Stoichiometry of Cell Growth and Kinetics

 

Definition:

• Describes the balanced chemical equation for the formation of biomass from substrates like carbon, nitrogen, and oxygen.

• Helps determine nutrient requirements and product yields in a bioprocess.

Stoichiometry of Cell Growth:

Definition:

• Describes the balanced chemical equation for the formation of biomass from substrates like carbon, nitrogen, and oxygen.

• Helps determine nutrient requirements and product yields in a bioprocess.

Key Components:

1. Substrate (Carbon Source):

• Usually glucose or other carbohydrates.

2. Biomass (Cells):

• Represented as CxHyOzNnwhere x, y, z, and n vary depending on the organism.

3. Products:

• Primary metabolites: CO₂, H₂O, and other cellular by-products.

4. Oxygen:

• Required for aerobic growth.

Example Stoichiometric Equation:

• For aerobic growth of E. coli on glucose:

Significance:

• Predicts biomass yield and by-product formation.

• Balances carbon, nitrogen, and energy requirements.

• Helps in scaling up bioprocesses for industrial applications.

Cell Growth Kinetics:

Definition:

• Describes the rate of increase in cell number or biomass over time.

• Key to optimizing bioreactor performance and understanding microbial behavior.

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Growth Phases in a Batch Culture:

1. Lag Phase:

• Cells adapt to the new environment; no significant growth.

2. Log (Exponential) Phase:

• Rapid cell division; growth rate reaches its maximum (μmax​).

3. Stationary Phase:

• Nutrients deplete, and growth slows; growth rate = death rate.

4. Death Phase:

• Cells die due to nutrient exhaustion and toxic by-products.

Key Kinetic Parameters:

1. Specific Growth Rate (μ):

• Definition: Rate of increase of biomass per unit biomass concentration.

• Formula:

1. 

2. Doubling Time (td​):

• Time required for the biomass to double.

• Formula:

• td=ln(2)μ

Types of Growth Models:

1. Batch Culture:

• Closed system; all nutrients provided at the start.

• Growth follows a predictable curve (lag, log, stationary, death).

2. Continuous Culture (Chemostat):

• Open system; fresh medium continuously added, and culture removed.

• Growth maintained at a steady state.

3. Fed-Batch Culture:

• Nutrients are added gradually to prolong the log phase.

• Common in industrial fermentations.

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Conclusion:

• Stoichiometry of cell growth is crucial for understanding nutrient consumption and product formation in bioprocesses.

• Growth kinetics helps optimize conditions for maximum productivity, ensuring efficient use of resources.

• Together, they provide the foundation for designing and scaling up fermentation processes in biotechnology and industrial microbiology.