Bacterial genetics Xiao-Kui Guo PhD
Bacterial Genetics Xiao-Kui GUO PhD
Bacterial genomics Organisation Linear chromosomes Borrelia burgdorferi Streptomces coelicolor Multiple chromosomes Vibrio cholerae · Plasmids Borrelia burgdorferi I7 linear circular plasmids 50%g enome size plasmid replication, " decaying genes". ?Ag variation Transposons IS elements. phages found in most genomes Campylobacter has none Repeats
Bacterial Genomics
Microbial genomics Linear Replicons Streptomycetes Verrucomicrobiales Acidobacterium Chlamydia ynechocystis Anabena ●Myin○ Coprothermobacter Mycoplasma HolophagaT Bacillus Planctomycetes Actinomycetes 2 Cyanobacteria G+C Fusobacteria d agrob Bacteriodaceae Coxiella Firmicutes Chlorobi Gree sulfur Fibrobacter group 出○ Spirochetes Treponema Deyupooous Helicobacter Campylobacter Borrelia o Bacteria Thermus quificales Archaea Deinococcus Thermotogales Thermodesulfobacterium
Microbial Genomics
Number of chromosomes in bacteria Chromosome Species number Mbp Proteobacteria Vibrio cholerae 3.0&1 Rhodobacter sphearoides 3.1&0.9 Burkholderia cepacia 3.5,3.0&1.0 Brucella suis 223332 3.2,2.0&1.1 Rhizobium meliloti 3.5,17&1.4 Agrobacterium tumefaciens 3.0&2.1 Other examples Die enococcus radiodurans 2 2.6&0.41 Borrelia burgdorferi >7(2)0.9t00.026 Leptospira interrogans 4.5&0.35 Red- rRNA genes on multiple chrms Green-important housekeeping genes on multiple chrms Blue- similar replicons present in all natural isolates
Chromosome ploidy pecies orms/cell Escherichia coli Dienococcus radiodurans -10 Borrelia hermsii 13-18 Azotobacter vinlandii >50 Buchnera ~100 Epulopiscium upto>1,000 r varies with growth stage
Microbial genome features 29%←G+ C content→68% Borrelia Deinococcus burgdorferi radiodurans single circular chromosome two circular Genome organization chromosomes+入 cIrcular chromosome plus one or more extrachromosomal large linear chromosome plus 21 extrachromosomal elements elements
68% Deinococcus radiodurans Microbial Genome Features 29% G+C content Borrelia burgdorferi Genome organization single circular chromosome large linear chromosome plus 21 extrachromosomal elements circular chromosome plus one or more extrachromosomal elements two circular chromosomes
PLASMIDS Plasmids are extrachromosomal genetic elements capable of autonomous replication. An episome is a plasmid that can integrate into the bacterial chromosome Classification of Plasmids Transfer properties y Conjugative plasmids Nonconjugative plasmids Phenotypic effects V Fertility plasmid(F factor) Y 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 Classification of Plasmids ➢ Transfer properties ✓ Conjugative plasmids ✓ Nonconjugative plasmids ➢ Phenotypic effects ✓ Fertility plasmid (F factor) ✓ Bacteriocinogenic plasmids. ✓ Resistance plasmids 7 factors)
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, 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 c, Importance 2-1 Mutation-The introduction of an insertion sequence into a bacterial gene wil result in the inactivation of the gene Hi) Plasmid insertion into chromosomes- The sites at which plasmids insert into the bacterial chromosome are at or near insertion sequence in the chromosome Phase Variation- The flagellar antigens are one of the main antigens to which the immune response is 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' attac Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface gens. Also the mechanism of phase variation may differ in different species of bacteria(e. g Neisseria transformation) ABCDEFG Transposase GFEDCRA
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, 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. • 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 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 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)
Transposons(Tn)-Transposons are transposable genetic elements that carry one or more other genes in addition to those which are essential for transposition o Nomenclature- Transposons are given the designation Tn followed by a number Structure- The structure of a transposon is similar to that of an insertion sequence, The extra genes are located between the terminal repeated sequences. In some instances (composite transposons)the terminal repeated sequences are actually insertion sequences Importance- Many antibiotic resistance genes are located on transposons Since transposons can jump from one DNa molecule to another, these antibiotic resistance transposons are a major factor in the development of plasmids which can confer multiple drug resistance on a bacterium harboring such a plasmid. These multiple drug resistance plasmids have become a major medical problem because the indiscriminate use of antibiotics have provided a selective advantage for bacteria harboring these plasmids. Is Resistance Gene(s) Is IS Resistance Gene(s) IS
Transposons (Tn) - Transposons are transposable genetic elements that carry one or more other genes in addition to those which are essential for transposition. • Nomenclature - Transposons are given the designation Tn followed by a number. • Structure - The structure of a transposon is similar to that of an insertion sequence. The extra genes are located between the terminal repeated sequences. In some instances (composite transposons) the terminal repeated sequences are actually insertion sequences. • Importance - Many antibiotic resistance genes are located on transposons. Since transposons can jump from one DNA molecule to another, these antibiotic resistance transposons are a major factor in the development of plasmids which can confer multiple drug resistance on a bacterium harboring such a plasmid. These multiple drug resistance plasmids have become a major medical problem because the indiscriminate use of antibiotics have provided a selective advantage for bacteria harboring these plasmids
These five PenicIllum expansum mutant strains express readily distinguishable changes in colony color and morphology
