Unit 2: Bacterial Metabolism and Fermentation

Fermentation and Pasteurization Pasteur showed that microbes are responsible for fermentation Fermentation is the conversion of sugar to alcohol or acid Fermentation is used to make cheese, yogurt, beer and wine Microbial growth is also responsible for spoilage of food Bacteria that use alcohol and produce acetic acid spoil wine by turning it to vinegar (acetic acid) and bacteria that utilize lactose to produce lactic acid transform milk into yogurt

Fermentation and Pasteurization Pasteur demonstrated that these spoilage bacteria could be killed by heat that was not hot enough to evaporate the alcohol in wine Pasteurization is the application of a high heat for a short time Figure 1.4

A Nutritional Classification of Organisms Other energy sources include electricity, nuclear or thermal. Figure 5.28

A Nutritional Classification of Organisms Figure 5.28

A Nutritional Classification of Organisms Figure 5.28

Metabolic Diversity among Organisms Nutritional Type Energy Source Carbon Source Example Photoautotroph Light CO2 Oxygenic: Cyanobacteria plants Anoxygenic: Green, purple bacteria Photoheterotroph Organic compounds Green, purple nonsulfur bacteria Chemoautotroph Chemical Iron-oxidizing bacteria Chemoheterotroph Fermentative bacteria Animals, protozoa, fungi, bacteria.

Carbohydrate Catabolism The breakdown of carbohydrates to release energy Glycolysis Krebs cycle Electron transport chain

A 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 (rather an inorgainc molecules containing sulfate, nitrate, nitrite, carbonate, etc..). Yields less energy than aerobic respiration because only part of the Krebs cycles operates under anaerobic conditions.

Glycolysis The oxidation of glucose to pyruvic acid produces ATP and NADH

Preparatory Stage of Glycolysis 2 ATP are invested Glucose is split to form 2 glucose-3 -phosphate Figure 5.12, steps 1–5

Cellular Respiration Oxidation of molecules liberates electrons for an electron transport chain ATP is generated by oxidative phosphorylation

Energy-Generating Stage of Glycolysis 2 glucose-3-phosphate oxidized to 2 pyruvic acid 4 ATP produced 2 NADH produced Figure 5.12, steps 6–10

Overall Result of Glycolysis Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+  2 pyruvic acid + 4 ATP + 2 NADH + 2H+

Intermediate Step Pyruvic acid (from glycolysis) is oxidized and decarboyxlated Figure 5.13

Acetyl CoA

The Krebs Cycle

Carbohydrate Catabolism Pathway Eukaryote Prokaryote Glycolysis Cytoplasm Intermediate step Krebs cycle Mitochondrial matrix ETC Mitochondrial inner membrane Plasma membrane

The Electron Transport Chain A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain Energy released can be used to produce ATP by chemiosmosis

Chemiosmotic Generation of ATP Figure 5.16

An Overview of Chemiosmosis Figure 5.15

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 Scientific definition: Releases energy from oxidation of organic molecules Does not require oxygen Does not use the Krebs cycle or ETC Uses an organic molecule as the final electron acceptor

Figure 5.11

An Overview of Fermentation Figure 5.18a

Fermentation Alcohol fermentation: Produces ethanol + CO2 Lactic acid fermentation: Produces lactic acid Homolactic fermentation: Produces lactic acid only Heterolactic fermentation: Produces lactic acid and other compounds

Types of Fermentation Figure 5.19

End-Products of Fermentation Figure 5.18b

A Fermentation Test Figure 5.23

Types of Fermentation Table 5.4

Types of Fermentation Table 5.4

Requirements of ATP Production Figure 5.27