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Bacterial 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

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Bacterial plasmids

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  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

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