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8/6/2019 Class Bacterial Nutrition, Growth and Metabolism
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Bacterial Nutrition,
Growth and
Metabolism
Dr. Halide L. Abella
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Energy Metabolism
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Overview
y Metabolism
The sum of all chemical processes carried out by living organisms
It includes: anabolism and catabolism
y Anabolism
Reactions that require energy to synthesize complex molecules
from simpler ones
Needed for growth, reproduction and repair of cellular structures.
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Overview
y
Catabolism Reactions that release energy by breaking complex molecules into
simpler one
Provides an organism with energy for its life processes, including
movement, transport and the synthesis of complex molecules
(anabolism) All catabolic reactions involve electron transfer
Allows energy to be captured in high-energy bonds in ATP and other
similar molecules.
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Overview
y Oxidation
Loss or removal of electrons
When a substance losses electrons, it is oxidized and energy is released.
Many substances combine with oxygenx Transfer their electrons to oxygen
x Oxygen need not be present if another electron acceptor is available
y Reduction
Gain of electrons When a substance gains electrons, it is reduced
y Oxidation and reduction must occur simultaneously.
The reactions are sometimes called redox reactions.
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Energy and Work
Energy
The capacity to do work or to cause particular changes.
All physical and chemical processes are the result of the application or
movement of energy.
Three major types of work carried out by living cells
Chemical work
Transport work
Mechanical work
Chemical Work
y Involves the synthesis of complex biological molecules required by cells
from much simpler precursors.
y Energy is needed to increase the molecular complexity of a cell.
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Transport Work
Transport of molecules and ions across cell membranes against an electro-
chemical gradient
Requires energy input
Function:
Take up nutrients
Eliminate wastes
Maintain ion balancesMechanical Work
y Occurs when there changes in the physical location of organisms, cells, andstructures within cells.
y Requires energy input.
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ATP
Adenosine triphosphate
Energy currency of the cell
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ATP
When ATP breaks down to ADP, energy is made available for useful work
Energy from photosynthesis, aerobic respiration, anaerobic respiration,and fermentation is used to resynthesize ATP from ADP and Pi.
An energy cycle is created in the cell
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Classificiation of All Microorganisms
AccordingT
oE
nergy and Carbon Source
All microorganisms
Autotrophs/LithotrophsPhoto-autotrophsChemo-autotrophsHeterotrophs/OrganotrophsPhoto-heterotrophsChemo-heterotrophs
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Autotrophic/Lithotrophic Bacteria
Utilize carbon dioxide as sole source of carbon
Synthesize from the CO2 all the carbon skeletons of all their organic
metabolites
Require only water, inorganic salts, and CO2 for growth.
Energy is derived either from light or from oxidation of one or moreinorganic substances
y Unable to utilize CO2 as the sole source of carbon
y Require carbon in an organic form such as glucose
y Energy is derived either from light or from a portion of the organic
compound
y All of the bacteria that cause disease in humans.
Heterotrophic/Organotrophic Bacteria
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Type Carbon
Source
Energy Source Electron
Donor
Examples
Photo-
lithotrophs
CO2 Light Inorganic
compounds(H2S, S)
=Photosynthetic
bacteria-green sullfur
-purple sulfur
-cyanobacteria
=Algae
Photo-
organotrophs
Organic
compounds
Light Organic
compounds
=Purple nonsulfur
and
=Green nonsulfur
bacteria
Chemo-
lithotrophs
CO2 Oxidation-
reduction
reactions of
inorganic
compounds
Inorganic
compounds
(H2, S, H2S,
Fe, NH3)
=Iron, Sulfur,
Hydrogen and
Nitrifying bacteria
=Some
Archaeobacteria
Chemo- Organic Oxidation-
Organic =Pathogenic bacteria
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Scheme Pathways
Involved
Final Electron
Acceptor
Products Chief Microbe
Type
Aerobic
Respiration
Glycolysis, TCA
cycle, electron
transport
O2 ATP, CO2, H2O Aerobes
Facultativeanaerobes
Anaerobic Metabolism
Fermentation Glycolysis Organic
molecules
ATP, CO2,
ethanol, lactic
acid
Facultative,
aerotolerant,
strict anaerobes
Anaerobic
Respiration
Glycolysis, TCA
cycle,electron
transport
Various
inorganic
salts(NO3-,
SO4-2, CO3-2)
CO2, ATP,
organic
acids,H2S, CH4,
N2
Anaerobes;
some
facultatives
Metabolic Processes
Among Heterotrophic Organisms
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Aerobic Respiration
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Glycolysis
Also called the Embden-Meyerhof-Parnas (EMP) pathway
It does not require oxygen but can occur in either the presence of absence
of oxygen
Enzymatically converts glucose through several steps into pyruvic acid
A central metabolite
Occupies an important position in several pathways
Alternatives to Glycolysis
Other metabolic pathways utilized by microorganisms for glucose oxidation
Pentose Phosphate Pathway
Entner-Doudoroff Pathway
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Pentose Phosphate Pathway
y Phosphogluconate Pathway
y Utilized by Brucella abortus, species of Acetobacter, Escherichia coli
and Bacillus subtilis
y Can function at the same time as glycolysis
y It breaks down not only glucose but also five- carbon sugars
(pentoses).
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Entner-Dourodoff Pathway
Carried out by Pseudomonas,
Azobacter and Neisseria
Replaces the glycolytic and
pentose phosphate pathways
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Fate of Pyruvic Acid (Pyruvate)
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Fermentation
Incomplete oxidation of glucose or other carbohydrates in the absence
of oxygen
Uses organic compounds as the terminal electron acceptors
Yields a small amount of ATP.
Defined by bacteriologists as the formation of acid, gas, and other
products by the action ofvarious bacteria on pyruvic acid.
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Fermentation and Biochemical Testing
Knowledge of fermentation products
Important in industrial production
Important in identifying bacteria by
biochemical tests
Specimens are grown in media containing
various carbohydrates, and the production
of acid or acid and gas is noted.
E
xamples
Escherichia ferments the milk sugar,
lactose
Shigella and Proteus do not.
Escherichia can be further differentiated
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Anaerobic Respiration
Anaerobic respiratory system
Functions like the aerobic cytochrome system
Except it utilizes oxygen-containing salts, rather than free oxygen, as
the final electron acceptor.
Nitrate (NO3-) and nitrite (NO2-) reduction systems
Seen in E. coli and species of Bacillus and Pseudomonas
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Energy-Yielding Autotrophic Metabolism
In photoautotrophs
Photosynthesis
In chemoautotrophs
y The capture of energy from light and the use of this energy tomanufacture carbohydrates from carbon dioxide
y Photosynthesis occurs in green and purple bacteria, in cyanobacteria, in
algae, and in higher plants.
y occurs in two parts
the photo part, or the light reactions
x light energy is converted to chemical energy
the synthesis part, or the dark reactions
x chemical energy is used to make organic molecules
Photosynthesis
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Chemoautotrophs
Unable to carry out photosynthesis but can oxidize inorganic
substances for energy
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Genetic Regulation
2. Catabolite repression
Sometimes called glucose effect
Frequently observed when organisms are grown in glucose and some
other rapidly metabolizable energy source.
There is repression of synthesis of enzymes that would metabolize
the added substrate less rapidly than glucose.
Example
E. coligrown in a medium containing both glucose and lactose
It uses glucose preferentially until the sugar is exhausted.
Then after a short lag, growth resumes with lactose as the carbon
source.
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Metabolic Regulation
Adenylate Energy Charge
Adenine nucleotides (ATP, ADP & AMP) are strategically placed to
regulate the entire metabolic economy of the cell
Catabolic sequences contain regulatory enzymes that are either
Activated by ADP or AMP OR
Inhibited by ATP
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Modulation of the Glycolytic Pathway
Pasteur Effect
Pasteurization involves heating food to a temperature that kills disease-
causing microorganisms and substantially reduces the levels of spoilage
organisms.
Less glucose is consumed
The accumulation of lactate is decreased
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Pasteur & The Wine-to-Vinegar Connection
Louis Pasteur was hired by French wine makers to uncover the causes ofperiodic spoilage in wines. Especially troublesome was the conversion of
wine to vinegar and the resultant sour flavor.
After extensively studying beer making and wine grapes, Pasteur concluded
that wine, both fine and not-so-fine, was the result of microbial action on
the juices of the grape and that wine disease was caused bycontaminating organisms that produced undesirable products such as acid.
Although he did not know it at the time, the bacterial contaminants
responsible for the acidity of the spoiled wines were likely to be Acetobacter
or Gluconobacterintroduced by the grapes, air, or winemaking apparatus.
Pasteurs far-reaching solution to the problem is still with us today mild
heating, or pasteurization, of the grape juice to destroy the contaminants,
followed by inoculation of the juice with a pure yeast culture.
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Physiology of Bacterial Growth
Requirements for Growth
Uptake of Nutrients
Bacterial ChemotaxisGrowth of Bacterial Populations
Bacterial Cell Cycle
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Requirements For Growth
Essential Nutrients
Any substance, whether in elemental or molecular form, that must be
provided to an organism
2 categories of essential nutrients
Macronutrients or macroelements
Micronutrients or trace elements
Requirements for Growth
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Macronutrients
Required by the microorganisms in relatively large amount
C H O N S P
are components of carbohydrates, lipids, proteins, and nucleic acids
The remaining macroelements exist in the cell as cations and play a variety
of roles.
Potassium is required for activity by a number of enzymes, including
some of those involved in protein synthesis.
Calcium contributes to the heat resistance of bacterial endospores.
Magnesium serves as a cofactor for many enzymes, complexes with
ATP, and stabilizes ribosomes and cell membranes
Iron (Fe2+ and Fe3+) is a part of cytochromes and a cofactor for
enzymes and electron-carrying proteins.Requirements for Growth
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Micronutrients
Manganese, zinc, cobalt, molybdenum, nickel, and copper (trace elements)
Needed by most cells
Cells require such small amounts that contaminants in water, glassware, and
regular media components often are adequate for growth.
Normally a part of enzymes and cofactors, and they aid in the catalysis ofreactions and maintenance of protein structure.
Zinc
present at the active site of some enzymes
Manganese
aids many enzymes that catalyze the transfer of phosphate groups.
Molybdenum
Requirements for Growth
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Carbon and Carbon Dioxide
The majority of carbon compounds involved in the normal structure andmetabolism of all cells are organic.
Heterotrophs
Organisms that must obtain its carbon in an organic form.
Organic carbon originates from the bodies of other organisms
Heterotrophs are dependent on other life forms
Among the common organic molecules that can satisfy their carbon
requirement are proteins, carbohydrates, lipids, and nucleic acids.
In most cases, these nutrients provide several other elements as well.
Autotrophs Organisms that uses CO2, an inorganic gas, as its carbon source.
Because autotrophs have the special capacity to convert CO2 into
organic compounds, they are not nutritionally dependent on other
living things.
Requirements for Growth
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Carbon and Carbon Dioxide
Some organisms require a higher concentrations (10%) of carbon dioxide
than what is normally present in the atmosphere (0.03%).
Neisseria and Brucella
Capnophiles
Carbon dioxideloving organisms
They thrive under conditions of low oxygen and high carbon dioxideconcentration.
Requirements for Growth
Nitrogen
The main reservoir of nitrogen is nitrogen gas (N2)
It makes up about 79% of the earths atmosphere.
This element is needed in the structure of proteins, DNA, RNA, and ATP.
the primary sources of nitrogen for heterotrophs
to be useful, they must first be degraded into their basic building blocks
(proteins into amino acids; nucleic acids into nucleotides).
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Growth Factors
Many heterotrophic bacteria are unable to grow unless supplied withone or more growth factors
Usually provided in the culture medium in the form of yeast extract or
whole blood
It includes B-complex vitamins, amino acids, purines and pyrimidines
Prototrophic organisms
Organisms that do not require an exogenous source of a given
growth factor
Capable of synthesizing their own
Auxotrophic organisms Require the addition of growth factor to culture media in order for
growth to occur.
Requirements for Growth
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Inorganic Ions Small amounts of inorganic ions are required by all bacteria
Magnesium
Functions to stabilize ribosomes, cell membranes and nucleic
acids
Required for the activity of many enzymes
Potassium
Required for the activity of many enzymes
In gram (+) organisms, its composition in the cell is influenced
by the teichoic acid content of the cell wall
Requirements for Growth
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Oxygen
Classification of bacteria based on their oxygen requirements Obligate anaerobes
Grow only under conditions of high reducing intensity
Oxygen is toxic
Aerotolerant anaerobes
Not killed by exposure to oxygen
Facultative anaerobes
Capable of growth under both aerobic and anaerobic conditions
Obligate aerobes
R
equire oxygen for growth Microaerophilic organisms
Grow best at low oxygen tensions
High oxygen tension is inhibitory
Requirements for Growth
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Oxygen
Requirements for Growth
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Physical Requirements
1. Temperature
There is an optimal temperature at which the organism grows most
rapidly and a range of temperatures over which growth can occur.
Cellular division is specially sensitive to the damaging effects of high
temperatures.
Classification
Psychrophilic
-5 to 30 C, optimum at 10 to 20 C
Mesophilic
10 to 45 C, optimum at 20 to 40 C
Human pathogensRequirements for Growth
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Physical Requirements
Thermophilic sulfur bacteria can live and grow in the runoff waters from
such geysers despite the near-boiling temperatures.
Requirements for Growth
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Physical Requirements
The temperature range over which an organism grows is determined largely
by the temperatures at which its enzymes function. Within thistemperature range, three critical temperatures can be identified:
1. Minimum growth temperature
the lowest temperature at which cells can divide.
2. Maximum growth temperature
the highest temperature at which cells can divide.
3. Optimum growth temperature
the temperature at which cells divide most rapidly (shortest
generation time)
Requirements for Growth
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Physical Requirements
2. Hydrogen Ion Concentration
pH of the culture can affect the growth rate
pH 7.2 to pH 7.6 optimal pH for most pathogenic bacteria
Classification according to their tolerance for acidity and alkalinity
Acidophiles -pH range of 6.5 to 7.0
Neutrophiles -pH range of 7.5 to 8.0
Alkalophiles -pH range of 8.5 to 9.0
Requirements for Growth
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Physical Requirements
Acidophiles
Lactobacillus produces lactic acid but tolerates only mild acidity
Acid drips from long, hanging colonies of bacteria which have the
consistency of strings of mucus.
Requirements for Growth
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Physical Requirements
Neutrophiles
Most of the bacteria that cause human disease are neutrophiles
Alkalophiles
Vibrio cholerae, the causative agent of the disease cholera, grows
best at a pH of about 9.0.
Alcaligenes faecalis, which sometimes infects humans already
weakened by another disease, can create and tolerate alkaline
conditions of pH 9.0 or higher.
Many bacteria often produce sufficient quantities of acids as metabolic
by-products that eventually interfere with their own growth.
To prevent this situation in the laboratory cultivation of bacteria, buffers
are incorporated into growth media to maintain the proper pH levels.
Requirements for Growth
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Physical Requirements
3. Osmotic Conditions
The concentration of osmotically active solutes inside a bacterial cell is
higher than the concentration outside the cell.
Cells in such hyperosmotic environments lose water and undergo
shrinking of the cell.
Cells in distilled water have a higher osmotic pressure than their
environment and, therefore, gain water. Cells fill with water and
become distended.
Majority of bacteria are osmotically tolerant
Except for the Mycoplasmas and other cell wall-defective organisms.
Their cell membranes contain transport systems that regulate the
movement of dissolved substances across the membrane.
Requirements for Growth
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Physical Requirements
Halophiles
Salt-loving organisms
Require moderate to large quantities of salt (sodium chloride).
Their membrane transport systems actively transport sodium
ions out of the cells and concentrate potassium ions inside them.
Typically found in the ocean, where the salt concentration (3.5%)
is optimum for their growth.
Extreme halophiles require salt concentrations of20% to 30%.
They are found in exceptionally salty bodies of water, such as the
Dead Sea, and sometimes even in brine vats, where they cause
spoilage of pickles being made.
Requirements for Growth