Transcript Bakterial plasmids

Bacterial plasmids
by
E. Börje Lindström
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 plasmids
Grouped after their properties:
• F-plasmid /factor:
 100 kb
Different plasmids, cont.
• R- plasmid:
- have genes for resistance
against antibiotics and/or heavy
metals
Size in kb pairs
Plasmid R100
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 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
•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:
• Host specificity/range:
- only a problem for low
and medium copy number
- 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