Chapter 3
BACTERIAL GENETICS
Learning outcome:
By the end of this chapter, students should be able to;
1) Describes the mechanism of gene expression along with various elements controlling the
same in bacteria.
2) Discus mechanisms of genetic recombination in bacteria.
3) Explain the different mode of genetic recombination i.e. transformation, conjugation and
transduction.
4) Explain the involvement of bacteria in genetic manipulation of our food.
3.1 Introduction
Genetics is the study of heredity and variations. Genetic variation is the key to the survival of a
species, allowing a species to adapt to changes in their environment by natural selection. That's
true for bacteria as well. Like other living organisms, bacteria also multiply and pass on their
characteristics from generation to generation. There are also the possibilities of variations in a
small proportion in the inherited characters of their progeny.
Bacteria reproduce by binary fission. As a result of binary fission, bacteria produce clones or
genetically identical copies of the parent bacterium. Since the offspring bacteria are genetically
identical to the parent, binary fission doesn't provide an opportunity for genetic recombination or
genetic diversity (apart from the occasional random mutation) in bacteria. The three other
mechanisms responsible for transfer of genetic materials take place in bacteria. These are termed:
as transformation, conjugation and transduction.
3.2 Genetic recombination in bacteria
Bacteria can transfer genes from one strain to another by three different mechanisms:
transformation, conjugation and transduction, these events clearly show the universality of
sexuality in the living world. The genetic recombination in bacteria has a very vital significance.
Some of them are as follow:
Transfer of antibiotic resistance genes: The remarkable spread of resistance to multiple
antibiotics may have been aided by the transfer of resistance genes within populations
and among species.
, As a tool to study advances of molecular biology and biotechnology: Many bacteria
have enzymes that enable them to destroy foreign DNA that gets into their cells. It seems
unlikely that these would be needed if that did not occur in nature. In addition, the prime
enzymes of bacterial reproduction namely restriction endonucleases have provided the
tools of molecular biology. Most of the advances in biotechnology industry directly
depend on the use of these enzymes.
Study of Evolution: The recent completion of the sequence of the entire genome of a
variety of bacteria (and archaea) suggests that in the past the genes have moved from one
species to another by horizontal gene transfer.
3.3 Transfer of genetic material
Whenever two fragments of DNA come into contact with each other, exchange between the
sections of each DNA takes place. This stage is called as crossing over during which, the DNA
breaks and is attached on the other DNA strand leading to the transfer of genes and possibly the
formation of new genes. This phenomenon is called as genetic recombination. Hence genetic
recombination is the transfer of DNA from one organism to another.
The donor DNA that got transferred may be integrated into the nucleoid of recipient bacteria by a
range of mechanisms. In homologous recombination, the DNA sequences having nearly the same
nucleotide sequences (termed as homologous) get exchanged by means of breakage followed by
reunion of paired DNA segments. Genetic information can be transferred from organism to
organism through vertical transfer (from a parent to offspring) or through horizontal transfer
methods such as transformation, conjugation and transduction.
Generally, bacterial genes are transferred to members of the same species but sometimes,
transfer of genes to other species can also happen.
3.3.1 Transformation
Transformation involves the uptake of free or naked DNA released by donor bacteria by a
recipient one. Transformation was the first example of genetic exchange in bacteria and has been
first ever demonstrated in an experiment conducted by Griffith in 1928 (in box 3.1).
It is basically a natural mode of gene transformation and has a large impact on lateral gene flow
in nature therefore remains a matter of speculation.
BACTERIAL GENETICS
Learning outcome:
By the end of this chapter, students should be able to;
1) Describes the mechanism of gene expression along with various elements controlling the
same in bacteria.
2) Discus mechanisms of genetic recombination in bacteria.
3) Explain the different mode of genetic recombination i.e. transformation, conjugation and
transduction.
4) Explain the involvement of bacteria in genetic manipulation of our food.
3.1 Introduction
Genetics is the study of heredity and variations. Genetic variation is the key to the survival of a
species, allowing a species to adapt to changes in their environment by natural selection. That's
true for bacteria as well. Like other living organisms, bacteria also multiply and pass on their
characteristics from generation to generation. There are also the possibilities of variations in a
small proportion in the inherited characters of their progeny.
Bacteria reproduce by binary fission. As a result of binary fission, bacteria produce clones or
genetically identical copies of the parent bacterium. Since the offspring bacteria are genetically
identical to the parent, binary fission doesn't provide an opportunity for genetic recombination or
genetic diversity (apart from the occasional random mutation) in bacteria. The three other
mechanisms responsible for transfer of genetic materials take place in bacteria. These are termed:
as transformation, conjugation and transduction.
3.2 Genetic recombination in bacteria
Bacteria can transfer genes from one strain to another by three different mechanisms:
transformation, conjugation and transduction, these events clearly show the universality of
sexuality in the living world. The genetic recombination in bacteria has a very vital significance.
Some of them are as follow:
Transfer of antibiotic resistance genes: The remarkable spread of resistance to multiple
antibiotics may have been aided by the transfer of resistance genes within populations
and among species.
, As a tool to study advances of molecular biology and biotechnology: Many bacteria
have enzymes that enable them to destroy foreign DNA that gets into their cells. It seems
unlikely that these would be needed if that did not occur in nature. In addition, the prime
enzymes of bacterial reproduction namely restriction endonucleases have provided the
tools of molecular biology. Most of the advances in biotechnology industry directly
depend on the use of these enzymes.
Study of Evolution: The recent completion of the sequence of the entire genome of a
variety of bacteria (and archaea) suggests that in the past the genes have moved from one
species to another by horizontal gene transfer.
3.3 Transfer of genetic material
Whenever two fragments of DNA come into contact with each other, exchange between the
sections of each DNA takes place. This stage is called as crossing over during which, the DNA
breaks and is attached on the other DNA strand leading to the transfer of genes and possibly the
formation of new genes. This phenomenon is called as genetic recombination. Hence genetic
recombination is the transfer of DNA from one organism to another.
The donor DNA that got transferred may be integrated into the nucleoid of recipient bacteria by a
range of mechanisms. In homologous recombination, the DNA sequences having nearly the same
nucleotide sequences (termed as homologous) get exchanged by means of breakage followed by
reunion of paired DNA segments. Genetic information can be transferred from organism to
organism through vertical transfer (from a parent to offspring) or through horizontal transfer
methods such as transformation, conjugation and transduction.
Generally, bacterial genes are transferred to members of the same species but sometimes,
transfer of genes to other species can also happen.
3.3.1 Transformation
Transformation involves the uptake of free or naked DNA released by donor bacteria by a
recipient one. Transformation was the first example of genetic exchange in bacteria and has been
first ever demonstrated in an experiment conducted by Griffith in 1928 (in box 3.1).
It is basically a natural mode of gene transformation and has a large impact on lateral gene flow
in nature therefore remains a matter of speculation.
