Bacterial Reproduction
1- Occurs by binary fission (simple division) .
Process
*Slight enlargement in cell size due to :
1-Increase in metabolic activities
2-Production of energy and cell parts
3-DNA replicates (duplicated)
4-Cell wall and membrane grow inward separating DNA
5-Divides contents of cell and DNA molecules
6-Two daughter cells formed
GENERATION TIME
Time required for one cell to produce two new cells.
A-Varies with type organism and environmental conditions.
B-Average 15 - 20 min. (varies - 10 minutes to 24 hrs.)
MEASUREMENT OF BACTERIAL GROWTH
1-Optical density
2-Plate count
3-Direct microscopic count
Phases of growth
In autecological studies, bacterial growth in batch culture can be modeled
with four different phases: lag phase (A), exponential or log phase (B),
stationary phase (C), and death phase (D).
Growth is shown as L = log(numbers) where numbers is the number of
colony forming units per ml, versus T (time.)
1. During lag phase, bacteria adapt themselves to growth conditions. It is
the period where the individual bacteria are maturing and not yet able
to divide. During the lag phase of the bacterial growth cycle, synthesis
of enzymes and other molecules occurs, no increase in number of
cells.
2. Exponential phase (sometimes called the log phase or the logarithmic
phase) is a period characterized by cell doubling. The number of new
bacteria appearing per unit time is proportional to the present
population. The slope of this line is the specific growth rate of the
organism, which is a measure of the number of divisions per cell per
unit time.
3. The "stationary phase" is due to a growth-limiting factor; this is mostly
depletion of a nutrient, and/or the formation of inhibitory products such
as organic acids. Rate of growth influenced by environmental factors.
Stationary Phase - rate of reproduction = rate of death. Due to exhaustion
of nutrients, accumulation of wastes.
4- At death phase, bacteria run out of nutrients and die. rate of death 
rate of reproduction.Some species die quickly, others survive longer.
Sporulation
The sporulation process begins when nutritional conditions become
unfavorable, near depletion of the nitrogen or carbon source (or both)
Many environmental bacteria are able to produce stable dormant, or
resting, forms as a branch of their life cycle to enhance their survival
under adverse conditions. Such dormant forms are called endospores,
cysts, or heterocysts (primarily seen in cyanobacteria), depending on the
method of spore formation, which differs between groups of bacteria.
Sporulation involves the production of many new structures, enzymes,
and metabolites along with the disappearance of many vegetative cell
components. These changes represent a true process of differentiation: A
series of genes whose products determine the formation and final
composition of the spore are activated.
Germination
The germination process occurs in three stages: activation, initiation, and
outgrowth:
Activation
Most endospores cannot germinate immediately after they have formed.
But they can germinate after they have rested for several days or are first
activated, in a nutritionally rich medium, by one or another agent that
damages the spore coat. Among the agents that can overcome spore
dormancy are heat, abrasion, acidity, and compounds containing free
sulfhydryl groups.
Initiation
Once activated, a spore will initiate germination if the environmental
conditions are favorable. Different species have evolved receptors that
recognize different effectors as signaling a rich medium: Thus, initiation
is triggered by L-alanine in one species and by adenosine in another.
Outgrowth
Degradation of the cortex and outer layers results in the emergence of a
new vegetative cell consisting of the spore protoplast with its surrounding
wall. Outgrowth requires a supply of all nutrients essential for cell
growth.