Bacteria are the simplest, the smallest, and the most successful microorganisms.
They were first discovered by Anton Leeuwenhoek (1676).
In the five kingdom classification, they are placed in Kingdom Monera. Reproduction: Vegetative Reproduction, Sexual Reproduction & Asexual Reproduction.
A Critique of the Proposed National Education Policy Reform
Reproduction in bacteria
1. Reproduction in Bacteria
Sr. Kaslin Juliat SAL
Assistant Professor
St. Xavier’s College
Mahuadanr
Nilamber Pitamber University
2. Bacteria are the simplest, the smallest, and the most
successful microorganisms.
They were first discovered by Anton
Leeuwenhoek (1676).
In the five kingdom classification, they are placed in
Kingdom Monera.
5. In Bacteria a small protuberance, called bud, develops
at one end of the cell.
Genome replication follows, and one copy of the
genome gets into the bud.
Then the bud enlarges, eventually become a daughter
cell and finally gets separated from the parent cell.
Budding
6. Mostly during unfavorable conditions, bacterial
protoplasm undergoes compartmentalization and
subsequent fragmentation, forming minute bodies
called gonidia.
Under favorable conditions, each gonidium grows to
a new bacterium. It becomes apparent that prior to
fragmentation the bacterial genome has to undergo
repeated replication so that each fragment gets a copy
of it.
Fragmentation
7. It is the common type of reproduction under favorable conditions
in which cell divides into two similar daughter cells.
During the process, the bacterial chromosomes get attached to the
cell membrane and replicates to the bacterial chromosomes.
As the cell enlarges the daughter chromosomes gets separated. A
cross wall is formed between the separating daughter
chromosomes.
It divides the cell into two daughter cells. The daughter cells soon
grow to maturity within 20-30 minutes.
Under favorable conditions many bacteria divide once in 20-30
minutes.
Binary fission
9. Endospore are resting spores formed in some gram positive
bacteria (Bacillus and Clostridium) during unfavourable
conditions. They are formed within the cells.
During this process a part of the protoplast becomes concentrated
around the chromosome. A hard resistant wall is secreted around
it.
The rest of the bacterial cell degenerates; Endospore are very
resistant to extreme physical conditions and chemicals.
During favorable conditions the spore wall gets ruptured and the
protoplasmic mass gives rise to a new bacterium.
Endospore formation
10.
11. Sexual reproduction occurs in the form of genetic
recombination.
There are three main methods of Genetic
Recombination
Sexual reproduction
Sexual
reproduction
Transformation
Transduction
Conjugation
12. Conjugation
•Bacteria showing conjugation are dimorphic, i.e., they
have two types of cells, male (F+) or donor and female
(F-) or recipient.
•The male or donor cell possesses 1-4 sex pili on the
surface and fertility factor (transfer factor, sex factor) in
its plasmid. Fertility factor contains genes for producing
sex pili and other characters needed for gene transfer.
•Sex pili are 1- 4 narrow protoplasmic outgrowths. Both
sex pili and fertility factor are absent in female or
recipient cells.
13. If these two types of cells
happen to come nearer, a
piles of male cell establishes
a protoplasmic bridge or
conjugation tube with the
female cell.
It takes 6-8 minutes. Gene
exchange can occur by two
methods.
14. Transformation
It is the absorption of DNA segment from the surrounding
medium by a living bacterium.
The phenomenon was discovered by Griffith in 1928. Its
mechanism was worked out by Avery (1944).
Receptivity for transformation is present for a brief period when
the cells have reached the end period of active growth.
At this time they develop specific receptor sites in the wall.
Normally E. coli does not pick up foreign DNA but it can do so
in the presence of calcium chloride.
15. Transduction
•It is the transfer of foreign genes by means of viruses.
•The process also occurs in E. coli and a number of other hosts. A
virus may pick up gene of the host in place of its own gene
during its multiplication in the host cell.
•Such a virus is never virulent. It passes over the gene of the
previous host to the new host.
•Transducing viruses may carry the same genes (restricted
transduction) or different genes (generalized transduction) at
different times.