Chapter 7 Microbial Genetics Plasmids Circular genetic elements that reproduce autonomously and have an extra-chromosomal existence. ·1-1000 KB in size Typical plasmid 1/20 of chromosome Most are circular double-stranded DNA. some linear ds dna Transmitted from cell to cell via conjugation process Some can integrated into chromosome Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals et al
Chapter 7 Microbial Genetics Plasmids • 1-1000 KB in size • Typical plasmid 1/20 of chromosome • Most are circular double-stranded DNA, some linear ds DNA • Transmitted from cell to cell via conjugation process • Some can integrated into chromosome • Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals et al. Circular genetic elements that reproduce autonomously and have an extra-chromosomal existence:
Plasmid Conjugative: plasmids which govern their own transfer by cell-to-cell contact are called conjugative Tra region: a set of genes within the plasmid that control the transmissability by conjugation Hfr(high frequency of recombination): strains of bacteria that transfer large amounts of chromosomal dna during conjugation Supercoil: plasmids isolated from the cells are in supercoiled configuration Curing of plasmids: elimination of plasmids from host cel Plasmid separation: by ultracentrifugation or electrophores by various treatments
Plasmid • Conjugative: plasmids which govern their own transfer by cell-to-cell contact are called conjugative • Tra region: a set of genes within the plasmid that control the transmissability by conjugation • Hfr (high frequency of recombination): strains of bacteria that transfer large amounts of chromosomal DNA during conjugation • Supercoil: plasmids isolated from the cells are in supercoiled configuration • Plasmid separation: by ultracentrifugation or electrophoresis • Curing of plasmids: elimination of plasmids from host cells by various treatments
Plasmids Replication: Most plasmids of gram-positive bacteria replicate by a rolling circle mechanism Copy number: The number of plasmids in a cell, can range from only 1-3 copies to 100 copies. Incompatibility: Two different types of Plasmids can not coexist in a cell pl Episomes: Plasmids having the ability to integrate into host chromosome
Plasmids • Replication: Most plasmids of gram-positive bacteria replicate by a rolling circle mechanism. • Copy number: The number of plasmids in a cell, can range from only 1-3 copies to 100 copies. • Incompatibility: Two different types of plasmids can not coexist in a cell. • Episomes: Plasmids having the ability to integrate into host chromosome
F-Plasmid-Fertility plasmids 1s3 100KB Tn1000 Can be cured with 1000 acridine orange tra region s· compatibility(imc) Origin of replication (oriS) Transposable elements 75 25 tra region phi: phage inhibition Is (insertion sequence) rep: replication functions inc, rep, oris, phi
F-Plasmid-Fertility Plasmids • 100 KB • Can be cured with acridine orange • Incompatibility (inc) • Origin of replication (oriS) • Transposable elements (Tn) • tra region • phi: phage inhibition • IS (insertion sequence) • rep: replication functions
Cell to Cell transfer of plasmids Conjugative: Plasmids that govern their own transfer by cell-to-cell contact are called conjugative(not all plasmids are conjugative) Some conjugative plasmids can transfer genetic information between distintly related organisms (between gram-positive and gram-negative bacteria, between bacteria and plant cells, and between bacteria and fungi), it is important for evolution. Chromosome Plasmid Conjugation(接合作用)
Cell to Cell Transfer of Plasmids • Conjugative: Plasmids that govern their own transfer by cell-to-cell contact are called conjugative (not all plasmids are conjugative) • Some conjugative plasmids can transfer genetic information between distintly related organisms (between gram-positive and gram-negative bacteria, between bacteria and plant cells, and between bacteria and fungi), it is important for evolution. Conjugation (接合作用）