bacterial reproduction

1. Bacterial Reproduction
Dr. Thirunahari Ugandhar
Head & Assistant Professor in Botany

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Introduction
Bacteria can reproduce in one of two ways:
1. Asexually
2. Sexually

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4. Asexual Reproduction
 The following points highlight the five
methods by which reproduction in bacteria
takes place. The methods are: 1. Binary
Fission 2. Conidia 3. Budding 4. Cysts 5.
Endospore.
 Method # 1. Binary Fission:
 In binary fission, single cell divides into two equal
cells. Initially the bacterial cell reaches a critical
mass in its structure and cellular constituents.
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Asexual Reproduction
Binary Fission:
 one parent involved
 offspring are identical to parent & each other
Advantages:
1. simple: only 1 parent
2. offspring are fully formed (no maturation needed)
3. very fast (20 min. in ideal conditions)
 after 24 hrs:
1 bacterium 2x106 kg of cells
(enough to cover the earth)

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7. Asexual Reproduction
Disadvantages:
• no genetic variety
• one unfavourable environmental condition can wipe out
whole population
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Asexual Reproduction
Binary Fission:

9.  Method # 2. Conidia:
 Conidia formation takes place in filamentous
bacteria like Streptomyces etc., by the formation
of a transverse septum at the apex of the
filament.
 The part of this filament which bears conidia is
called conidiophore. After detachment from the
mother and getting contact with suitable
substratum, the conidium germinates and gives
rise to new mycelium.
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11.  Method # 3. Budding:
 The bacterial cell develops small swelling at one
side which gradually increases in size.
 Simultaneously the nucleus undergoes division,
where one remains with the mother and other one
with some cytoplasm goes to the swelling.
 This outgrowth is the bud, which gets separated
from the mother by partition wall, e.g.,
Hyphomicrobium vulgare, Rhodomicrobium
vannielia, etc.
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12.  Method # 4. Cysts:
 Cysts are formed by the deposition of
additional layer around the mother wall.
These are the resting structure and during
favourable condition they again behave as
the mother, e.g., many members of
Azotobacter.
 Method # 5. Endospore: Spores are formed
during unfavourable environmental condition
like desiccation and starvation. As the spores
are formed within the cell, they are called
endospores. Only one spore is formed in a
bacterial cell. On germination, it gives rise to
a bacterial cell.
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13. Sexual Reproduction
 The following points highlight the three methods
of Sexual Reproduction (Para Sexuality) in
Bacteria. The methods are: 1. Conjugation 2.
Transformation 3. Transduction.
 Method # 1. Conjugation:
 It was first discovered in Escherichia coli by
Lederberg and Tatum (1946). They found that
two different types of auxotroph (nutritional
mutants) grown together on minimal medium
produced an occasional prototroph (wild type).
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16. Bacteria Transformation
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Sexual Reproduction
 two parents involved
 offspring are genetically different
to parents & to each other
Advantages:
 genetic variety i.e. some are able to adapt to
unfavourable conditions (ex: antibiotic resistance)
Disadvantages:
1.more complex: slower because must find a
compatible partner
2.no new individuals produced
(i.e. no increase in population)

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21. Bacterial Conjugation
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• plasmid copies itself
• passes through pili
(cytoplasmic bridge) into
recipient cell
• cells separate with both
cells containing the
plasmid
plasmid
donor recipient
cell (+) cell ( - )
pili

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23. Bacterial Conjugation
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30. Method # 2. 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.
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33. Method # 3. Transduction
 It is the transfer of foreign genes by means of
viruses.
 Transduction was first discovered by Zinder and
his teacher Lederberg (1952) in Salmonella
typhimurium.
 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.
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