2. Basic Concepts
Definitions
Metabolism:The processes of catabolism and
anabolism
Catabolism:The processes by which a living
organism obtains its energy and raw materials
from nutrients
usually release energy that is used to drive
chemical reactions
Anabolism:The processes by which energy and
raw materials are used to build macromolecules
and cellular structures (biosynthesis)
The energy of catabolic reactions is used to
drive anabolic reactions
7. Bacterial Metabolism
Exoenzymes: Bacteria cannot transport large
polymers into the cell
They must break them down into basic subunits for
transport into the cell
therefore they elaborate extracellular enzymes for
the degradation of;
carbohydrates to sugars (carbohydrases)
proteins to amino acids (proteases)
and lipids to fatty acids (Lipases)
8. – After Sugars are made or obtained, they are the
energy source of life
– Breakdown of sugar(catabolism) different ways:
• Aerobic respiration
• Anaerobic respiration
• Fermentation
Energy Generating Patterns
9. Aerobic respiration
– Most efficient way to extract energy from glucose
– Process: Glycolysis
Krebs Cycle
Electron transport chain
– Glycolysis: Several glycolytic pathways
– The most common one:
glucose-----> pyruvic acid + 2 NADH + 2ATP
10. Glycolytic Pathways
4 major glycolytic pathways found in different
bacteria:
Embden-Meyerhoff-Parnas pathway
“Classic” glycolysis
Found in almost all organisms
Hexose monophosphate pathway
Also found in most organisms
Responsible for synthesis of pentose sugars used in
nucleotide synthesis
Entner-Doudoroff pathway
Found in Pseudomonas and related genera
Phosphoketolase pathway
Found in Bifidobacterium and Leuconostoc
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15. Anaerobic respiration
Final electron acceptor : never be O2
Sulfate reducer: final electron acceptor is sodium
sulfate (Na2 SO4)
Methane reducer: final electron acceptor is CO2
Nitrate reducer : final electron acceptor is sodium
nitrate (NaNO3)
O2/H2O coupling is the most oxidizing, more energy in
aerobic respiration
Therefore, anaerobic is less energy efficient.
16. Fermentation
is a metabolic process process that
converts sugar to acids, gases and/or alcohol
It occurs in yeast and bacteria, but also in oxygen-
starved muscle cells
as in the case of lactic acid fermentation
Fermentation takes place in the lack of oxygen
when the electron transport chain is unusable and
becomes the cell’s primary means of ATP (energy)
production
17. Features of fermentation pathways
Pyruvic acid is reduced to form reduced organic
acids or alcohols
The final electron acceptor is a reduced derivative
of pyruvic acid
NADH is oxidized to form NAD: Essential for
continued operation of the glycolytic pathways
O2 is not required
No additional ATP are made
Gasses (CO2 and/or H2) may be released
19. Examples of fermentation pathways
a) Lactic acid fermentation
• Found in many bacteria; e.g. Streptococcus spp., Lactobacillus
acidophilus
b) Mixed acid fermentation
• e.g. Escherichia coli
• basis of the methyl red test
c) 2,3-Butanediol fermentation
• e.g. Enterobacter aerogenes
• basis of theVoges-Proskauer reaction
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23. Microbial nutrition
Aspect of microbial physiology that deals with supply
of monomers that cells need for growth
Nutrients requirement differ because organisms differ
Macronutrients and Micronutrients
24. Carbon
All cells require carbon
On a dry weight basis typical cell is about 50% carbon
Major element in classes of macromolecules
Bacterial can assimilate different organic carbon
compounds
(Amino acids, sugars, organic acids, etc)
25. Nitrogen
Second abundant element
12% of dry weight
Important in proteins, nucleic acids
In environment N is available in NH3 or NO3
Most bacteria are capable of using NH3 as sole nitrogen
source
Nitrogen gas can be used with certain bacteria (Nitrogen
fixing bacteria)
26. Other Macronutrients
Phosphorus:
organic
inorganic phosphates
Structural role in nucleic acids and phospholipids
Sulfur:
Cysteine
Methionine
Sulfur is from inorganic sources either sulfate and
sulfide
Potassium, Magnesium, Calcium
