Bacteria multiply through a process called binary fission. They go through distinct growth phases including a lag phase where they adapt to new environments, an exponential or log phase where rapid cell division occurs, a stationary phase where growth balances death, and a death phase. Gram-positive bacteria have a thick peptidoglycan layer while gram-negative bacteria have a thinner peptidoglycan layer between the inner and outer membranes.
3. Bacterial Growth and Multiplication
• Transverse or Binary cell division
Growth of bacteria can be separated into two distinct stages
1. An increase in cell mass such as elongation of a bacillus, or an
increase in size or volume such as in occurs
2. The division of these cells into two daughter cells
The most common mechanism of bacterial cell division which ca
n be described as Binary or transverse division.
4. Reproduction
• Prokaryotic cell division is bi
nary fission.
• Single DNA molecule that
first replicates.
• Attaches each copy to a di
fferent part of the cell me
mbrane.
• Cell begins to pull apart.
• Following cytokinesis, the
re are then two cells of id
entical genetic compositio
n.
5. The bacterial growth curve
• When bacterium is seeded into a suitable liquid medium and incuba
ted, its growth shows a definite course.
• If bacterial growth measurements are made at intervals after inocul
ation and plotted in relation to time, a growth curve is obtained. Th
e curve shows the following phases.
• Lag Phase
• Log Phase
• Stationary Phase
• Death Phase
6. Bacterial growth
•Lag phase
• This phase of growth occurs when cells are transferred from o
ne medium to another or one environment to another.
• It is a phase of adjustment and represents the period required
for the adaptation of the cells to new environment.
• The cells in this phase often increase in total volume almost t
wo or threefold, but they do not divide.
• These cells are rapidly synthesizing DNA, new proteins and ne
w enzymes as a prerequisite to division.
7. Exponential phase
• – or log phase
• In this phase, cells are dividing at both a constant rate as well as ma
ximum rate.
• Cellular component such as RNA, protein, dry weight, and cell wall
polymers are also increasing at a constant rate, they are much small
er in diameter than cells in the lag phase.
• The exponential growth phase usually comes to an end because of
depletion of essential nutrients, depletion of oxygen in culture or th
e accumulation of toxic products.
8. Stationary phase
• During this phase, there is a rapid decrease in the rate of cell d
ivision. Eventually, the total number of dividing cells will equal
the number of dying cells, a true stationery cell population occ
urs.
• The cells then direct their resources towards survival energy g
eneration is harnessed to maintain osmotic barriers, mobility,
and the repair and synthesis of essential macromolecules.
• The energy required to maintain cells in stationery phase is cal
led Maintenance energy and is obtained from the degradation
of cellular storage products.
• After all of the storage products are exhausted, the cells then
degrade their cellular components, which ultimately leads to d
eath phase.
9. Death Phase
• In this stage, the cells reproduce more slowly, and death overt
akes them in increasing numbers.
• The cells eventually enter the logarithmic death phase, during
which the decrease in the number of cells occurs at a regular,
unchanging rate, a rate that approximates that of the exponen
tial growth phase but is of negative slope.
