-scale microbial process occurring
with or without air (common definition used in
industry)
Fermentation
• Scientific definition:
• Releases energy from oxidation of organic
molecules
• Does not require oxygen
• Does not use the Krebs cycle or ETC
• Uses an organic molecule as the final electron
acceptor
Figure 5.11
An Overview of Fermentation
Figure 5.18a
Fermentation
• Alcohol fermentation: Produces ethanol +
CO2
• Lactic acid fermentation: Produces lactic
acid
• Homolactic fermentation: Produces lactic
acid only
• Heterolactic fermentation: Produces lactic
acid and other compounds
Types of
Fermentation
Figure 5.19
End-Products of Fermentation
Figure 5.18b
A Fermentation Test
Figure 5.23
Types of Fermentation
Table 5.4
Types of Fermentation
Table 5.4
Requirements of ATP Production
Figure 5.27