The document discusses microbial genetic recombinations, highlighting bacterial recombination methods such as conjugation, transduction, and transformation. It elaborates on the mechanics of each process, including the role of plasmids and transposons in gene transfer and genetic variability among microorganisms. Additionally, it outlines the discoveries and principles associated with each form of recombination, emphasizing their significance in microbial genetics.

1. MICROBIAL GENETIC RECOMBINATIONS
Dr. A. T. Sharma
Assist. Professor
Nanded Pharmacy College, Nanded

2. Introduction
• Micro-organisms have an ability to acquire genes and
undergo the process of recombination
• Bacterial recombination: DNA transfer from a donor
bacterium to a recipient bacterium
• Exchange of genetic material between two different
chromosomes of different organisms
• Principles of recombination applicable to prokaryotes
but not to eukaryotes
• Eukaryotes exhibit a complete sexual life cycle
• In microbes, three kinds of recombination occur-
- Conjugation
- Transduction
- Transformation

3. Conjugation
• A defined and programed process – sexual mode of
genetic transfer
• In bacterial conjugation, only a portion of chromosome
from donor to recipient cell
• Unidirectional transfer – separation of cells and
changes in genetic organization
• Retrotransfer: from recipient to donor cell
• Genetic exchange through a conjugation tube
• Process first postulated by Joshua Lederberg and
Edward Tatum (1946) in E. coli (Nobel prize in 1958)

4. F+ and F- Cross
• Genetic transfer through a plasmid (F- plasmid, fertility
factor) – F-positive/F-plus/F+ cell/male cell – Donor cell
• F-negative/F-minus/F- cell/female cell – Recipient cell
• Bridge formation between a donor cell and recipient cell
through plasmid
• Plasmid is not integrated with bacterial chromosome
• F-plasmid has two loci (tra and trb), an origin of replication
(OriR) and an origin of transfer (OriT)
• tra locus: Codes for proteins to form pili and and other
proteins necessary for attachment and transfer of F-
plasmid
• Trb locus: codes for proteins necessary for channel creation
for DNA transfer
• OriR: Site of replication
• OriT: Site at which enzyme relaxase/relaxosome cuts the
DNA strand of F-plasmid

5. Steps:
• Production and projection of pilus from donor
cell – begins contact with recipient cell
• A direct contact between donor and recipient
cell
• Enzyme relaxase cuts one of the two strands
of plasmid (T-strand)
• Replication of single strands in two cells
forming double stranded DNA – both cells
work as a donor cells

7. Hfr and F- Cross
• Hfr cell: A bacterial cell with F-plasmid integrated to its
chromosome
• F-plasmid together with bacterial chromosomal DNA forms
a rDNA called Hfr DNA
• During transfer, some portion of the donor DNA gets
transferred
Steps:
• Formation of sex pili for forming conjugation tube for cell to
cell contact
• Replication of Hfr DNA by rolling circle mechanism
• Breaking of circular Hfr DNA forming linear DNA
• Movement of a portion of F-plasmid to recipient cell
• Abrupt breaking of conjugation tube – only a part of Hfr
DNA transferred
• Transferred DNA integrate with recipient DNA – genetic
variability (Generally resultant cell is F- cell)

9. Transduction
• Genetic transfer through a non-replicating
bacteriophage (temperate phage)
• Discovered by Joshua Leaderberg and Nortor Zinder
(1952)
• A small bacterial DNA fragment incorporated in to an
attacking phage – infection to another bacteria, genetic
material transferred – genetic recombination
Types:
• Specialized transduction
• Generalized transduction

10. Specialized Transduction

11. Generalized Transduction

12. Transformation
• Genetic recombination in which DNA molecule of donor cell,
pass in to the recipient cell through the liquid medium.
• Transfer of cell-free or naked DNA
• Described by Frederick Grifith (1928)
• Transformation takes place by
- Spontaneous transformation (Natural) by DNA
uptake from environment
- Forced uptake in laboratory (Artificial)

13. Plasmids
• Term ‘Plasmid’ was first introduced by Joshua Lederberg (1952),
the American molecular biologist
• Plasmids are extra-chromosomal, self-replicating, double stranded
circular DNA molecules in a bacterial cell (it has its own origin of
replication)
Characteristics:
• Origin of replication
• Antibiotic resistance
• Metal/metalloid resistance
• Virulence determinants
• Bacteriocin production
• Biodegradative capabilities
• Symbiotic determinants
• Multiple cloning sites
• Promoter region
• Primer binding site

14. Applications of plasmids:
• Plasmids in gene therapy
• Plasmids in rDNA technology
Transposons (Transposable Elements – TEs)
• DNA sequences that are able to move from one
location to another in the genome
• Transposition (mobilization of TEs) was
discovered by Barbara McClintock during 1940
and 1950s
• Identified in all organisms, eukaryotes and
prokaryotes
• Play a role in genetic evolution

15. Types of Transposons
• Cut-and-Paste Transposons: They transpose
by excision (cutting) of the transposable
sequence from one position in the genome
and its insertion (pasting) to another position
within genome.

16. • Replicative Transposons: They transpose by a
mechanism which involves replication of
transposable sequence and this copy of DNA,
so formed, is inserted in to the target site
while the donor site remains unchanged.

17. • Retro Elements:
They transpose
through the process
of synthesis of DNA
from RNA by reverse
transcription and
insertion of DNA in
to the target DNA
site.

18. Significance
• Change the structural and functional
characteristics of genome
• Cause mutation
• Contribute in evolution
• Useful as cloning vector
• Searching and isolation of a particular gene

19. Thank you…!!!
(Disclaimer: The images and diagrams in this presentation
have been downloaded from the google source. I am grateful
to all the publishers & the google.)