Microbial Kinetics ( Prof.Dr. A.Coşkun DALGIÇ )


▪ Understanding the growth kinetics of microbial, animal, or plant cells is important for the design and operation of fermentation systems employing them. Cell kinetics deals with the rate of cell growth and how it is affected by various chemical and physical conditions.

▪ Unlike enzyme kinetics, cell kinetics is the result of numerous complicated networks of biochemical and chemical reactions and transport phenomena, which involves multiple phases and multicomponent systems.

▪ The heterogeneous mixture of young and old cells is continuously changing and adapting itself in the media environment which is also continuously changing in physical and chemical conditions. As a result, accurate mathematical modeling of growth kinetics is impossible to achieve. Even with such a realistic model, this approach is usually useless because the model may contain many parameters which are impossible to determine

▪ Various models can be developed based on the assumptions concerning cell components and population


If you inoculate unicellular microorganisms into a fresh sterilized medium and measure the cell number density with respect to time and plot it, you may find that there are six phases of growth and death.

1. Lag phase

2. Accelerated growth phase

3. Exponential growth phase

4. Decelerated growth phase

5. Stationary phase

6. Death phase

1. Lag phase: A period of time when the change of cell number is zero.

2. Accelerated growth phase: The cell number starts to increase and the division rate increases to reach a maximum.

3. Exponential growth phase: The cell number increases exponentially as the cells start to divide. The growth rate is increasing during this phase, is constant at its maximum value.

4. Decelerated growth phase: After the growth rate reaches a maximum, it is followed by the deceleration of both growth rate and the division rate.

5. Stationary phase: The cell population will reach a maximum value and will not increase any further.

6. Death phase: After nutrients available for the cells are depleted, cells will start to die and the number of viable cells will decrease.