Microbial metablism

Catabolism, anabolism

Fermentation

Respiration

Nitrogen fixtation

The synthesis of peptiglydogen

An overview of metabolism

• Metabolism may be divided into two major parts: catabolism and anabolism.

• Catabolism: larger and more complex molecules are broken down into smaller, simpler molecules with the release of energy.

• Anabolism: the synthesis of complex molecules from simpler ones with the input of energy.

The three

stages of

catabolism

• Carbohydrates and other nutrients serve two functions in the metabolism of heterotrophic microorganisms:

1. They are oxidized to release energy2. They supply carbon or building blocks for the

synthesis of new cell constituents.• Amphibolic pathways: function both

catabolically and anabolically

• Much of the ATP derived from the TCA cycle comes from the oxidation of NADH and FADH2 by the electron transport chain.

SUGAR CATABOLISM

• Glycolysis (Embden, Meyerhof Parnas Glycolysis (Embden, Meyerhof Parnas Pathway)Pathway)

– most bacteriamost bacteria– also animals and plantsalso animals and plants

Other pathways for catabolizing sugars

• Pentose phosphate pathway (hexose Pentose phosphate pathway (hexose monophosphate shunt)monophosphate shunt)– generates NADPHgenerates NADPH– common in plants and animalscommon in plants and animals

• Entner Doudoroff Pathway Entner Doudoroff Pathway – a few bacterial speciesa few bacterial species

GlycolysisGlycolysis

NADNAD NADHNADH

GlucoseGlucose PyruvatePyruvateC6C6 C3C3

ADP ADP ATPATP

FermentationFermentation

2. 2. PyruvatePyruvate

((C3)C3)

1. 1. NADHNADH NADNAD

Short chain alcoholsShort chain alcohols, , fatty acidsfatty acids((C2-C4)C2-C4)

The energy substrate is oxidized and degraded without the participation of an exogenous or extrenally derived electron acceptor. Usually an intermediate such as pyruvate acts the electron acceptor. Anaerobic conditions

Two unifying themes should be kept in mind when microbial fermentation are examined:

Three type fermentation of Saccharomyces cerevisiae

I: pyruvateacetaldehydeethanolII: pH7: glycerolIII: NaHSO3

Lactic acid fermentation

• The reduction of pyruvate to lactate

• Homofermentative（同型发酵的） group: produces only lactic acid as sole product

• Heterofermentative（异型发酵的） group: produces ethanol, CO2 and lactic acid

Respiration

Energy-yielding metablism can make use of exogenous or externally derived electron acceptors.Two different type:

aerobic respiration: the final electron acceptor is oxygen

anaerobic respiration: most often is inorganic such as NO3

-, SO42-, CO2 , Fe3+,

SeO42 -,)

Anaerobic Respiration = Anaerobic Respiration = Glycolysis + FermentationGlycolysis + Fermentation

NADNAD NADHNADH

NADHNADH NADNAD

ATPATP

Krebs Cycle (C4-C6 intermediate compoundsKrebs Cycle (C4-C6 intermediate compounds)

PyruvatePyruvate 33COCO22

((C3)C3)

NADNAD NADHNADH

NADHNADH NADNAD

Oxidative phosphorylationOxidative phosphorylation

OO22 HH22OO

ADPADP ATPATP

((C1)C1)

Aerobic Respiration =Aerobic Respiration =Glycolysis + Glycolysis +

Krebs Cycle/oxidative phosphorylationKrebs Cycle/oxidative phosphorylation

• Pyruvate to COPyruvate to CO22

– NADNAD toto NADHNADH

– glycolysis glycolysis

– Krebs cycleKrebs cycle

• Oxidative phosphorylationOxidative phosphorylation

– NADHNADH to to NAD NAD

– ADPADP to to ATP ATP

Oxidative phosphorylationOxidative phosphorylation

• converts Oconverts O22 to H to H220 0 (oxidative)(oxidative)

• converts ADP to ATP converts ADP to ATP (phosphorylation)(phosphorylation)

• electron transport chainelectron transport chain

• ubiquinones/cytochrome intermediates ubiquinones/cytochrome intermediates

Sugar as sole carbon sourceSugar as sole carbon source

PyruvatePyruvate (C3)(C3)

AcetateAcetate(C2)(C2)

--COCO22

C6C6

Krebs CycleKrebs Cycle

C4C4

PyruvatePyruvate (C3)(C3)

+ + COCO22

FATTY ACIDS AS SOLE CARBON FATTY ACIDS AS SOLE CARBON

SOURCESOURCE

Fatty acidsFatty acids

AcetateAcetate(C2)(C2)

C6C6

Krebs CycleKrebs Cycle

C4C4 C4C4 C2C2++

The glyoxylate cycleThe glyoxylate cycle

.

-

+

C3 C2

C4

C6

C2

C2

C4

C4

C4

C5

C6

Krebs CycleKrebs Cycle

– biosyntheticbiosynthetic

– energy producing energy producing

• Removal of intermediatesRemoval of intermediates

– must be replenished. must be replenished.

• Unique enzymatic replenishment pathwayUnique enzymatic replenishment pathway

– sugars sugars

– fatty acidsfatty acids

Nitrogen fixation

The reduction of atmospheric gaseous nitrogen

to ammonia is callled nitrogen fixation.

Nitrogen fixation occurs in:1. Free-living bacteria.(Azotobacter)2. Bacteria living in symbiotic association with plants such as legumes(Rhizobium)3. cyanobacteria

Nitrogenase

Consistiong of two major protein components: a MoFe protein joined with one or two Fe proteins.1. The MoFe protein contains 2 atoms of molybdenum and 28 to 32 atoms of iron;2. The Fe protein has 4 iron atoms

Mechnisms of anti-oxygen

Nitrogenase is quite sensitive to O2 and must be protected from O2

inactivation within the cell.1.Respiration protection2.Hetercyst formation3.Membrane

Nitrogen reductionN2+8H++8e-+16ATP2NH3+H2+16ADP+16Pi

Root Nodule Bacteria and Symbiosis with legumes

Soybean root nodules Unnodulated soybean

Nodulated soybean

Steps in the formation ofroot nodule in a legumeinfected by Rhizobium

Peptidoglycan synthesis

Staphylococcus aureus

Two carriers participate: uridine diphosphate (UDP) and bactoprenol

BactoprenolBactoprenol is a 55-carbon alcohol that attaches to NAM by a pyrophosphate group and moves peptidoglycan components through the hydrophobic membrane

Eight stages of Peptidoglycan synthesis

1. The formation of UDP-NAM and UDP-NAG2. Amino acids are sequentially added to UDP-

NAM to form the pentapeptide chain.3. The NAM-pentapeptide is transferred from

UDP to a bactoprenol phosphate at the membrane surfacre.

4. UDP-NAG adds NAG to the NAM-pentapeptide to form the peptidoglycan repeat unit.

5. Repeat unit is transported across the membrane to its outer surface by the bactoprenol pyrophosphate carrier.

6. The peptidoglycan unit is attached to the growing end of a peptidoglycan chain to lengthen it by one repeat unit.

7. The bactoprenol carrier returns to the inside of the membrane. A phosphate is released.

8. Peptide cross-links between the peptidoglycan chains are formed by transpeptidation.

Eight stages of Peptidoglycan synthesis

Peptidoglycan synthesis

CytoplasmCytoplasm Cell wallCell wall

undecaprenolundecaprenol

sugarsugar

aminoaminoacidacid

Cell MembraneCell Membrane

Peptidoglycan SynthesisTransport of peptidoglycan precursors across the

cytoplasmic membrane to the growing point of the cell wall

The transpeptidation reaction that lead to the final cross-linking of two peptidoglycan chains

Penicillin inhibits this reaction

Questions

• What are catabolism and anabolism?

• What are Fermentation and Respiration?

• Lactic acid fermentation• aerobic respiration, anaerobic respiration• Nitrogen fixation• Why is Root nodule bacteria and symbiosis so

important for legumes?• Eight stages of Peptidoglycan synthesis