Class Bacterial Nutrition, Growth and Metabolism

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



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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



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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.



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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.


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.



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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



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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



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Oxygen



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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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Thermophilic sulfur bacteria can live and grow in the runoff waters from

such geysers despite the near-boiling temperatures.



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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)



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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



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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.



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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.



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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.



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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.


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Class Bacterial Nutrition, Growth and Metabolism