Bacterial Physiology Metabolism

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Bacterial Physiology -Metabolism Growth

• Pin Lin (? ?), Ph.D.
• Departg ment of Microbiology Immunology, NCKU
• ext 5632
• lingpin_at_mail.ncku.edu.tw
• References
• 1. Chapters 4 in Medical Microbiology (Murray,
  P. R. et al 5th edition)
• 2. ?????? (??? ???, 4th edition)

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Outline

• Metabolic Requirements
• Metabolism the Conversion of Energy
• - Glucose Glycolysis (Embden-Meyerhof-
• Parnas pathway)
• TCA cycles
• Pentose phosphate pathway
• - Nucleic acid synthesis
• Bacterial Growth

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Metabolic Requirements

• 1. Bacteria must obtain or synthesize Amino
  acids,
• Carbohydrates, Lipids gt build up the cell.
• 2. Minimum requirements for bacterial growth
• C, N, H2O, Ion energy
• 3. Growth requirements metabolic by-products
• gt Classify different bacteria
• 4. O2 is essential for animal cells but not for
  all bacteria.
• - Obligate aerobes Mycobacterium
  tuberculosis
• - Obligate anaerobes Clostridium perfringens
• - Facultative anaerobes Most bacteria

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Essential Elements
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Metabolic Requirements-I
Carbon source - Autotrophs (lithotrophs) use
CO2 as the C source Photosynthetic autotrophs
use light energy Chemolithotrophs use
inorganics - Heterotrophs (organotrophs) use
organic carbon (eg. glucose) for growth. -
Clinical Labs classify bacteria by the carbon
sources (e.g. Lactose) the end products
(e.g. Ethanol,). Nitrogen source Ammonium
(NH4) is used as the sole N source by most
microorganisms. Ammonium could be produced from
N2 by nitrogen fixation, or from reduction of
nitrate (NO3-)and nitrite (NO2).
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Metabolic Requirements-II
Sulfur source A component of several coenzymes
and amino acids. Most microorganisms can use
sulfate (SO42-) as the S source. Phosphorus
source - A component of ATP, nucleic acids,
coenzymes, phospholipids, teichoic acid, capsular
polysaccharides also is required for signal
transduction. - Phosphate (PO43-) is usually
used as the P source.
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• Mineral source
• - Required for enzyme function.
• For most microorganisms, it is necessary to
  provide sources
• of K, Mg2, Ca2, Fe2, Na and Cl-.
• Many other minerals (eg., Mn2, Mo2, Co2, Cu2
  and Zn2)
• can be provided in tap water or as contaminants
  of other
• medium ingredients.
• Uptake of Fe is facilitated by production of
  siderophores
• (Iron-chelating compound, e.g. Enterobactin).
• Growth factors organic compounds (e.g., amino
  acids, sugars, nucleotides) a cell must contain
  in order to grow but which it is unable to
  synthesize.

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Environmental factors
pH value Neutrophiles ( pH 6-8) Acidophiles
( pH 1-5) Alkalophiles ( pH 9-11) Internal
pH is regulated by various proton transport
systems in the cytoplasmic membrane. Temperature
Psychrophiles (lt15 or 15-20 oC) Mesophiles (
30-37 oC) Thermophiles ( at 50-60
oC) Heat-shock response is induced to stabilize
the heat-sensitive proteins of the cell.
Aeration Obligate aerobes Facultative
anaerobes Microaerophilics Obligate
anaerobes (Capnophilics bacteria that do not
produce enough CO2 and, therefore, require
additional CO2 for growth.)
Ionic strength and osmotic pressure Halophilic
(Greek for "salt-loving)
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Toxicity of O2 for Anaerobes

• O2 reduced to H2O2 by enzymes.
• 2. O2 reduced to O2- by ferrous ion.
• 3. In aerobes and aerotolerant anaerobes, O2- is
  removed by Superoxide dismutase, while H2O2 is
  removed by Catalase.
• 4. Strict anaerobes lack both Catalase and
  Superoxide dismutase.

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Anaerobic cultivation methods
Excluding oxygen Reducing agents Anaerobic
jar Anaerobic glove chamber
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Outline

• Metabolic Requirements
• Metabolism the Conversion of Energy
• - Glucose Glycolysis (Embden-Meyerhof-
• Parnas pathway)
• TCA cycles
• Pentose phosphate pathway
• - Nucleic acid synthesis
• Bacterial Growth

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Microbial metabolism
1. All cells require the energy supply to
survive. The common energy form gt ATP
(Adenosine Tri-Phosphate) 2. Catabolism
(Dissimilation) - Pathways that breakdown organic
substrates (carbohydrates, lipids,
proteins) to yield metabolic energy for growth
and maintenance. 3. Anabolism (Assimilation) -
Assimilatory pathways for the formation of key
intermediates and then to end products (cellular
components). 4. Intermediary
metabolism-Integrate two processes
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Catabolism
Substrate-level phosphorylation
Fermentation
Glycolysis (EMP pathway)
Aerobic respiration
Pyruvate universal intermediate
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Metabolism of Glucose
1. Here we focus on discussing the metabolism of
glucose. For the metabolism of other organic
compounds (e.g. Proteins or lipids), please
refer to a textbook of Biochemistry. 2.
Bacteria can produce energy from glucose by
fermentation (w/o O2), anaerobic reaction
(w/o O2), or aerobic respiration. 3. Three
major metabolic pathways are used by bacteria to
catabolize glucose (1) Glycolysis (EMP
pathway), (2) TCA cycle, (3) Pentose
phosphate pathway.
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Glycolysis (Embden-Meyerhof-Parnas pathway)
1. The most common pathway for bacteria in
the catabolism of glucose. 2. Reactions
occur under both aerobic and anaerobic
conditions 3. One Glucose gt 2 ATP
(2X2-22) 2 NADH 2 Pyruvate
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Sources of metabolic energy
Respiration chemical reduction of an electron
acceptor through a specific series of electron
carriers in the membrane. The electron acceptor
is commonly O2, but CO2, SO42-, and NO3- are
employed by some microorganisms. Photosynthesis
similar to respiration except that the reductant
and oxidant are created by light energy.
Respiration can provide photosynthetic organisms
with energy in the absence of light.
Substrate-level phosphorylation
Fermentation metabolic process in which the
final electron acceptor is an organic compound.
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Fermentation

• 1. In fermentation, Pyruvate produced from
  glycolysis
• is converted to various end products via
  bacterial
• species.
• 2. The NADH produced during glycolysis is
  recycled to NAD.
• 3. Many bacteria are identified on the basis of
  their
• fermentative end products.
• 4. Fermentation of bacteria produces yogurt,
• sauerkraut, flavors to various cheeses and
  wines.
• 5. Alcoholic fermentation is uncommon in bacteria.

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Function of TCA cycle
1. Via the TCA cycle, Pyruvate from glycolysis or
other catabolic pathways can be completely
oxidized (w/ O2) to H2O CO2 2. Generation of
ATP 3. Supplies key intermediates for amino
acids, lipids, purines, and pyrimidines 4. The
final pathway for the complete oxidation of amino
acids, fatty acids, and carbohydrates.
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Tricarboxylic Acid (TCA) cycle
1. Pyruvate gt Acetyl-CoA 1x NADH gt 3ATP 2.
TCA cycle 3x NADH gt 3x 3 ATP 1x FADH2
gt 1x 2 ATP 1x GTP gt 1x ATP 3. NADH
FADH2 go to the Electron transport chain
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Electron transport chain

• 1. Electrons carried by NADH (FADH2)
• A series of donor-acceptor pairs
• Oxygen terminal electron acceptor
• Aerobic respiration
• 2. Some bacteria use other compounds
• (CO2, NO3-) as terminal acceptor
• Anaerobic respiration
• Produce less ATP

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Aerobic Glucose Metabolism
x2
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Pentose phosphate pathway (hexose monophosphate
shunt)
Nucleotide synthesis

• Functions
• Provides various sugars as precursors of
  biosynthesis, and NADPH for use in biosynthesis
• The various sugars may be shunted back to the
  glycolytic pathway.

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Nucleic acid synthesis
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Nucleic acid synthesis

• 1. Ribose-5-P (product of HMP) synthesis
  of purine ring from sugar moiety inosine
  monophosphate purine monophosphate
  
• Pyrimidine orotate orotidine
  monophosphate (pyrimidine orotate attaches to
  ribose phosphate) cytidine or urine
  (pyrimidine) monophosphate
• Reduction of ribonucleotides at the 2 carbon of
  the sugar portion deoxynucleotides
  

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Bacterial Cell Division

• 1. Replication of chromosome
• 2. Cell wall extension
• 3. Septum formation
• 4. Membrane attachment of
• DNA pulls into a new cell.

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Bacterial growth curve
Lag phase (adaptation) Exponential phase (Log
phase) Determination of the generation time
(doubling time) The ending of this phase is
due to exhaustion of nutrients in the medium and
accumulation of toxic metabolic
products. Stationary phase A balance between
slow loss of cells through death and formation of
new cells through growth. Alarmones is
induced. Some bacteria undergo
sporulation. Decline phase (the death phase)
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Cultivation methods
For microbiologic examination Use as many
different media and conditions of incubation as
is practicable. Solid media are preferred avoid
crowding of colonies. For isolation of a
particular organism Enrichment
culture Differential medium Selective
medium Isolation of microorganisms in pure
culture Pour plate method Streak method For
growing bacterial cells Provide nutrients and
conditions reproducing the organism's natural
environment.
Medium Basic media Rich media
Enrichment media Selective media
Differential media Agar an acidic polysaccharide
extracted from red algae
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Growth, survival and death of microorganisms
Most bacteria reproduce by binary
fission. Measurement of microbial
concentrations Cell concentration (no. of
cells/unit vol. of culture) Viable cell
count Turbidimetric measurements Biomass
concentration (dry wt. of cells/unit vol. of
culture) can be estimated by measuring the
amount of protein or the volume occupied by
cells.
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Bacterial growth in nature
Interaction of mixed communities A natural
environment may be similar to a continuous
culture. Bacteria grow in close association with
other kinds of organisms. The conditions in
bacterial close association are very difficult to
reproduce in the laboratory. This is part of the
reason why so few environmental bacteria have
been isolated in pure culture.
Biofilms Polysaccharide encased community of
bacteria attached to a surface. Attachment of
bacteria to a surface or to each other is
mediated by glycocalyx. About 65 of human
bacterial infection involve biofilms. Biofilms
also causes problems in industry. Bioremediation
is enhanced by biofilms.
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Biofilm a community of microbes embedded in an
organic polymeric matrix (glycocalyx, slime),
adhering to an inert or living surface.
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The End
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