Bacterial Growth and Energy Metabolism

Study Notes

Bacterial growth is measured in several ways
CFU (Colony Forming Unit): A method for estimating the number of bacteria in a sample. A measured sample is diluted and a small aliquot plated. The number of colonies is counted, and mathematical calculation of the concentration in the original sample completed.

Dilution Method (CFU):
- A sample is serially diluted (1/10, 1/100, etc.)
- A set amount of each dilution is plated.
- Colonies are counted on the plated samples.
- The count is used to compute the total number of bacteria in the original sample.
- Calculation factors are used for the dilution
Petroff-Hausser Counting Chamber:
- A microscopic method used for bacterial counting.
- Cells in a grid are counted.
- A mathematical calculation determines the concentration of bacterial cells
Optical Density:
- A method that measures the turbidity (cloudiness) of a bacterial culture.
- A spectrophotometer is used.
- Data are used to compute the concentration indirectly.

A graphical representation of bacterial growth over time.
Stages: Lag, Exponential, Stationary, Death
Lag Phase: Initial adaptation period; enzymes synthesis; no bacterial reproduction; growth rate=0.
Exponential Phase: Rapid cell division, constant growth rate, uniform characteristics
Stationary Phase: Nutrient depletion and toxin buildup; cell growth stops; cell death rate = cell growth rate
Death Phase: Cell death due to nutrient exhaustion or toxin accumulation

Metabolism (Catabolism vs. Anabolism): All chemical reactions in a bacterial cell.
Enzymes: Biological catalysts that speed up metabolic reactions.
Oxidation/Reduction: Redox reactions involve electron transfer in metabolic processes
Glycolysis: Metabolic pathway breaking glucose into pyruvate, producing ATP and NADH.
Substrate-level Phosphorylation: Producing ATP directly from substrates in metabolic pathways.
Fermentation: Metabolic process occurring in the absence of oxygen, producing ATP and various end products.
TCA cycle: A metabolic pathway that further oxidizes pyruvate, producing more ATP, NADH, FADH2
Electron Transport System: Electron carriers transfer electrons to produce a proton gradient used for ATP production.
ATP synthase: An enzyme that produces ATP using the proton gradient established by the electron transport chain.

Chemistry: Oxidation = losing electron. Reduction = gaining an electron.
Biology: Oxidation = losing hydrogen atom. Reduction = gaining hydrogen atom.

Redox reactions produce energy stored in certain compounds with energy rich phosphate bonds. (ATP = prime example)

Overview: C6H12O6 + 2ADP + 2PO43- + 2NAD+ → 2C3H3O3 (pyruvate) + 2ATP + 2NADH + 2H+ + 2H2O
Two pyruvate molecules are produced from one molecule of glucose.
Two ATP and two NADH molecules are also produced
No CO2 is produced
Glycolysis occurs in the cytoplasm.

Overview: 2C3H3O3(pyruvate) +2ADP + 2P; +8NAD+ + 2FAD + 4H2O → 6CO2 + 2ATP + 8NADH + 2FADH2
One molecule of pyruvate produces 3 molecules of CO2.
Four molecules of NADH, 1 molecule of FADH2, and 1 molecule of ATP are also produced

Energy is produced by anaerobic glycolysis; NADH is oxidized while fermentation products are formed.
Important for certain food industries.

Three major functions in bacterial cell walls:
- Permeability barrier: Prevents leakage and controls nutrient transport.
- Protein anchor: Attaches proteins involved in transport, bioenergetics, and chemotaxis.
- Energy conservation: Generates and uses proton motive force

Fo subunit is sensitive to oligomycin
ATP Synthase (Complex V): An enzyme that produces ATP (using a proton gradient) during oxidative phosphorylation.