What is cell growth?
Growth is a result of both cell division and a change in cell growth
Cell growth phases
- Lag phase
- Exponential phase
- Deceleration phase
- Stationary phase
- Death phase
When does the lag phase take place?
Directly after innoculation
What happens during the lag phase?
- Microorganisms reorganize their molecular constituents
- Enzymes are synthesized or repressed
- Inoculum adapt to the new environment
What happens during the exponential phase?
- Cells have adjusted to new environment
- Cell number density and cell mass increase exponentially with time
- Balanced growth occurs
- Cell metabolism is set up to achieve maximum rates of reproduction
What happens during the deceleration growth phase?
- Growth starts to decelerate due to the depletion of essential nutrients and the accumulation of toxic by-products
- The rapidly changing environment results in unbalanced growth
- Cell is restructured to increase the prospects of cellular survival in a hostile environment
What happens during the stationary phase?
- Net growth rate is equal to zero
- Growth rate = death rate
- Cells are still metabolically active and produce secondary metabolites
- Total cell mass concentration stays constant, but number of viable cells decrease
- Cell lysis occurs (cryptic growth)
- No growth, but secondary metabolite production (antibiotics, hormones).
What happens during the death phase?
- Difficult to differentiate between stationary phase and death
- Depletion of nutrients or toxic product accumulation
Three major categories of microbial growth
Growth associated product formation
Non-growth associated product formation (specific production rate is constant)
Mixed growth associated product formation
What happens during growth associated product formation?
Products form simultaneously with the microorganisms
When does non-growth related product formation take place?
During the stationary phase when growth rate = 0
When does mixed growth associated product formation take place?
During the slow growth phase and the stationary phase
