BIO 411 - Medical Microbiology Chapter 4 Bacterial Metabolism and Growth

Metabolic Requirements Bacteria’s first priority – Survive and Reproduce To do this they need: Source of Energy (for human pathogens sugars, fats, and proteins) Raw materials to build all cell structures Carbon source Nitrogen source Water Ions Table 4-1

Metabolic Requirements Different O2 needs: Obligate anaerobes (Clostridium perfringens, and others) Obligate aerobes (Mycobacterium tuberculosis) Facultative anaerobes (most bacteria)

Metabolic Requirements Differences is metabolic requirements: E. coli Treponema pallidum

Overview of Metabolism Metabolism = the sum of all chemical processes within a cell Consists of: Catabolism - breakdown of nutrients for energy and building blocks (precursor metabolites) Anabolism - building of cellular components using energy and building blocks These both occur through metabolic pathways Overview of bacterial metabolism. (extracellular digestion, etc.)

Metabolism of Glucose (cont.) Bacteria can catabolize glucose by (in order of decreasing efficiency): Respiration - Final electron acceptor in the electron transport chain is an inorganic molecule Aerobic - O2 is the final e- acceptor Anaerobic - something else is (NO3-, SO42- , CO2 ) Fermentation - final electron acceptor is an organic molecule

Respiration Deals with three metabolic pathways: Glycolysis (Embden-Meyerhof-Parnas) TCA cycle (also called the Krebs Cycle and the citric acid cycle) Electron Transport System

Respiration (cont.) Glycolysis: Figure 4-2 1 glucose molecule is split into 2 molecules of pyruvate 2 ATP are gained for every glucose molecule 2 NADH are produced for every glucose molecule NADH picks up high-electrons lost by glucose Figure 4-2

Respiration (cont.) Conversion of pyruvate to acetyl-CoA pyruvate cannot enter directly into the TCA cycle 1 NADH is produced for every pyruvate 1 molecule of CO2 is release for every pyruvate

Respiration (cont.) TCA cycle: cyclic metabolic pathway produces 1 ATP for every acetyl-CoA produces 3 NADH for every acetyl-CoA produces 1 FADH2 for every acetyl-CoA All 6 carbons from the original glucose molecule have been converted to CO2 by the end of the TCA cycle Figure 4-4

Respiration (cont.) Electron Transport System All NADH molecules formed in the previous steps bring the electrons they have gained to the electron transport system These electrons are passed along a series of membrane proteins eventually the electrons are given to the final e- acceptor (O2 to form H2O, etc.) Figure 4-5

Respiration (cont.) These proteins use the energy of the electrons to pump protons across the membrane (from the inside of the cell to the outside) This pumping of protons across the membrane generates an electrochemical gradient across the membrane These protons are then brought back through the membrane and the associated energy is used to produce ATP Analogy involving a dam

Respiration (cont.) One molecule of glucose can produce 38 ATP through this complete process Figure 4-6

Aerobic vs. Anaerobic Respiration If oxygen is the final electron acceptor, the process is called aerobic respiration If some other molecule is the final electron acceptor, the process is called anaerobic respiration sulfate reducers, nitrate reducers, methane bacteria

Fermentation Fermentation begins with glycolysis Fermentation usually occurs under anaerobic conditions (no oxygen = no final electron acceptor) Problem: 2 NADH don’t give off e- at the ETS NADH build-up would eventually shut down glycolysis Fermentation unloads electrons on pyruvate or a derivative of pyruvate this regenerates NAD+ so glycolysis can continue Figures 4-1 and 4-3

Lipid Catabolism Lipids are broken down to glycerol and fatty acids Glycerol enters glycolysis Fatty acids undergo beta-oxidation to form acetyl-CoA Figure 4-1

Protein Catabolism Proteins are broken down outside the cells by protease enzymes. The amino acids are brought inside the cells and funnel into glycolysis or the Krebs cycle Figure 4-1

Anabolism What is anabolism? Anabolism also occurs through metabolic pathways Many times it’s just the opposite of protein, lipid and carbohydrate catabolism Figures 4-1 and 4-7

Disease of the Day Dental Caries (cavities) Etiology – Streptococcus mutans Reservoir – Our Mouthes (normal flora) Transmission and Development Transmission – NA Development Importance of sucrose (Figure 25.3)

Disease of the Day Prevention and Control Brushing/Flossing Fluoride Decrease sucrose intake