Growth and Multiplication of Bacteria
Bacterial cell division- binary fission
- Most bacteria divide by binary fission in which the bacteria undergo cell division to produce two daughter cells identical to the parent cell.Bacterial DNA/chromosome- circular double stranded DNA
- Nuclear division followed by cell division.
- During binary fission, Two identical double strand DNA are separated and distributed to the daughter cells.
- Transverse septum grows across the cell from the cell membrane, followed by the deposition of cell wall material.
- Finally to daughter cell separates.
Bacterial growth curve
Bacteria growth follows a defined course .i.e. growth curve obtained by plotting bacterial count vs time. The bacterial growth curve has four phases.
- 1. Lag phase
- 2. Log/logarithmic/exponential phase
- 3. Stationary phase
- 4. Decline phase
| Lag Phase | Log phase | Stationary phase | Decline phase |
|---|---|---|---|
| -The period between inoculation and the beginning of multiplication is known as the lag phase. -In this phase, the organism adapts to the new environment. -During the lag phase, necessary enzymes, intermediate metabolites are built up in adequate quantity for multiplication to proceed/start. -Increase in size of a cell -Number of cells- not increase -Duration of phase depends on species, culture type and temperature. -At the end of the lag phase, the bacterium has maximum cell size. | -Cell division starts -A number of organism increase exponentially or by geometric progression with time. The straight curve between logarithm viable count versus time. -Cells are smaller and strain uniformly. | -After low phase bacterial growth ceases due to exhaustion of nutrient and accumulation of toxic products. -Number of progeny cell form is just enough to replace the number of cell that die. -Number of viable cells remain stationary as there is is almost balance between dying cell and new formed cell. -Cells are gram variable and show irregularity straining due to intracellular storage of granules. -Sporulation occurs -Many bacteria produce exotoxin this phase | -The stationary phase decline phase start due to exhaustion of nutrients accumulation of the toxic product and autolytic enzymes. -Bacterial population decline due to the death of cells. -Decline in viable count of the bacteria. -Involution forms are common. |
1. Lag phase
- Period between inoculation and the beginning of multiplication is known as the lag phase.
- In this phase, the organism adapts to the new environment.
- During lag phase, necessary enzymes, intermediate metabolites are built up in adequate quantity for multiplication to proceed/start.
- Increase in size of a cell
- Number of cells- not increase
- Duration of phase depends on species, culture type and temperature.
- At the end of the lag phase, the bacterium has maximum cell size.
2. Log/logarithmic/exponential phase
- Cell division starts
- A number of organism increase exponentially or by geometric progression with time.
- The straight curve between logarithm viable count versus time.
- Cells are smaller and strain uniformly.
3. Stationary Phase
- After low phase bacterial growth ceases due to exhaustion of nutrient and accumulation of toxic products.
- Number of progeny cell form is just enough to replace the number of cell that die.
- Number of viable cells remain stationary as there is is almost balance between dying cell and new formed cell.
- Cells are gram variable and show irregularity straining due to intracellular storage of granules.
- Sporulation occurs
- Many bacteria produce exotoxin this phase
4. Decline phase
- Stationary phase decline phase start due to exhaustion of nutrients accumulation of the toxic product and autolytic enzymes.
- Bacterial population decline due to the death of cells.
- Decline in viable count of the bacteria.
- Involution forms are common.
Bacteria count
Total Count
- Total number of bacteria whether they are living or dead.
- Total count is obtained by using counting chamber under microscope
Viable count
- Total number of living/viable cells
- The viable count is done by
- Dilution method
- plating method
Generation time
- Time required for a bacterium to give rise to two daughter cells under optimum condition is known Generation time.
- Generation time for most bacterium is 20 minutes
- Mycobacterium tuberculosis 20 hrs
- Mycobacterium lepre – 20 days
