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 energy 2.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 FADH 2 by the electron transport chain.

SUGAR CATABOLISM Glycolysis (Embden, Meyerhof Parnas Pathway)Glycolysis (Embden, Meyerhof Parnas Pathway) –most bacteria –also animals and plants

Other pathways for catabolizing sugars Pentose phosphate pathway (hexose monophosphate shunt)Pentose phosphate pathway (hexose monophosphate shunt) –generates NADPH –common in plants and animals Entner Doudoroff PathwayEntner Doudoroff Pathway –a few bacterial species

Glycolysis Glycolysis NADNADH Glucose Pyruvate C6C3 ADPATP

Fermentation 2. Pyruvate (C3) 1. NADH NAD Short chain alcohols, fatty acids (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: pyruvate  acetaldehyde  ethanol II: pH7: glycerol III: NaHSO 3

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, CO 2 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 NO 3 -, SO 4 2-, CO 2, Fe 3+, SeO 4 2 -,)

Anaerobic Respiration = Glycolysis + Fermentation NADNADH NADH NAD ATP

Krebs Cycle (C4-C6 intermediate compounds Krebs Cycle (C4-C6 intermediate compounds ) Pyruvate Pyruvate 3CO 2 (C3) NADNADH NADH NAD Oxidative phosphorylation O2 O2O2 O2 H2OH2OH2OH2O ADP ATP (C1)

Aerobic Respiration = Glycolysis + Krebs Cycle/oxidative phosphorylation Pyruvate to CO 2Pyruvate to CO 2 –NAD to NADH –glycolysis –Krebs cycle Oxidative phosphorylationOxidative phosphorylation – NADH to NAD –ADP to ATP

Oxidative phosphorylation converts O 2 to H 2 0 (oxidative) converts O 2 to H 2 0 (oxidative) converts ADP to ATP (phosphorylation) converts ADP to ATP (phosphorylation) electron transport chain electron transport chain ubiquinones/cytochrome intermediates ubiquinones/cytochrome intermediates

Sugar as sole carbon source Pyruvate (C3) (C3)Acetate(C2) -CO 2 C6 Krebs Cycle C4 Pyruvate (C3) (C3) + CO 2

FATTY ACIDS AS SOLE CARBON SOURCE Fatty acids Acetate(C2) C6 Krebs Cycle C4 C4C2 + The glyoxylate cycle

. - + C3 C2 C4 C6 C2 C4 C5 C6

Krebs Cycle – biosynthetic – energy producing Removal of intermediates Removal of intermediates – must be replenished. Unique enzymatic replenishment pathway Unique enzymatic replenishment pathway – sugars – fatty 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 O 2 and must be protected from O 2 inactivation within the cell. 1.Respiration protection 2.Hetercyst formation 3.Membrane

Nitrogen reduction N 2 +8H + +8e - +16ATP  2NH 3 +H 2 +16ADP+16P i

Root Nodule Bacteria and Symbiosis with legumes Soybean root nodules Unnodulated soybean Nodulated soybean

Steps in the formation of root nodule in a legume infected by Rhizobium

Peptidoglycan synthesis Staphylococcus aureus Two carriers participate: uridine diphosphate (UDP) and bactoprenol Bactoprenol Bactoprenol 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-NAG 2.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 Cytoplasm Cell wall undecaprenol sugar aminoacid Cell Membrane

Peptidoglycan Synthesis Transport 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