5细菌的遗传和变异
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are at or near insertion sequence in the chromosome.
? iii) Phase Variation - The flagellar antigens are one of the main antigens to which the immune response is
which are involved in transposition. In between the terminal repeated sequences there are genes involved in transposition and sequences that can control the expression of the genes but no other nonessential genes are present.
Bacterial Genetics
Xiao-Kui GUO PhD
Hale Waihona Puke Baidu
Bacterial Genomics
Microbial Genomics
Microbial Genome Features
29% Borrelia burgdorferi
G+C content
68% Deinococcus radiodurans
single circular chromosome
two circular chromosomes
Genome organization
circular chromosome plus one or more extrachromosomal elements
large linear chromosome plus 21 extrachromosomal elements
Insertion sequences (IS)- Insertion sequences are transposable genetic
elements that carry no known genes except those that are required for transposition.
? a. Nomenclature - Insertion sequences are given the designation IS followed by a number. e.g. IS1 ? b. Structure Insertion sequences are small stretches of DNA that have at their ends repeated sequences,
? c. Importance ? i) Mutation - The introduction of an insertion sequence into a bacterial gene will result in the inactivation of
the gene.
? ii) Plasmid insertion into chromosomes - The sites at which plasmids insert into the bacterial chromosome
Transposons (Tn) - Transposons are transposable genetic elements
that carry one or more other genes in addition to those which are essential for transposition.
Classification of Plasmids
? Transfer properties ? Conjugative plasmids ? Nonconjugative plasmids ? Phenotypic effects ? Fertility plasmid (F factor) ? Bacteriocinogenic plasmids . ? Resistance plasmids 7 factors) .
PLASMIDS Plasmids are extrachromosomal genetic elements capable of
autonomous replication. An episome is a plasmid that can integrate into the bacterial chromosome
directed in our attempt to fight off a bacterial infection. In Salmonella there are two genes which code for two antigenically different flagellar antigens. The expression of these genes is regulated by an insertion sequences. In one orientation one of the genes is active while in the other orientation the other flagellar gene is active. Thus, Salmonella can change their flagella in response to the immune systems' attack. Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface antigens. Also the mechanism of phase variation may differ in different species of bacteria (e.g. Neisseria; transformation).
? iii) Phase Variation - The flagellar antigens are one of the main antigens to which the immune response is
which are involved in transposition. In between the terminal repeated sequences there are genes involved in transposition and sequences that can control the expression of the genes but no other nonessential genes are present.
Bacterial Genetics
Xiao-Kui GUO PhD
Hale Waihona Puke Baidu
Bacterial Genomics
Microbial Genomics
Microbial Genome Features
29% Borrelia burgdorferi
G+C content
68% Deinococcus radiodurans
single circular chromosome
two circular chromosomes
Genome organization
circular chromosome plus one or more extrachromosomal elements
large linear chromosome plus 21 extrachromosomal elements
Insertion sequences (IS)- Insertion sequences are transposable genetic
elements that carry no known genes except those that are required for transposition.
? a. Nomenclature - Insertion sequences are given the designation IS followed by a number. e.g. IS1 ? b. Structure Insertion sequences are small stretches of DNA that have at their ends repeated sequences,
? c. Importance ? i) Mutation - The introduction of an insertion sequence into a bacterial gene will result in the inactivation of
the gene.
? ii) Plasmid insertion into chromosomes - The sites at which plasmids insert into the bacterial chromosome
Transposons (Tn) - Transposons are transposable genetic elements
that carry one or more other genes in addition to those which are essential for transposition.
Classification of Plasmids
? Transfer properties ? Conjugative plasmids ? Nonconjugative plasmids ? Phenotypic effects ? Fertility plasmid (F factor) ? Bacteriocinogenic plasmids . ? Resistance plasmids 7 factors) .
PLASMIDS Plasmids are extrachromosomal genetic elements capable of
autonomous replication. An episome is a plasmid that can integrate into the bacterial chromosome
directed in our attempt to fight off a bacterial infection. In Salmonella there are two genes which code for two antigenically different flagellar antigens. The expression of these genes is regulated by an insertion sequences. In one orientation one of the genes is active while in the other orientation the other flagellar gene is active. Thus, Salmonella can change their flagella in response to the immune systems' attack. Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface antigens. Also the mechanism of phase variation may differ in different species of bacteria (e.g. Neisseria; transformation).