Transcript microbiology

Shatha Khalil Ismael
Transformation
The uptake of DNA from one bacterial
cell, either as a plasmid or a fragment,
by another cell is called transformation
it Is a process by which free DNA is
incorporated into a recipient cell and
bring about a genetic change..
Certain species of Gram- negative, grampositive bacteria and some species of
Archaea are transformable .
Since the DNA of procaryote is
present in the cell as a large single
molecule, when the cell is gently
lysed, the DNA pours out, and
because its extreme length
bacterial chromosome breaks
easily.
Mechanism of transformation in gram
positive bacterium :
• Binding of double
stranded DNA by a
membrane bound
DNA binding
proteins
• Passage of one of the
two strands into the
cell while neuclease
activity degrades the
other strand
• The single strand in
the cell is bound by a
specific proteins and
recombination with
homologous regions
of the bacterial
chromosome is
mediated by RecA
protein
• Transformed cell
Video transformation
The end product of bacterial
transformation?
DNA is degraded by the host cell
 integration of the DNA by nonreciprocal
recombination
 Plasmid is stably transformed into the cell
but separate from the chromosome

Bacterial conjugation:
Process of genetic transfer that involves cell-to-cell
contact.
A pilus is a hairlike appendage found on the
surface of many bacteria.
The terms pilus for the appendage required
for bacterial conjugation
Video conjugation
DNA transfer during
conjugation:
DNA synthesis is necessary for DNA transfer
to occur during conjugation a bacteriophages,
called rolling circle replication ,, explains
DNA transfer during conjugation
Rolling circle replication describes a
process of unidirectional nucleic acid
replication that can rapidly synthesize
multiple copies of circular molecules
of DNA or RNA, such as plasmid, the
genome of bacteriophages, and the circular
RNA genome of viroids . Some eukaryotic
viruses also replicate their DNA via a rolling
circle mechanism.
Video rolling
the formation of Hfr strains and
chromosome mobilization
The F plasmid of E-coli can under circumstance,
mobilize the chromosome for transfer during
cell-to-cell contact.
When the F plasmid is integrated into the
chromosome , the chromosome becomes
mobilized and can lead to transfer of
chromosomal genes
Cells possessing an unintegrated F plasmid
are called : F +
those that have a chromosomeintegrated F plasmid are called
Hfr
(high frequency of recombination )
Both F+ and Hfr cells are donors and are
unable to take up a second copy of the
Fplasmid or genetically related plasmid
The conjugation between an f – and an Hfr
donor lead to transfer of genes from the host
chromosome because the plasmid is part of
the chromosome
The F- recipient cell may express a
new phenotype.
Plasmid integration is a mechanism
for mobilizing the cells main
genetic resources
The presence of F plasmid results in 3
distinct alternations in the properties of a
cell:
1- the ability of synthesize the F pilus
2- the mobilization of DNA for transfer to
another cell
3- the alternation of surface receptors
 So the cell is no longer able to behave
as a recipient in conjugation.
Transduction :
In transduction DNA is transferd from cell
to cell by a bacterial virus ( bacteriophage ).
Genetic transfer of host genes by viruses
can occur by :
1- generalized transduction
2- specialized transduction
generalized transduction
Most DNA derived from virtually
any portion of the host genome
becomes a part of DNA of the
mature virion in place of the viral
genome
Note that the “normal” versions contain phage
genes while “a transducing particle” contains
host genes .
Video general
specialized transduction
Occur only in some temperate viruses .
DNA from a specific region of the host
chromosome is integrated directly into
the virus genome , usually replacing some of
the virus genes.
The transducing virion in BOTH generalized
and specialized transduction is usually no
infective as a virus because bacterial genes have
replaced some or all necessary viral genes.
Video specialized
Thank you 
A mechanism of horizontal gene
transfer (HGT)
in Bacteria and Archaea?
Conjugation, Transformation ,Transduction
What is the role of the genes related
to the F factor in conjugation
1. Aid in DNA transfer,,
2. Forms sex pili,,
3. Includes IS elements that assist plasmid
integration into the host cell's chromosome,,
Which of the following is TRUE of
conjugation?
1.
2.
3.
Requires physical contact between microbes
Unidirectional
Involves plasmids
Conjugation in which the donor transfers
chromosomal genes with great efficiency but
does not change the recipient into F+ cells is
known as??
HFr conjugation
What happens to donor DNA when
it enters the recipient cell



Integration of the DNA into the recipient's
chromosome
Replicates separately from the host DNA in a
plasmid
Donor DNA remains in the cytoplasm, unable to
replicate
A reciprocal exchange between a pair of
DNA molecules with the same
nucleotide sequence is called
Homologous recombination
insertion sequences of transposable
elements..
It contains only the gene for the enzyme
transposase
replicative transposition,,
Contains genes coding for transposase
and resolvase
the role of the genes
related to the F factor in
conjugation
1. Aid in DNA transfer,,
2. Forms sex pili,,
3. Includes IS elements that assist plasmid
integration into the host cell's chromosome,,
Conjugation in which the donor
transfers chromosomal genes
with great efficiency but does
not change the recipient into
F+ cells is known as
HFr conjugation