The document presents an intricate overview of bacterial reproduction, distinguishing between vegetative, asexual, and a variant of sexual reproduction through genetic recombination methods such as conjugation, transformation, and transduction. It details various processes including binary fission, the formation of endospores, and the role of mobile DNA elements in genetic transfer among bacteria. The document also highlights landmark experiments in genetic transformation, notably those by Griffith and Avery, contributing significantly to microbiological genetic research.

1.  A Presentation by
 Dr. N. Sannigrahi,
 Associate Professor,
 Department of Botany,
 Nistarini college, Purulia
 ( NAAC Accredited ‘A” Grade)
 D.B. Road, Purulia (W.B)
 723101, India

3.  Unicellular organisms do not undergo reproduction like the multicellular
one and the story of the prokaryotes quite different from the rest neither in
mode nor in the complexity. Reproduction in bacteria is simply the
multiplication in number either by vegetative and asexual method. There is
no sexual reproduction neither by the formation of sex organ's followed by
the gametes nor by the fusion of the non-identical gamets.But in some
cases, objective of usual reproduction for the reassortment of the genes
takes place but this process is quite dissimilar from the rest. Mainly three
types of reproduction noted:
 Vegetative method-Only by the cell itself without any kind of
specialization
 Asexual method-Cell undergone modification by the dint of some
specialized structure to address the harsh environment
 Sexual method-this is not truly sexual one due to lack of desirable
specialization, rather it is the process of the recombination of genes in the
true sense.

4.  The vegetative method mostly executed by the decisive use of the body cell
followed by a certain degree of modification. It occurs by three methods-
 Budding,
 Fragmentation,
 Binary fission.
 BUDDING:
 a. small protuberance called bud at one end of the cell forms,
 b. Genome replication occurs and copy of the replicated genome enters into
the bud,
 c. The bud undergoes enlargement and finally the bud gets separated from
the parent cell
 d. The bud gives the formation of new cell.

5.  FRAGMENTATION
 During unfavorable condition, protoplasm undergoes compartmentalization
forming minute bodies called gonidia,
 Each gonidium now grows to a new bacterium under favorable condition,
 Prior to the formation of gonidium, genome undergoes replication to
increase the DNA content.
 BINARY FISSION
 The cell contents become doubled,
 DNA replication occurs , DNA undergoes partition and cross wall
formation takes place,
 Bacterial chromosome gets attached to the cell membrane and replicated
into two,
 The daughter DNA still attached to the cell wall and get separated by a
simple pinching off process,

7.  A cross wall is formed. The transverse plasma membrane is laid down
followed by the centripetal growth of the cell wall and splits the plasma
membrane into two halves.
 The good environmental condition favors this process and 20-30 minutes
are enough to multiply the cell,
 The binary fission enables the bacteria to multiply in geometric progression
to form a big bacterial colony within a short span.
 The large group of bacteria called Actinomycetes form branching hyphae;
spores develop , singly or chain , from the tips of these hyphae by
crosswall.If they enclosed in sac called sporangiospores and if not they are
called conidiophores. Very often, cyst, thick walled desiccation resistant
forms develop by the differentiation of vegetative cells and germinate
under suitable conditions as a part of reproduction.

8.  During unfavorable condition, the bacteria undergoes asexual process of
reproduction and this is enabled by the formation of endospore by the
following methods: A pert of the protoplast becomes concentrated around
the genome,
 A hard resistant wall is formed around it, the rest of the bacterial cell
undergoes degeneration,
 Each endospore is either spherical, or cylindrical or ellipsoidal in shape,
 Endospore is a resting spore undergoes a number of modification. The
outer layer is thin, delicate called –exosporium, followed by the spore coat.
Inner to spore coat, the cortex contains concentric rings of wall. Below the
cortex, the core cell wall is encircling the cell membrane and protoplasm,

10.  Under favorable condition, the endospore germinates by imbibing water,
activating the cytoplasm , synthesizing metabolites and swelling follows
the bursting of wall giving rise to the formation of new vegetative cell.
 The endospore consists of the bacterial DNA, ribosome and large
amounts of dipicolinic acid. Dipicolinic acid is a spore-specific chemical
that appears to help in the ability for endospores to maintain dormancy.
This chemical accounts for up to 10% -15% of the spore's dry weight. It
occurs in combination with large amounts of calcium and probably located
in the core i.e. in the central part of the spore. The calcium-DPA complex
possibly play a vital role in the heat resistance of endospores. Synthesis of
DPA and the uptake of calcium occurs during advance stages of
sporulation.

11.  Genetic recombination is a most dramatic episode in biological drama that
enables two genetic traits of two non-identical cells come together and
recombine in a manner and make the avenue of the formation of the 3rd cell
i.e. zygote to give the birth of new individual. It is one of the most
interesting biological process that acts expedite the biological evolution
process. The process of the genetic recombination in prokaryotes unlike
different from the eukaryotes. In bacteria, the sexual reproduction truly
absent but genetic recombination still prevails as a natural adaptation for
the new combination of genes. If the favorable new character is generated
by mutation, it spreads to the successors through this genetic
recombination. In bacteria, this process of mixing of genes take place
mostly by three methods-Conjugation, transformation & transduction.
 GENETIC RESHUFFLING: It enables the production of traits that differ
from the original parent,
 only the exogenote from the donor is transferred to recipient to enable
variation.

12.  Comparative genomic analysis of closely related microorganisms that
exhibit different phenotypes have revealed distinct genomic differences.
Often, these idiosyncratic differences result from horizontal gene transfer ,
the movement genes that are not direct descendents from one another.
These horizontal gene transfers allows cells to quickly acquire new
characters and drives metabolic diversity.
 Conjugation- transfer of genetic material occur through direct contact
between the two cells; donor and recipient
 Transformation- The exogenate(portion of the genetic complement of the
donor) is taken up by the recipient from the surrounding medium,
 Transduction- The transfer of a genetic materials occur from one cell to
other by bacteriophage or by a virus.

14.  The genome of the recipient is called endogenote and the incomplete
zygote is formed in this attribute is called partial diploid or merozygote.
 Transfer of free DNA released from a donor bacterium to recipient
bacterium through the liquid medium in which they grow,
 Does not require living bacteria cell, only requires DNA in the
environment,
 Transfer DNA regions from 1-10 kilo bases of DNA,
 A Kind of genetic transformation was discovered by F. Griffith (1928) on
the epoch making achievement. The experiment was conducted of the two
strains of Streptococcus pneumoniae (Pneumococcous pneumoniae) ; One
was virulent,(pathogenic) capsulated , smooth form(S) and other was
avirulent, non-pathogenic, non-virulent(non-pathogenic) rough(R).The
experiment designed as follows: Virulent strain(S) –injected into mice-mice
dead
 Avirulent strain® –injected into mice-mice lives
 Heat killed virulent(S)-injected into mice-mice lives
 Heat killed virulent (S) + living virulent ®-injected into mice-mice dead.
Isolated S type strain from the dead mice from the last experiment .

16.  The Virulent and avirulent characters were nothing but the presence of
gene present there after.
 The virulent strain responsible for the death of the mice but when it was
heated and injected, the effect of the gene did not produce any outcome.
 But when the heat killed virulent strain treated with living avirulent, the
transformation of the avirulent to virulent one takes that caused the death
of the mice.
 Initially, Griffith thought the virulence due to the polysaccharide present in
the capsule but later on, the experiment conducted by O. T. Avery, Mac
Leod & Mc Carty (1944) confirmed the transforming principle was none
but DNA, not polysaccharide present in the capsule. Thus research open a
new novel avenue of genetic research in the microbiological field.
 Heat treated S+R=Mice death, Death mice- S type + R-type (Isolated
bacteria)
 Dnase + heat treated S+R= Alive
 Protease + heat treated S+ R= Death

18.  Competence is the process that enables the cell to incorporate the foreign
DNA,
 The donor DNA binds to the cell surface by the DNA binding protein inside the
recipient cell,
 Either dsDNA or ssDNA enters into the recipient cell,
 The endonuclease enzyme degrades one of the strand and allows the
incorporation, ligase enzyme filled up the gap,
 All bacteria in the medium containing donor DNA( exogenote) are not capable
of transformation, only the competent can have the pleasure of this
transformation. But the ability of transformation can be induced by certain
methods. On the basis of the ability of transformation, it can be divided into
two types
 Natural transformation-Bacteria encoded with the competency factor in their
genome like mostly Gram(+) bacteria like S.pneumoniae, Bacillus subtilis etc,
 Artificial Transformation-The artificial transformation can be induced in the
non-competent bacteria by the addition of cations like Ca or Rubidium chloride
or electroporation by heat shock in the medium like most Gram(-) negative
bacteria, Azetobacter agilus etc.

19.  A kind of genetic transformation by which two sexually differentiated
bacterial cells –donor and recipient have the pleasure of it. A considerable
segment of donor genetic material is transferred to the recipient cells
which may undergo recombination with the corresponding (homologous)
segments of the recipient genetic materials. The segments of DNA may be
larger one in comparison to the other two methods of recombination.
According to Hayes( 1952), conjugation is a heterothallic system in which
recombination is mediated by one way transfer of genetic material from the
donor to recipient bacterial cell through the conjugation tube Let us explore
the beauty of this drama under two headings
 Donor and Sex factor,
 Process of conjugation & Sexduction.

20.  Donor state is attributed by the presence of gene and it might be infectious
vector ( Hayes, 1953) in the donor cells. It is termed as Conjugons ( Luria,
1963) and conjugans termed as episomes.Episomes are cytoplasmic DNA
elements having capacity to integrate with the bacterial chromosome.
Donor state is called fertility factor or F factor like other factors Rtf, col
etc. When a bacterium contains F factor called F+ as male and the recipient
as F (-).F+ and Hfr are basically but the later can transfer large segments of
genome. Both F + and Hfr are characterized by the presence of flagellum
like structure on the cell surface called sex pilus. The sex factors perform
the following functions:
 Determine the donor state, Help in the synthesis of surface antigen,
Mobilize the genetic material transfer
 Provide enenergy during the process

21.  F+ and F- Conjugation
 This is the most normal when the F factor is transferred but not the
bacterial genome,
 It converts the recipients to F+,
 The circular dsDNA of the F factor is nicked on one of the strand,
 The strand passes as a single strand into the recipient cell and synthesize
the complementary strand and circularizes into the recipient cell,
 The donor dsDNA also regain the normal sate by following using
replication pattern,
 The nick is made at the site called Ori T (origin of transfer) and the
replication occurs by rolling circle mechanisms.

22.  Hfr and F- conjugation
 Hfr is a strain where the F factor is integrated with the bacterial
chromosome. This integration is due to crossing over between the regions
of homology of shared by the plasmids and the bacterial genome. The
homologous sequence of DNA in the bacterial chromosome are called
insertion sequences.
 When the Hfr strain comes in contact with F- strain, replication transfer
begins with F plasmid region at Ori T site and continues into the
chromosomal regions of the bacterial genome.
 The transfer starts from the cut region and the bacterial DNA is transferred
through the conjugation tube keeping the F factor at its rear end,
 If the entire DNA along with F factor is transferred , it becomes Hfr but
only bacterial genome transfers, it become F-

24.  The specific pairing occurs by the specific flagellum called sex pilus
present in both Hfr and F- cells which has a hole of 2.5µm diameter
through which the transfer of genetic material transfer takes place.
Recombination occurs only at homologous points
 Specific pairing of the two strains are desired
 Transfer of genetic material from donor to recipient,
 Genetic recombination between donor and recipient cell,
 Expression of new phenotype in the recipient cell is obligatory.
 Transfer of plasmid DNA is efficient and rapid; under favorable conditions
virtually every recipient cells pairs with a donor acquires a plasmid.
Transfer of F plasmid having 100Kbp of DNA takes about 5 minutes.

25.  It is a kind of conjugation between F`(Prime) and F- cells,
 The male bacteria called F`, and F` cells have F factor with some genes of
the bacterial genome in it,
 F` cells originate from Hfr strain. We know that Hfr is formed by the
integration with bacterial chromosome. But at times of integration reverts
during which the F factor brings some portion of the bacterial genome in
exchange of its own or even not. Thus the F factor has some genes of the
bacterial chromosome and becomes F`,
 During conjugation between F` and F- cells, the F` factor is transferred to
the recipient F- cells. The recipient cell becomes a heterozygous for the
portion of genes present in the F` factor. Genetic recombination takes
place. The genetic recombination mediated by F` factor called sexduction
as identified by Adelberg and Burns (1956).

26.  An unique type of genetic recombination where genes of one bacteria
transferred to another by means of bacteriophages, a vector. The virus of the
bacteriophage have the excitement of the transfer is called transducing phage.
 This unique type of gene transfer was discovered by Zinder and Lederberg
(1952) on Salmonella typhimurium.
 The overall process is as followed: Here, the bacteriophage acquires a portion
of bacterial DNA of the host cell where it reproduces and transfer it to the
another bacterial cell which it infects. Such phage is called transducing phage.
 It is mediated by lambda phage that experiences Lysogenic type of life cycle,
 The virus injects its nucleic acid into the host cell and the viral genomes
undergone integration with the bacterial genome and remain prophage for a
period of time during which it multiplies along with the reproduction of the
bacteria,
 Delysogenisation occurs and viral genome detaches from the bacterial genome
to enter the lytic phase,
 Viral genomes brings some bacterial genome may or may not exchange.

28.  The viral genome with some bacterial genes now included in new progeny
viruses which are released after lysis of the bacterial cell,
 These bacteriophages with bacterial genes infect new bacterial cells in the
same manner and their genome gets integrated with the new host genome
and the genetic recombination occurs,
 The second bacterial cells express some characters of the previous bacterial
cell by the courtesy of the virus, bacteriophage (lambda).
 On the basis of the gene transfer as mediated bacteriophage, transduction
mainly of two types-
 Generalized Transduction- Here the Lytic cycle is followed during
transduction.
 Here, the bacterial DNA is disintegrated and the Lytic cycle is followed as
principle.
 The virus instead of it own synthesized DNA, it collects bacterial DNA and
introduced to the another bacterial cell by Lytic process and integrates with
the new bacterial cell.

29.  Specialized Transduction: This kind of genetic recombination is done by
the active participation of lysogeny cycle.
 Here, the phage DNA is integrated with the bacterial DNA-called
prophage.
 It attached with the bacterial until it becomes stable,
 After unstable condition, it becomes get separated from the bacterial DNA ,
get separated from the host bacterial DNA along with its some of the
fragments of bacterial DNA,
 Let, the viral genome collects ‘gal’ gene from the bacteria and inserted into
the another bacterial cell, insert the ‘gal’ gene into the second bacteria,
 Now, the 2nd bacteria contains two ‘gal’ gene and get inserted into the
 bacterial DNA. Now the new bacteria contains two ‘gal’ genes along with
the preexisting ‘bio’ gene.
 As a result, the bacteria has been genetically modified by the virus via
transduction.

31.  When the lysate contains lower portion of ƛ dg it is called by LFT(Lower
Frequency of Transducing).When high proportion or all progeny
bacteriophages are ƛ dg, the lysate is called HFT (High Frequency of
Transducing).
 Mobile DNA elements refers to discrete segments of DNA that moving as
units from one location to other within other DNA molecules. Most mobile
DNA elements that consists of transposable elements and the process by
this DNA movement takes place is called transposition. Two types of
transposable elements in Bacteria are Insertion sequences (IS) and
Transposons.They carry genes encoding transposase, the enzyme necessary
for transposition. These are two methods of the recombination in bacteria
are also fund beside the traditional genetic recombination found to occur in
this domain.

32.  ACKNOWLEDGEMENT
 Google for different images,
 Different websites for content,
 Introduction to Microbiology- Pelzer, Chan and Krieg,
 Brook Biology of Microorganisms,
 Microbiology & Phycology- Dash & Mishra,
 A textbook of Microbiology- Dubey & Maheswari.
 Disclaimer:
 The content writer conveys thanks and acknowledges help from the following to
develop this article. This has been designed for online resources without any
financial interest.