1. BIO 411 - Medical Microbiology
Chapter 4
Bacterial Metabolism and Growth

2. 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

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

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

5. 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.)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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)

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