Bacterial Reproduction
Lecture #
Dr. Sobia Manzoor
Introduction:
• Bacteria
(singular:
bacterium)
prokaryotic micro organisms.
• Few micrometers in length,
• Have a number of shapes, ranging
from spheres to rods and spirals.
• Were among the first life forms to
appear on Earth,
• Inhabits soil, water, acidic hot
springs, radioactive waste and the
deep portions of Earth’s crust.
• Bacteria also live in symbiotic
and parasitic relationships with
plants and animals.
Acidic hot springs
Reproduction /procreation:
• A Biological process by which new "offspring"
individual organisms are produced from their
"Parents".
• A fundamental feature of all known Life
• Each individual organism exists as the result of
reproduction
• Biologically dead or biologically alive
Mule (offspring of a male donkey and a female
horse)
Methods of reproduction
• Broadly grouped into two main types
• Sexual and Asexual
• Asexual reproduction:
an individual can reproduce without involvement
with another individual of that species.
• Not limited to single celled organisms.
• Most plants have the ability to reproduce
asexually.
• Sexual reproduction: typically requires the
involvement of two individuals or gamestes , one
each from opposite type of sex.
I. Asexual Reproduction:
• Mostly by asexual reproduction
• which is a mode of reproduction by which offspring
arise from a single organism, and inherit the genes of
that parent only
• Under ideal conditions, lots of food, proper
temperature and lots of space, bacteria divide every 20
minutes and in 24 hours a single bacterial cell could
produce 2 million kg of bacterial cells.
Binary Fission
Spore formation
1.Binary Fission
• When a cell has almost doubled in
size it will replicate its DNA and
divide in half
• This produces 2 genetically identical
daughter cells – clones
• cell divides exactly in half
– single cell division
– reproduction of the entire organism
– form of asexual reproduction
• Asexual reproduction does not involve
the exchange of genetic material
• Binary fission is the evolutionary
precursor to mitosis
E. coli undergoing cell division
2.Spore Formation
• Bacteria form spores during unfavorable
conditions
• One type is called an endospore
–Cell forms a thick internal wall that encloses its DNA
• Spores can remain dormant for months until
conditions improve
Endospore Germination
• The transformation of dormant spores into active
vegetative cells seems almost as complex a process as
sporogenesis.
• It occurs in three stages:
– activation,
– germination, and
– outgrowth
• Activation is a process that prepares spores for germination
and usually results from treatments like heating.
• It is followed by germination process is characterized by
spore swelling, rupture or absorption of the spore coat, loss
of resistance to heat and other stresses, release of spore
components, and increase in metabolic activity.
• Outgrowth; cell prepare for division
II. Sexual reproduction:
• Sexual reproduction is a process that creates a
new organism by combining the genetic material
of two organisms.
• Genetic recombination is responsible for
generating diversity within bacterial populations
• There present 3 types of sexual reproduction in
bacteria
1. Conjugation
2. Transduction
3. Transformation
1.Conjugation:
"Conjugation is the direct transfer of
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genetic material between two bacterial
cells that are temporarily joined.
It resembles sexual reproduction,
Two bacteria join (mate) and exchange
genes.
Conjugation is a ‘one way’ transfer of
DNA.
DNA is transferred from one cell
(donor) to another (recipient)
The DNA donor uses appendages
called sex pili to attach to the recipient.
This is followed by the formation of a
cytoplasmic bridge for which DNA can
be transferred through, and promote
recombination.
2. Transduction
• Phages (viruses that infect
bacteria) carry bacterial genes
from one host cell to another as a
result of mistakes in the phage
reproductive cycle
• Bacterial DNA found in the phage
is transferred to the new host
and is incorporated into the host
genome
• In the process called generalized
transduction, this transfer is
random
3.Transformation:
• Living cells take up DNA
from their environment.
• A foreign gene is
incorporated into a bacterial
chromosome by replacing the
native allele.
• The transformed cell now has
a chromosome/plasmid
containing DNA from two
different cells.
• Many bacteria possess cell
surface proteins that facilitate
transformation in natural
populations
• E. coli is used in
biotechnology applications of
genetic recombination