Transcript Bacterial Growth and Reproduction

Bacterial Growth
and Reproduction
Asexual Reproduction
- Binary Fission
• Form of asexual
reproduction
• Results in identical
genetic material in both
cells
• Most common form of
reproduction in bacteria
Binary Fission
DNA
Bacteria
Binary Fission
Step 1:
The bacterial
cell elongates.
Binary Fission
Step 2:
The DNA is
replicated.
Binary Fission
Step 3: The
cell wall and
cell
membrane
begin to form.
Binary Fission
Step 4: The
cell wall and
cell
membrane
begin to form.
Binary Fission
Step 5: Cells
separate.
Binary fission creates
no genetic variation!
It’s just a clone.
Sexual Reproduction &
Transfers
• Bacteria can get
variation in their genes
by:
– sexual reproduction conjugation
– transformation/gene
transfer
Sexual Reproduction Conjugation
• Not common in bacteria,
however conjugation does
occur among some bacteria,
such as E. coli and Salmonella
Sex Pili
• In conjugation, the donor and
recipient bacteria make
contact by means of the sex
pilus, where plasmids are
transferred, giving the
recipient an altered set of
characteristics
*Recall – a plasmid is a loop of DNA that is separate
from the main chromosome in the bacteria
Conjugation
Step 1: A sex
pilis forms.
Conjugation
Step 2: The
plasmid
replicates and
travels to the
other cell.
c
Conjugation
Step 3: The
cells separate.
c
Transformation
• Bacteria picks up genetic material from the
environment in the form of plasmids or fragments of
DNA
• Recall – a plasmid is a
loop of DNA that is
separate from the
main chromosome in
the bacteria
Transformation
with DNA
Free-floating
DNA
DNA
Bacteria
Transformation
with DNA
The bacterial
cell uptakes
the DNA.
Transformation
with DNA
The free-floating
DNA and the
bacterial DNA
combine.
Transformation
with Plasmid
Plasmid
DNA
Bacteria
Transformation
with Plasmid
The free-floating
plasmid enters the
bacteria.
Recap: Reproduction & Exchange of
Genetic Information
Type of
Reproduction or
Exchange of
Genetic
Information
What is it?
Creates new
bacteria?
Creates genetic
diversity?
Binary Fission
Asexual
reproduction
Yes
No genetic
diversity
Bacterial
Conjugations
Sharing of a
plasmid from one
bacterium to
another
No
Yes, creates
genetic diversity
Bacterial
Transformations
Picking up a
plasmid from the
environment
No
Yes, creates
genetic diversity
Unfavourable Conditions
• During unfavourable conditions,
some bacteria survive by forming
dormant or resting cells, called
endospores.
• Endospores are resistant to heat and
other extreme conditions, and
cannot be easily destroyed
• When suitable conditions return, the
endospore sprouts and an active
bacterium emerges.
• A thickened cell wall forms around
the genetic material and cytoplasm.
The remainder of the original cells
eventually disintegrates.
Endospores
Growth Curves
Generation Time: The time required for a cell to
divide or a population to double
• Most bacteria have a doubling time of 1-3 hours,
although some may be greater than 24 hours
• Example: E. coli has a doubling time of 20 minutes
• Bacterial division occurs according to a
logarithmic progression (two cells, four cells,
eight cells, etc.).
Growth Phases
• During the lag phase, there is little or no change in the
number of cells, but metabolic activity is high.
– Bacteria are adjusting to their new surroundings.
• During the exponential growth phase, the bacteria
multiply at the fastest rate possible under the
conditions provided.
• During the stationary phase, there is equilibrium
(balance) between cell division and death.
– Nutrients are exhausted and waste products build up
• During the death phase, the number of deaths exceeds
the number of new cells formed.