Bacterial Plasmids Properties and Types

Bacterial Plasmids Properties and Types

February 18, 2022

Bacterial plasmids: Types of plasmids, Compatibility and incompatibility, Mobilizable plasmids, Copy number of plasmids, Fertility inhibition, Donation and conduction

  • Plasmids are extra chromosomal, covalently closed circular, stably inherited, autonomously replicating DNA molecule present in bacteria and in some lower eukaryotes.
  •  Plasmids are not required for bacterial growth however, confer additional advantage to bacteria in a particular environment. 
  • The plasmids are small in size generally 0.2-4% of the bacterial chromosome and their replication depends upon host metabolic machinery

Properties of plasmids

  • Autonomous replication
  •  Plasmids possess origin of replication which enable them to multiply independently.
  • The smaller plasmids use replication machinery of host for replication while larger plasmids code specific enzyme necessary for their replication in addition to host replication machinery. 
  • Some plasmid replicate by inserting themselves into the bacteria chromosome. 
  • These integrative plasmids (episomes) are stably maintained in this form through cell divisions but can also have abilty exist as independent elements.
  • Size and copy number 
  • Plasmid size ranges from 1.0 kb for the smallest to over 250 kb for largest plasmids. 

             Plasmid          Size         Organism

             ColE1              6.4          Pseudomonas and other E.coli

             F                    95            E.coli  

            TOL              117           Pseudomonas putida

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