文档介绍：Chapter8 Microbial ics
Plasmids
ic Conjugation,
Transformation, transduction
Transposons and Insertion Sequences
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 ic 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 bination): 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.
patibility: Two different types of plasmids can not coexist in a cell.
Episomes: Plasmids having the ability to integrate into host chromosome
Col plasmids
Bacteria also harbor plasmids with genes that may give them petitive advantage in the microbial word.
Bacteriocins are bacterial protein that destroy other bacteria. Usually act only against closely related strains
F-Plasmid-Fertility Plasmids
100 KB
Can be cured with acridine orange
patibility (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