This document discusses bacterial metabolism. It begins by defining metabolism as the sum of all chemical reactions occurring in a cell, and notes that bacterial metabolism is essential for bacterial existence, the environment, and produces medically and commercially important products. It then defines catabolic and anabolic reactions, and lists the main components of metabolism like enzymes, ATP, electron carriers, and precursor metabolites. The document goes on to describe various metabolic pathways like glycolysis, the pentose phosphate pathway, the Entner-Doudoroff pathway, cellular respiration, the Krebs cycle, electron transport chains, anaerobic respiration, and fermentation. It discusses the products of fermentation and specific pathways like lactic acid fermentation. Finally, it briefly

1. Santosh Yadav
BACTERIAL METABOLISM
Santosh Yadav
M.Sc. Clinical Microbiology
Dept. of Microbiology
Institute of Medicine
Tribhuvan Univarsity Teaching Hospital, Nepal

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Metabolism
 Sum total of all the chemical reactions occuring
in the cell ( i.e. biosynthetic and degradative)
 Metabolism in bacteria is essential for their
existance , for environment , and products are
commercially and medically important for human
beings.
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CATABOLIC AND ANABOLIC REACTIONS
 Reactions that cause
breakdown of complex
molecules into simpler
form with relase of
energy is catabolic
reactions.
 Energy requiring
reactions that build up
complex organic
molecules from simpler
ones is anabolic
reactions.
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Components of metabolism
COMPONENTS FUNCTIONS
Enzymes Biological catalyst, fascilitates each step of metabolic reaction
by lowering the activation energy of reaction.
Adenosine triphosphate
(ATP)
serves as energy currency of cell ,
Energy source Compund that is oxidised to release energy
, also called an electron donor.
Electron carriers carry the electrons that are removed during the oxidation of
energy source (NAD⁺, NADP⁺ , and FAD ( their reduced form
NADH , NADPH , and FADH₂) .
Precursor metabolites Intermediate metabolite that link anabolic and catabolic
pathways, like pyruvate, acetyl-coA, glucose -6-p, etc.
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Role of ATP
 Is energy currency of cell,
serving as ready and
immediate donor of free
energy.
 Energy is releases when
phosphate bond is broken,
hence it is called high
energy phosphate bond.
 Synthesis and breakdown of
ATP continuously occurs in
cell during degradative and
synthetic process.
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Generation of ATP
Bacteria uses three mechanism of
phosphorylation to generate ATP
from ADP.
1)Substrate level
phosphorylation
C-C-C-P + ADP C-C-C + ATP
In this mechanism , a high energy
phosphate from a phosphorylated
substrate is directly transferred to
to ADP.
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Contd…
2) Oxidative phosphorylation:
ATP generation duting ETC.
3)Photophosphorylation
 Occurs in phototrophs.
 Derive ATP using radiant energy of the sun.
 These ATP are then utilized to synthesize mainly
glucose .
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METABOLIC PATHWAYS OF
ENERGY GENERATION
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GLYCOLYSIS
 Embden-Mayerhof Parnas
pathway.
 Stepwise Conversion of glucose to
pyruvate and each step require
specific enzyme.
 Occurs in cytosol.
 Does not require oxygen and hence
occur in both aerobic and anaerobic
bacteria.
 Three phases :- preparatory phase,
splitting phase and energy generation
phase.
 2 molecules of pyruvic acids are
formed from each glucose .
 Net gain of 2 ATP by substrate
level phosphorylation and
formation of 2 reduced substrate
i.e. NADH(6 ATP).
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Pathways alternative to glycolysis
 Many bacteria have another pathway in addition to
glycolysis for degradation of glucose.
1) Pentose phosphate pathway, and
2) Entner Doudoroff pathway.
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Pentose phosphate pathway
 Hexose monophosphate shunt.
 Occurs simultaneously with
glycolysis and provides
breakdown of both pentose sugar
and glucose.
 Important Feature :- intermediate
pentoses are used for nucleic
acid synthesis, amino acid
synthesis and glucose from CO2
in photosynthetics.
 Important producer of reduced
coenzyme i.e. NADPH , used for
biosynthetic reactions.
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Entner –Doudoroff pathway
 Bacteria having enzyme for
Entner –Doudoroff pathway
can metabolize without glycolysis
or PPP.
 Found in some Gram negative
bacteria like Psedomonas spp,
Rhizobium,etc.. and generally
not found in Gram positive
bacteria.
 Produces 1 molecule NADH, 1
molecule NADPH and 1 molecule
of ATP ( from 1 glucose).
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Cellular respiration and fermentation
 Pyruvate obatained from glucose breakdown are
channeled either to respiration or to fermentation.
RESPIRATION:- is ATP generating process in
which molecules are oxidized and the final
electron acceptor is an inorganic molecules.
TYPES OF RESPIRATION :-
Aerobic respiration:- final electron acceptor is O₂
and occurs in aerobes.
Anaerobic respiration: final electron acceptor is
inorganic molecule other than O₂ .
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Krebs cycle or TCA cycle
 Is second phase of aerobic respiration.
 Cytoplasmic membrane.
 Pyruvate formed enters TCA cycle only after converted
into acetylCoA by decarboxylation rxn ( transition
phase).
 Starts with condensaion of acetylCoA and
oxaloacetate.
 AcetylCoA is oxidized and released as CO2 and
oxaloacetate is regenerated.
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Contd…
 From TCA cycle, oxidation of one acetylCoA
molecule produce 3 NADH , 1 FADH₂ and
1 GTP. ( 1 lucose=2 pyruvate= 2 acetylCoA)
 All the NADH and FADH2 enters into electron
transport chain and finally ATP are generated.
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Electron transport chain
 Last phase of respiration which generates ATP
from reduced substrates.
 Consists of a sequence of carrier molecules though
which electrons passes.
 Occurs in plasma membrane ( eukaryotic cell-
inner mitochondrial membrane).
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Contd…
 Three classes of carrier molecules
1)Flavoprotein :- coenzyme derived from viatmin B2 (riboflavin)
and perform alternating oxidation and reduction reaction.
3)Ubiquinones :- small non protein carriers.
2)Cytochromes :-protein with iron containing group (heme).
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• Electron transport chain is different in different bacteria ,
even a single bacteria have more than one type of ETC but
their target is to derive energy in the form of ATP.
Contd…

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Anaerobic respiration
 Final electron acceptor is NO3⁻ , NO2⁻, N₂O,
SO₄⁻⁻,CO₃⁻⁻, etc. and occurs in strict anaeres and
facultative anaerobes.
 Sometimes Pseudomonas sps and Bacillus sps can
use nitrate as final e⁻ acceptor.
 ATP generation varies from bacteria to bacteria
and always less than aerobic respiration.
 Alternative electron carriers are used in the ETC.
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Contd…..
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Fermentation
 Used by organisms that cannot respire because of
either lack of inorganic electron acceptor or
absence of ETS.
 Terminal electron acceptor is always organic
compound.
 End product depends on type of microrganisms.
 Analysis of end product is valuable in identifying
particular bacteria.
 ATP generating pathway is usually glycolysis(
2ATP).
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Products of fermentation
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Lactic acid fermentation
Homolactic fermenters use the glycolytic
pathway and directly reduce almost all their pyruvate
to lactate with the enzyme lactate dehydrogenase ( eg.
Lactobacillus spp)
Heterolactic fermenters form substantial amounts
of products other than lactate; many produce lactate,
ethanol, and CO2( Escherichia coli).
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Catabolism of other substrates
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Anabolism
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