Bacterial Growth and Energy Metabolism

Bacterial Growth and Energy Metabolism

• 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.

Measuring Bacterial Growth

• 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.

Bacterial Growth Curve

• 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

Generation and Generation Time

• Generation: Time interval for two cells formed from one.
• Generation time: Time required for this to occur

Keywords: Metabolism

• 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.

Oxidation/Reduction

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

Metabolism by Enzymes

• Enzymes accelerate metabolic reactions by lowering activation energy.

Energy in Redox Reactions

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

Glycolysis

• 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.

Regulation of Glycolysis

• Glycolysis is regulated by molecules like ATP, AMP, and citrate.

TCA Cycle (Citric Acid Cycle, Krebs Cycle)

• 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

Regulation of TCA cycle

• The TCA cycle is regulated by the presence of ATP and other molecules

Fermentation

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

Ethanol Fermentation

• A fermentation process, in yeast, that generates ethanol and CO2 from glucose.

Electron Transport System

• 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

Oxidative Phosphorylation

• Using proton motive force for ATP production.

ATP Synthesis

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