Elements of microbial genetics and biotechnology:
Bacteria, viruses and fungi played crucial roles in understanding basic molecular mechanisms of genetic processes. The
knowledge obtained from studying these objects lef biology to the era of molecular genetics and molecular biology.
Bacterial chromosomal DNA: the storage of essential Bacterial plasmids are extrachromosomal, mostly circular, DNA
genetic information
The central dogma reflects the variety of mechanisms supporting stability of the genome that makes possible the existence
of the heredity and maintenance species. The most important genetic processes contributing to variation include:
mutations, recombination and transpositions.
Mutations: are random, inheritable (usually small) alterations in the sequences of a genome. Mutations can change the
phenotype.
1. Selectable mutations: could be selected after placing of organisms under conditions where their growth will be
favoured. Selectable mutations include:
a. Mutations of resistance (to antibiotics, heavy metals, osmotic stress etc.)
b. Mutations converting an auxotrophy to prototrophy (auxotrophy//protrophy = inability/ability to synthesise some
metabolite)
2. Non-selectable mutations: could be identified only after testing the whole population of an organism. Non-selectable
mutations include:
a. Mutations of auxotrophy
b. Mutations of sensitivity
Ex1. Antibiotic-resistant mutants could be easily selected as growing colonies on a background of inhibition zone
near the disc with antibiotic.
Ex2. Non-selectable (pigmented and non-pigmented) mutants of the fungus Aspergillus nidulans (the wild type
produces a green pigment; white colonies don’t produce the pigment; yellow pigment is an intermediate product
in the pathway of green pigment synthesis)
Point mutation is a mutation that involves a single base pair change.
1. Nonsense mutation: the codon becomes a stop codon and an incomplete polypeptide is made.
2. Missense mutation: the sequence of amino acids in the ensuing polypeptide is changed, resulting in a protein
with reduced activity or no activity.
3. Deletions and insertions are more dramatic alterations in DNA (ex. Frameshift mutations) that often result in
a complete loss of gene function
, Discovery of recombination in bacteria:
Recombination: the process by which parts or
all of the DNA molecules from 2 separate
sources are exchanged or brought together into
a single DNA molecule. Mechanisms of
recombination in prokaryotes involved DNA
transfer during any kind of genetic exchange
(transformation, conjugation and transduction)
Conjugation and fertility: Conjugation of Hfr bacteria:
The role of plasmid F factor in conjugation
Catabolic (degradative) plasmids: codes for enzymes degrading xenobiotics (substances for occurring in the biosphere).
Examples of plasmid-born resistance to metals:
- Enterobacteria: plasmids of resistance to ions of arsenic, silver,
copper, mercury, zinc.
- Pseudomonas sp.: resistance to ions of chromium, mercury,
tellurium
- Ralstonia metallidurans: resistant to high content of heavy
metals; possesses two large plasmids pMOL28 and pMOL30
Bacteria, viruses and fungi played crucial roles in understanding basic molecular mechanisms of genetic processes. The
knowledge obtained from studying these objects lef biology to the era of molecular genetics and molecular biology.
Bacterial chromosomal DNA: the storage of essential Bacterial plasmids are extrachromosomal, mostly circular, DNA
genetic information
The central dogma reflects the variety of mechanisms supporting stability of the genome that makes possible the existence
of the heredity and maintenance species. The most important genetic processes contributing to variation include:
mutations, recombination and transpositions.
Mutations: are random, inheritable (usually small) alterations in the sequences of a genome. Mutations can change the
phenotype.
1. Selectable mutations: could be selected after placing of organisms under conditions where their growth will be
favoured. Selectable mutations include:
a. Mutations of resistance (to antibiotics, heavy metals, osmotic stress etc.)
b. Mutations converting an auxotrophy to prototrophy (auxotrophy//protrophy = inability/ability to synthesise some
metabolite)
2. Non-selectable mutations: could be identified only after testing the whole population of an organism. Non-selectable
mutations include:
a. Mutations of auxotrophy
b. Mutations of sensitivity
Ex1. Antibiotic-resistant mutants could be easily selected as growing colonies on a background of inhibition zone
near the disc with antibiotic.
Ex2. Non-selectable (pigmented and non-pigmented) mutants of the fungus Aspergillus nidulans (the wild type
produces a green pigment; white colonies don’t produce the pigment; yellow pigment is an intermediate product
in the pathway of green pigment synthesis)
Point mutation is a mutation that involves a single base pair change.
1. Nonsense mutation: the codon becomes a stop codon and an incomplete polypeptide is made.
2. Missense mutation: the sequence of amino acids in the ensuing polypeptide is changed, resulting in a protein
with reduced activity or no activity.
3. Deletions and insertions are more dramatic alterations in DNA (ex. Frameshift mutations) that often result in
a complete loss of gene function
, Discovery of recombination in bacteria:
Recombination: the process by which parts or
all of the DNA molecules from 2 separate
sources are exchanged or brought together into
a single DNA molecule. Mechanisms of
recombination in prokaryotes involved DNA
transfer during any kind of genetic exchange
(transformation, conjugation and transduction)
Conjugation and fertility: Conjugation of Hfr bacteria:
The role of plasmid F factor in conjugation
Catabolic (degradative) plasmids: codes for enzymes degrading xenobiotics (substances for occurring in the biosphere).
Examples of plasmid-born resistance to metals:
- Enterobacteria: plasmids of resistance to ions of arsenic, silver,
copper, mercury, zinc.
- Pseudomonas sp.: resistance to ions of chromium, mercury,
tellurium
- Ralstonia metallidurans: resistant to high content of heavy
metals; possesses two large plasmids pMOL28 and pMOL30
