This document discusses plasmids and transposons in bacteria. It explains that plasmids are small, circular pieces of DNA separate from the bacterial chromosome that can contain genes enhancing survival. Plasmids can transfer genes horizontally through conjugation. Transposons are mobile DNA elements that can move locations within a genome, sometimes carrying antibiotic resistance genes. They include insertion sequences and larger transposons, which may contain resistance genes flanked by insertion sequences that allow for transposition. Together, plasmids and transposons facilitate horizontal gene transfer and generation of genetic diversity in bacteria.

1. Microbial genetics
Bio 433
By
Dr. Mona Othman Albureikan

2. • Plasmids are extra
chromosomal rings of DNA
found in some bacterial cells.
• These are considerably
smaller than the bacterial
chromosome, ranging in size
from a few thousand to several
million bp.
Plasmids

3. • Though plasmids are
necessary for the daily life
of the cell, they often
contain genetic information
that can enhance the
microbe's ability to survive
and pass it genetic
structure to others.
Plasmids

4. Plasmids
• Plasmids are genetic elements
that can also provides a
mechanism for genetic
change.
• Plasmids are small, circular
pieces of DNA that exist and
replicate separately from the
bacterial chromosome.

5. • Plasmids are sometimes referred
to as factors, based on the type of
genetic information they contain:
• Fertility (F) factors are plasmids
that carry genes necessary for a
cell to transfer DNA to another
compatible cell through a process
called conjugation.
Plasmids

6. • Resistance (R) factors carry genes that
allow a cell to be resistant to antibiotics
or other antimicrobial compounds.
• R plasmid usually has two types of genes:
• R-determinant: resistance genes that
code for enzymes that inactivate certain
drugs
• RTF (Resistance Transfer Factor): genes
for plasmid replication and conjugation.
Plasmids

7. • Without resistance genes for a
particular antibiotic, a bacterium is
sensitive to that antibiotic and
probably destroyed by it.
• But the presence of resistance genes,
on the other hand, allows for their
transcription and translation into
enzymes that make the drug inactive.
Plasmids

8. • Resistance is a serious problem. The widespread use of antibiotics in
medicine and agriculture has lead to an increasing number of
resistant strain pathogens.
• These bacteria survive in the presence of the antibiotic and pass the
resistance genes on to future generations.
• R plasmids can also be transferred by conjugation from one bacterial
cell to another, further increasing numbers in the resistant population.
Plasmids

9. • Bacteriocidin factors carry genes
for the production of toxins that
kill other bacteria that might
compete with the cell for
nutrients and space.
• Virulence plasmids carry genes
that enable a nonpathogenic
bacterium to become a pathogen.
Plasmids

10. Transposons
• Transposons (Transposable
Genetic Elements ,TE ) are
pieces or some genes of
DNA that can move from one
location on the chromosome
to another, from plasmid to
chromosome or from one
plasmid to another.

11. • The American geneticist Barbara
McClintock discovered it through her
study of the genetic of corn in the 1940.
• She called these segments of
DNA transposable genetic
elements (transposons) or, more
commonly, "jumping genes."
• McClintock won the Nobel Prize for her
discovery.
Transposons

12. • The first transposable element is
discovered in bacteria is called
insertion sequences or IS elements.
• The Transposons may
cause mutations.
• They also, may increase (or
decrease) the amount of DNA in
the genome of the cell.
Transposons

13. Two methods of
transposition

14. Types of
Transposable
Elements:
• Transposable
elements are of two
main types:
1. Insertion sequences
(Is) or Simple
Transposons.
2. Transposons (Tn) or
Complex Transposons.

15. 1. Insertion sequences (Is)
• Insertion sequences (Simple Transposons) are short DNA of about
800-1400 bp, and have the ability to transpose.
• An insertion sequence contains only one gene that codes for
transposase, the enzyme that catalyzes transposition.

16. • The transposase gene is flanked
by two DNA sequences called
inverted repeats because that two
regions are upside-down and
backward to each other.
• Transposase binds to these
regions and cuts DNA to remove
the gene.
1. Insertion sequences (Is)

17. • There are different insertion sequences such as IS1, IS2, IS3, IS4 and so on in
E. coli.
• Recently IS21 has been reported in bacteria by Willetts etal., (1981). IS
elements have 9-40 bp inverse repeats (so that a particular IS elements have a
similar sequence of bases at each ends but in reverse order) at their two ends.
1. Insertion sequences (Is)

18. • They also promote recombination between non-homologous
chromosomes and are considered to be involved in the integration of
episomes into bacterial chromosomes.
• IS elements codes for only those proteins which are needed for their
transposition. For example IS1 has two genes which code for the
proteins InsA and InsB which are needed for its transposition. Other
IS elements contain only a single long coding region which codes for
the transposase which sponsors their transposition.
1. Insertion sequences (Is)

19. • IS elements occur at many sites in the E. coli chromosome but their
distribution is non-random; they seem to be integrated at certain sites.
• Integration of an IS
element in a gene
destroys its function.
• IS elements are believed to be responsible of spontaneous gene
mutations in bacteria and bacteriophages.
1. Insertion sequences (Is)

20. • Transposons (Tn) (Complex
Transposons) are more complex
transposable elements.
• They are usually more than 2000 bp
long, carry one or more genes unrelated
to their transposability (e.g., genes for
antibiotic resistance), and have IS-like
elements repeated at their ends.
2. Transposons (Tn)

21. • The IS elements at the two ends of a Tn element may be either in the same orien-
tation (direct terminal repeats) e.g., IS1 at the ends of Tn 9 of E. coli, or in the
opposite orientation (inverse terminal repeats) e.g. IS10 in Tn 10 of E. coli.
2. Transposons (Tn)

22. • Transposable elements are
found in eukaryotes, e.g.,
Maize, yeast, Drosophila,
etc. and the DNA genomes
of certain cancer-causing
viruses (retroviruses) are
similar in structure to
bacterial Tn elements.
2. Transposons (Tn)

23. • It consist of one or more genes between two insertion sequences.
• The gene, coding for antibiotic resistance, for example, is carried along
with the transposon as it inserts elsewhere.
• It could insert in a plasmid and passed on to other bacteria by conjugation.
2. Transposons (Tn)

25. Episome
• A genetic element in bacteria that can replicate free in the cytoplasm
(has a different number of copies) or can be inserted into the main
bacterial chromosome and replicate with the chromosome.
• Plasmids are an example.
• An episome is distinguished from other pieces of extra chromosomal
DNA, such as plasmids, on the basis of their size.
• Episomes are large, having a molecular weight of at least 62 kilobases.

26. References
 Molecular Genetics of Bacteria ( 4th Edition ) (2013), Larry Snyder , Joseph E. Peters , Tina M. Henkin , Wendy
Champness ISBN 10: 1555816274 ISBN 13: 9781555816278.
 Molecular Genetics of Bacteria, 5th Edition, by Jeremy W. Dale, Simon F. Park ,April 2010, ©2010.
 Genetics of Bacteria, Sheela Srivastava,(2013) ISBN: 978-81-322-1089-4
 Microbial Genetics. (1994). Jones and Bartlett Series in Biology. Jones and Bartlett Publishers, Inc.; 2nd
edition, ISBN-10: 0867202483, ISBN-13: 978-0867202489, 484 pages.
 Microbial genetics. (2008). Jones and Bartlett series in biology
Series of books in biology. David Freifelder, publisher, Jones and Bartlett, 1987. 601 pages.
 Molecular Biology: Genes to Proteins Hardcover . (2007). Burton E. Tropp, Publisher: Jones & Bartlett Publishers; 3
edition, ISBN-10: 0763709166, ISBN-13: 978-0763709167, 1000 pages .