The document discusses plasmids, which are circular, double-stranded DNA molecules that exist independently of bacterial chromosomes and can carry genes important for functions like antibiotic resistance and gene transfer. It details various types of plasmids, such as conjugative and non-conjugative, their roles in bacterial conjugation, and specific examples like F-plasmids and R-plasmids, highlighting their importance in genetic exchange and antibiotic resistance. It also covers the structural features, functions, and implications of plasmids in microbiology.

1. PLASMIDS
Submitted to Submitted by
Dr. Aghil soorya Krishnapriya M
Department of Botany Roll no: 10
St.Teresas college 1st Msc Botany

2. JOSHUA LEDERBERG
 The term ‘plasmid’ was
first introduced by the
American molecular
Biologist Joshua Lederberg
In 1952.
 Known for his work in
o Genetics
o Artificial intelligence
o Space exploration
 Won Nobel prize in Physiology or Medicine for discovering that
bacteria can mate and exchange genes.

3. WHAT IS PLASMID
• Plasmids are circular, double-stranded DNA molecules that
exist independently of host chromosomes.
• Present in many bacteria and also found in yeasts.
• Have their own replication origins and are autonomously
replicating and stably inherited.
• A replicon is a DNA molecule or sequence that has a
replication origin and is capable of being replicated.
• Plasmids and bacterial chromosomes are separate replicons.
• Plasmids have relatively few genes, generally less than 30.

4. Plasmid cont…
• Their genetic information is not essential to the host and
bacteria that lack them usually function normally.
• They are extra chromosomal DNA molecule.
• Plasmid DNA may sometimes be integrated with chromosomal
DNA of bacteria.
• Such integrated forms are called ‘episomes’.
• They can carry genes for toxins and proteins that promote
transfer of plasmid to other bacterial cells.
• Size of plasmid varies from less than 1.0kb to more than
200kb.
• Smaller plasmids are much desirable for gene cloning
experiments.
• Larger plasmids are less in number whereas smaller ones are
more.

6. TYPES OF PLASMIDS
Based on function:
PLASMIDS
CONJUGATIVE NON-CONJUGATIVE

7. Types of plasmid cont…
CONJUGATIVE PLASMIDS
 Plasmids are transferred from bacterium to bacterium (usually
members of same species or very closely related species)
through conjugation.
 To this group belong R plasmid, F plasmid and certain
bacteriocinogen plasmids.
 Conjugative plasmids are common in Gram-negative bacilli.
 They are relatively large-approximately 250kb in size.
 Large plasmids are usually present at 1-2 copies per bacterium.
 The replication of these plasmids are closely linked to that of
bacterial chromosome.

8. Types of plasmid cont…
NON-CONJUGATIVE PLASMIDS
 Common in Gram-positive bacteria.
 But also seen in some gram-positive organisms.
 Usually small, 1-10kb in size.
 Multiple copies may be present in each bacterium.
 They can also transferred to another cell when the same
bacterium carries both conjugative and non-conjugative
plasmids.
 Once conjugation is established, the donor can transfer non-
conjugative plasmids.

9. CONJUGATION?
• It is a process by which a ‘male’ or ‘donor’ bacterium mates or
make physical contact with a ‘female’ or ‘recipient’ bacterium
and transfer genetic elements.
• In conjugation, genetic exchange between bacteria requires
direct cell to cell contact during mating of bacteria.
• Bacterial conjugation in E. coli was discovered by Lederberg
and Tatum in 1946, when they observed sex-like exchange
between two mutant strains of E.coli called k12.
• Conjugation results in the one-way transfer of DNA from a
donor cell to a recipient cell through sex pilus.

10. Conjugation cont…
• Only bacteria that contain F plasmid can act as donors, while
bacteria lacking F act as recipients.
• Conjugation involves two cell types: donors as F+ male cells,
which possess F factor and recipients are called F- cells as
they lack F factor.
• Once F factor is passed from F+ cell to F- cell, the recipient
cell becomes F+ and is able to pass fertility factor to another
F- cell.

12. F-FACTOR
• The fertility factor possess genetic information required for
synthesis of sex pilus and for self transfer.
• It do not contain other identifiable genetic markers such as
drug resistance.
• When plasmid containing F factor becomes integrated into
bacterial chromosome, cells are known as Hfr cells.
• Hfr cells are high frequency recombinant strains of cells
because such cells are able to transfer chromosomal genes to
recipient cells at high frequency.
• The mating between Hfr cells and F- cells results in transfer of
part of F genome plus some host cell genes from donor cell.

13. F factor cont…
• The recipient F- cells usually remain F- after conjugation.
• Because only part of F plasmid from donor Hfr cell to
recipient cell has been transferred by conjugative process.
• Thus recipient cell does not turn into Hfr and is unable to serve
as a conjugation does.

14. STRUCTURE
The most common functional segments constituting F factors are:
 OriT (Origin of Transfer): The sequence which marks starting
point of conjugative transfer.
 OriV (Origin of Vegetative Replication): The sequence starting
with which plasmid DNA will be replicated in the recipient
cell.
 tra-region : Genes coding the F pilus and DNA transfer
process.
 IS (Insertion Elements): Composed of one copy of IS2, two
copies of IS3 and one copy of IS1000; so called ‘selfish
genes’.

16. FUNCTIONS
• The F- factor allows donor to produce a thin, tubelike structure
called a pilus, which the donor uses to contact the recipient.
• The pilus then draws the two bacteria together, at which donor
bacterium transfer genetic material to the recipient.
• It control sexual functions of bacteria with a fertility inhibition
system.

17. R-PLASMID
• Also known as Resistance plasmid.
• This plasmid is of great medical significance.
• First reported by Japanese investigators in 1959 who observed
that there was sudden rise in incidence of infections caused by
Shigella strains which cause epidemic of dysentry.
• They are also found in faeces of patients.
• The shigella strains are resistant simultaneously to multiple
drugs; sulphonamides, streptomycin, chloramphenicol and
tetracycline.
• These patients also showed E.coli in their faeces which are
resistant to same drug.

18. R-Plasmid cont…
• This plasmid has two components:
-resistance transfer factor(RTF)
-resistance determinant(r)
 RTF carries genes responsible for conjugational transfer and
replication.
 R for each of the several drugs and some of them replicate
simultaneously.
 The entire plasmid (RTF+r) =R Factor.
 R factor contain several r determinants and resistance to eight
or more drugs can be transferred by conjugation
simultaneously.
 When two bacteria (one containing R plasmid and other
devoid of R) conjugate, the R plasmid is transferred to later
that lacks R plasmid.

19. STRUCTURE
• The structure of R plasmid is a circular piece of DNA.
• Length range between 80-95 kb.
• Constitute major portion of R-RTF molecules.
• This plasmid is largely homologous to F factor and contain
similar genes.
• Contain fin 0 gene-repress function of transfer operon.
• R factor vary in size and in content of genes for drug
resistance.
• R determinant is smaller than RTF.
• Both RTF and R determinant combine to form one unit.
• They are separated from each other by one IS 1 element on
either side.
• IS 1 help in exchange of R determinant between different type
of R-RTF units.

21. FUNCTIONS
• Important role in transmission of MDR genes in bacteria.
• Involved in gene carrier for autonomous replication,
conjugation and resistance to ampicillin.
• Contain genes that can build resistance against antibiotics.
• Helps bacteria in producing pilli.

22. DIFFERENCE BETWEEN F AND R-PLASMID
F PLASMID
• Has fertility factor necessary
for conjugation.
• Has F or fertility factor.
• Can form sex pilus and can
transfer genetic materials
through conjugation.
 When conjugation happens
between F+ and F – cells,the
resultant is two F+ cells.
 Also, the spread of F+ cells
is not a big threat.
R PLASMID
• Has antibiotic resistance
gene or resistance factor.
• Has R or resistance factor.
• Cannot form sex pilus. But,
a bacterium with an F factor
can pump the resistance
gene to another bacterium.
• When R factor is
transferred, it creates
antibiotic resistance in
bacteria.
• Thus, spread of R factor is a
threat to antibiotic
treatments.

23. COL PLASMID
• Also known as Colicinogenic factor.
• Found in several species of coliforms which produce
extracellular colicins.
• These antibiotic like bactericidal substances are lethal toxins
for other strains of same or closely related species of bacteria.
• Since similar antibacterial substances are also produced by
bacteria other than coliforms, this group of substances are
called bacteriocins.
• Colicins are produced by E.coli.
• Bacterial strains producing bacteriocin help interspecies typing
of organisms.

24. Col plasmid cont…
• Production of colicin is determined by a plasmid known as Col
factor.
• Resembles F factor in promoting conjugation.
• It also possess genetic information for self-transfer and at
times, transfer of chromosomal elements.

25. STRUCTURE
• It is a small, closed circular plasmids.
• The length of Col plasmid is 6646bp.
• It lacks mob gene( mobility genes) and bom sequence(basis of
mobility).
• It cannot complete the transmission independently.
• It contains gene colicin E1, which produce bacteriocin.
• It also codes for immunity against bacteriocin with imm gene.

27. FUNCTIONS
• It contain genes that make bacteriocin, also known as coliocin.
• Coliocins are proteins that kill other bacteria and thus defend
host bacterium.
• Bacteriocins are found in many types of bacteria including
E.coli, which gets them from plasmid ColE1.

28. REFERENCES
1. Dubey, R.C.(1999). A textbook of microbiology. S.Chand and
company pvt.ltd.
2. Purohit, S.S.(2014). Microbiology fundamentals and
applications. Student edition.

29. THANK YOU