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1ESC 590Intro, Microbial Growth & Metabolism
Reading Assignment
Soil Microbiology:An exploratory
ApproachChapters 1 and 2
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1. Soil Microbiology
Soil microbiology is the study of organisms thatlive in the soil.
The main trust of study is on their metabolic and
their roles in energy flow and cycling of nutrientsassociated with primary productivity the energyflow and activities.
The discipline is also concerned with the
environmental impacts, both favorable andunfavorable, of soil microorganisms and the
processes the mediate.
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1. Soil Microbiology
Soil microbiology is concerned with
microbial communities in soil and what
they do. It uses a synecology approachprocess
oriented
Autoecology approach - uses more of anindividual approach.
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2. Soil Biochemistry
Traditionally biochemistry has been defined
as the chemistry that deals with life processes
of plants and animals. The scientific discipline of soil biochemistry
follows this tradition. Many of the reactions
the soil biochemist investigates result fromthe activities of living tissues, e.g.
microorganisms and plants.
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2. Soil Biochemistry
In addition, the study of soil organic matter
its origin and biochemical reactivities, are
also included in the domain of soilbiochemistry even though these may no
longer be in association with any living
system.
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2. Soil Biochemistry
In 1946 J.H. Quastel proposed that the soil
as a whole can be considered an organ
comparable in some respect to a liver or agland to which may be added various
nutrients, pure or complex degraded plant
materials, rain, air and in which enzymatic
reactions occur.
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2. Soil Biochemistry
The products of these reactions are
important steps in elemental cycles, in the
percolation of iron and aluminum humates,in the formation of soil crumb structure, and
in other processes.
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2. Soil Biochemistry
The notion here is that the soil biochemist is
concerned more with what the microbes are
doing in the soil than with precisely whatthe microbes are with respect to size and
shape or the ingredients of taxonomic
schemes.
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2. Soil Biochemistry
In this course we will study soil
biochemistry using this concept which
views the soil as a tissue, containing manykinds of compounds, to which biochemical
principles can be applied.
Soil Cell Membrane
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3. Overview of Metabolism
Metabolism refers to all the chemical
processes that take place within a cell.
It is composed of two basic reactions:- A. Anabolism
- B. Catabolism
Anabolic reactions require energy tosynthesize complex molecules from simpler
ones.
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3. Overview of Metabolism
Catabolic reactions release energy by
braking complex molecules.
All catabolic reactions involve electrontransfer, which allows energy to be captured
in high energy bonds
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4. Microbial Nutrition
Nutrients
- Chemical tools needed to make monomers.
Essential Nutrients- C H,O, P,K,N, S, Ca, Fe, Mg,
Macronutrients
- Needed in large amounts
- Include C, H, O, P, S, K, Mg, Na, Ca, Fe
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4. Microbial Nutrition
Micronutrients (Trace Elements)
- Required in small amounts
- Mainly metals and play role in enzymes- Include Cr, Co, Mn, Mo, Ni, Se, W, V, Zn, Fe
Growth Factors
- Organic compounds required in very smallamounts and only by some cells.
- Include vitamins, amino acids, and nucleotides .
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Culture Media
Culture media are nutrients solutions used
to grow microorganisms.
Two broad classes- A. Chemically defined-prepared by adding
precise amounts of highly purified inorganic or
organic chemicals and distilled water.
- B. Undefined (complex)-These are made up of
digest of casein, beef, soybean, yeast cells other
highly nutritious substances.
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5. Energy Classes of Microorganisms
One of the fundamental properties of living
organisms is their requirement of energy.
Phototrophs, meet their energy requirements
by absorption of a quanta of solar radiation.
Chemotrophs obtain energy needs by
oxidation of preformed organic molecules.
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Characterization of Metabolic
Reactions Based on Electron
Donors/Acceptors
Class Electron Donor Electron AcceptorPhotoautotrophic
(Photolithotroph) H2O, H
2S, H
2R CO
2
Respiration
(organothrops) Organic Compounds O2
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Biological Oxidations
Biological oxidations reactions are
frequently dehydrogenation reactions.
Biological oxidation reactions almostalways involve two electron transfers.
In chemotrophic energy metabolism the
ultimate energy acceptor of electrons isfrequently oxygen.
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The electrons are generally passed to the
final electron acceptor through intermediate
electrons acceptors In most biological oxidations, the
immediate electron acceptor is one of
several coenzymes-specialized moleculesthat function specifically as carriers of
electrons.
Biological Oxidations
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Biological Oxidations
The most common coenzymes are NAD+,
NADP+ and FAD
Aerobic energy metabolism involvesstepwise process collectively called
respiration.
Under anaerobic conditions, oxygen is not
available as electron acceptor, and the
electrons are passed instead to some organic
or inorganic molecule .
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Biological Oxidations
All anaerobic processes are called
fermentations and they are usually further
identified in terms of the principal end
product i.e. the reduced form of the organic or
inorganic electron acceptor.
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6. Oxygen Requirements
Organisms with an absolute requirement for
oxygen arestrict or obligate aerobes.
- Most higher animals are in this category. Strict or Obligate anaerobes cannot tolerate
the presence of oxygen.
- Some bacteria , including soil Clostridia andthose responsible for denitrification are found
in this category
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6. Oxygen Requirements
Facultative organisms are those which can
exist anaerobically, extracting energy from
glucose (or other organic substrates) byfermentative processes, but which can also
function in the presence of oxygen, in
which case they carry out the fullrespiratory sequence.
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7. Methods of Metabolism
All classes of energy yielding reactions can
be classed under four main groups:
1. Respiration2. Fermentative reactions
3. Chemoautotrophic reactions.
4. Photosynthetic
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7.1a Aerobic Respiration
Aerobic Respiration is properly defined as
the oxidation of organic molecules with
molecular oxygen serving as the ultimateelectron acceptor.
The result of aerobic respiration is the
complete degradation of organic molecules
to the products, CO2 and H2O.
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7.1b Anaerobic Respiration
Anaerobic Respiration is a variation of
respiration in which electron acceptors other
than oxygen are used. Electron acceptors used include NO3
-, Fe3+ ,
SO4-, CO3
-
Under anaerobic respiration, less energy isreleased compared to aerobic respiration.
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7.1 Aerobic vs. Anaerobic
Respiration
Class Electron Donor Electron Acceptor
AerobicRespiration Organic Compounds O2
Anaerobic Respiration Organic Compounds Inorganiccompound
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7.2 Fermentation Reactions
In fermentation reactions, organic molecules
are oxidized with the electrons being given to
electron acceptors other than O2.
One common fact concerning each of the
classes of fermentation is that the source of
electrons involved is organic compounds.
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Comparision of Fermentation, Aerobic
Respiration, and Anaerobic Respiration.
Energy-Producing Process Growth Conditions
Fermentation Aerobic or anaerobic
Aerobic respiration Aerobic
Anaerobic respiration Anaerobic
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7.2 Fermentation Reactions
The distinguishing feature of the
fermentative reactions, however is the
nature of the electron acceptors and the
products formed.
The yield of energy obtained from a
fermentative reaction is much less
compared to that of respiration contained in
a given substance.
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7.2. Fermentation Reactions
Class Electron Donor Electron Acceptor
Heterofermentative Organic Compounds Same molecule or
fragment of it.
Multifermentative Organic Compounds Different organic
compound or CO
2
Isofermentative Organic Compounds Another molecule
of substrate
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Comparison of Fermentation,
Aerobic and Anaerobic Respiration.
Energy-
Producing
Process
Growth
Conditions
Final Electron
Acceptor
Type of
Phosphorylation
used to build ATP
Molecules
of ATP
Produced
Fermentation Aerobic oranaerobic
An organic molecule Substrate-level 2
Aerobic
respiration
Aerobic Free oxygen (O2) Substrate-level and
oxidative
38
Anaerobic
respiration
Anaerobic Usually an inorganic
substance (such as
NO3-, SO42-, CO3
2- ),
but not free oxygen
(O2).
Oxidative Variable
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7.3. Chemolithotrophic Metabolism
In this mode of energy generation,
organisms use inorganic chemicals as
electron donors. It usually involves aerobic respiratory
processes but uses an inorganic energy
source rather than an organic one. Examples inorganic electron donors include
H2S, H2, Fe2+ and NH3.
Class Electron Donor Electron Acceptor Products
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Photoautotrophic
(Photolitotroph)
H2O, H2S, H2R CO2 (HCHO)x and other reduced
compounds
Respiration
(Heterotrophs)
Organic Compounds O2 CO2 + H2O
Homofermentative Organic Compounds Same molecule or fragment
of it
Single organic species + CO2 in some
cases
Heterofermentative Organic Compounds Same molecule or fragment
of it.
Mixture of organic compounds
Multifermentative Organic Compounds Different organic
compound or CO2
Organic compounds
Isofermentative Organic Compounds Another molecule of
substrate
Reduced organic compound and
Oxidized organic compound
Anerobic Respiration Organic Compounds Inorganic compound Organic Compound or CO2 + H2O:
more reduced inorganic compound
Chemoautotrophic
(Chemolitotroph)
Inorganic Compounds O2 or another inorganic
compound
Oxidized inorganic compound
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7.4 Photosynthetic Reactions
Photosynthesis may be defined as a series of
reactions which utilize solar energy to
convert CO2 into cellular components. It isimportant both to the carbon and oxygen
cycle.
It is also the chemical source of oxygenwhich is absolutely required by aerobic
organisms.
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