5细菌的遗传和变异.ppt

Bacterial Genetics Xiao-Kui GUO PhD Bacterial Genomics Microbial Genomics 68% Deinococcus radiodurans Microbial Genome Features G+C content 29% 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 ? 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 ? 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 o