Definitions• Replicon: - a DNA-molecule with its own replication
• Plasmid: - a small extra-chromosomal replicon (autonomous)
- DS, closed molecule
- 1 – 1000 bp
• Episome: -a plasmid that can be integrated into the chromosome
- e.g. the F-plasmid
• Transposon: - a movable genetic element
Different plasmidsGrouped after their properties:
• F-plasmid /factor: 100 kb
Different plasmids, cont.• R- plasmid: - have genes for resistance
against antibiotics and/or heavy metals
Plasmid R100
Size in kb pairs
Different plasmids, cont.
• Col – plasmids: - produces colicins
- antibacterial
• Catabolic plasmids: -have properties to use odd carbon/ energy sources
- many Psuedomonas have such plasmids
• Cryptic plasmids: - no known property
Plasmid genesGrouping
1) Essential genes for keeping the plasmid within the cell
• Replication: -uses the replication system of the host cell
- have its own initiation, elongation and termination
- occurs during the entire cell cycle
•Copy number: -a certain amount of copies present per cell
- controlled by the initiation frequency
- low (1-4) to high (10-100)
Plasmid genes, cont.• Partitioning: - only a problem for low
and medium copy number
• Host specificity/range: - low to broad
2) Non-essential –important for transfer
• Are spread horizontally (among bacteria)
• Important genes
- pili-genes
- oriT
- tra/ mob genes
Plasmid genes, cont.
3) Non-essential –with surviving value
• Resistance against antibiotics
• Production of antibacterial substances (colicins)
• genes for pathogenesis/virulence
• genes to be able to use special energy/carbon sources, e.g. phenol