1. Bacterial plasmids by
E. Börje Lindström

2. 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
- a movable genetic element
Transposon:

3. Different plasmids Grouped after their properties: F-plasmid /factor:
 100 kb

4. Different plasmids, cont.
- have genes for resistance against antibiotics and/or heavy metals
R- plasmid:
Size in kb pairs
Plasmid R100

5. 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

6. Plasmid genes Grouping
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
a certain amount of copies present per cell
controlled by the initiation frequency
low (1-4) to high (10-100)
Copy number:

7. 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

8. 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