4 5-microbial nutrition and culture (2)

Metabolism cont’d

Carbohydrate Catabolism

Carbohydrate Catabolism cont’d

Summary of Carbohydrate Catabolism

TCA Cycle (Krebs Cycle)

• 2 acetyl-CoA groups are oxidized in the Krebs cycle for each glucose molecule (1 six-carbon glucose is oxidized to two 3 carbon pyruvic acid molecules, each of which is decarboxylated to produce an acetyl-CoA molecule). 

• Electrons are picked up by NAD+ and FAD for the electron transport chain.

• From one molecule of glucose, oxidation in the Krebs cycle produces 6 molecules of NADH, 2 molecules of FADH2, and 2 molecules of ATP.

• Decarboxylation produces 6 molecules of CO2.

TCA Cycle (Krebs Cycle)

Electron Transport Chain• As electrons are passed from carrier to carrier

in the chain, they decrease in energy and some of the energy lost is harnessed to make ATP

In aerobic prokaryotes, 38 ATP molecules can be produced form complete oxidation of a glucose molecule in glycolysis, the Krebs cycle, and the electron transport chain. In eukaryotes, 36 or 38 ATP molecules are produced from complete oxidation of a glucose molecule (in some tissues 2 ATP are required to shuttle the 2 electrons from the NADH produced in glycolysis across the mitochondrial membrane to the electron transport chain, in others there is no energy cost and 38 ATP are gained per mole of glucose).

Summary

Summary of Respiration

• Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen O2

• Anaerobic respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycle operates under anaerobic condition

Anaerobic Respiration

• Electron acceptors other than oxygen are used i.e.:

• Inorganic oxygen containing molecules such as Nitrate (NO3

-), Sulfate (SO42-), Ferric iron (FE3

+), Carbonate (CO3

2-) and Perchlorate (ClO4-)

• Less energy is released• Permits microorganisms to respire in anoxic

environments

Fermentation

• Any spoilage of food by microorganisms (general use)

• Any process that produces alcoholic beverages or acidic dairy products (general use)

• Any large scale microbial process occurring with or without air (common definition used in industry)

Fermentation cont’d

• Scientific definition

1. Release of energy from organic molecules

2. Does not require oxygen

3. Does not use the Krebs cycle of Electron transport chain

4. Uses organic molecule as the final electron acceptor

Types of Fermentation

PRODUCT APPLICATION ORGANISM

Bacitracin Antiobiotic Bacillus subtilis (bacterium)

Chloramphenicol AntiobioticStreptomyces venezuelae (bacterium)

Citric acid Food flavoring Aspergillus niger (fungus)

Erythromycin Antibiotic Streptomyces erythaeus (bacterium)

Invertase Candy Saccharomyces cerevisiae (fungi)

Lactase Digestive aid Escherichia coli (bacterium)

Neomycin Antibiotic Streptomyces fradiae (bacterium)

Pectinase Fruit juice Aspergillus niger (fungus)

Penicillin Antibiotic Penicillium notatum (fungus)

Riboflavin Vitamin Ashbya gossypii (fungus)

Streptomycin Antibiotic Streptomyces griseus (bacterium)

Subtilisins Laundry detergent Bacillus subtilis (bacterium)

Tetracycline AntibioticStreptomyces aureofaciens (bacterium)

Fermentations By Naturally-Occurring Organisms

PRODUCT APPLICATION ORGANISM

B. growth hormone Milk production(cows)Escherichia coli (E. coli)

Cellulase Cellulose E. coli

H. growth hormone Growth deficiencies E.coli

Human insulin Diabetics E. coli

Monoclonal antibodies Therapeutics Mammalian cell culture

Ice-minus Prevents ice on plants Pseudomonas syringae

Sno-max Makes snow Pseudomonas syringae

t-PA Blood clots Mammalian cell culture

Tumor necrosis factor Dissolves tumor cells E.coli

Fermentations By Genetically Engineered Organisms

Fermentation

• Alcohol fermentation: Produces ethanol and CO2

• Lactic acid fermentation: Produces lactic acid

-homolactic fermentation: Produces lactic acid only

-heterolactic fermentation: Produces lactic acid and other compounds

Final Electron Acceptor

Oxygen

• O2

• Aerobic respiration

Other inorganic molecules

• (NO3-), (SO4

2), (FE3

+), (CO32-)

& (ClO4-)

Anaerobic respiration

Organic molecules

• Pyruvic acid• Fermentation

Final electron acceptor

Electron carriers

Electron