Plasmid incompatibility

May 26, 2021 Gaurab Karki Microbial Genetics 0




Plasmid incompatibility
Plasmid incompatibility

Plasmid incompatibility:

  • The inability of two or more plasmids to coexist stably in the same cell is known as Plasmid incompatibility.
  • This function of plasmids is controlled by the ori
  • Many bacteria contain more than one type of plasmid. However, These types of plasmid, they coexist stably in the bacterial cell. Even after many cell generations, they may remain in it.
  • Sometimes two plasmids of different types cannot coexist stably in the same cell.
  • As the cells multiply, one or the other plasmid is lost in this case.
  • When two plasmids cannot coexist stably, then they are said to be members of the same incompatibility (Inc) group.
  • They will belong to different Inc groups if two plasmids can coexist stably.
  • Plasmids can be incompatible in many ways:
    • If they can each regulate the other’s replication plasmid
    • if they share the same partitioning (par) functions.
  • In such a case, for the utilization of initiator protein, competition may occur.
  • Plasmids are usually classified by the Inc group to which they belong. Example:
    • RP4 (also called RK2) is an IncP (incompatibility group P) plasmid.
    • RSF1010 is an IncQ plasmid.
  • Plasmid incompatibility was first described for the F plasmid in E. coli strains in the early 1960s.
  • When any new plasmid is identified, it will be classified based on the incompatibility relationship with the known plasmids.
  • This may even lead to the creation of an entirely new class of incompatibility groups.
  • Plasmid incompatibility is an important consideration in designing any plasmid transfer experiment.
  • It is also crucial in selecting a cloning vector for genetic engineering.

Incompatibility Due to Shared Replication Control:

  • Two plasmids can be incompatible if they share the same mechanism of replication control.
  • Since the two different plasmids cannot be recognized as different by the replication control system, so either plasmid may be randomly selected for replication.
  • The total copy number of the two plasmids will be the same, at the time of replication.
  • But one may be represented much less than the other.
  • Example:
    • A cell contains two types of plasmids, suppose, type A and type B. At the time of replication, randomly one type will be picked up. If type A is replicated, then, there will be two copies of type A and only one of type B plasmid. In the next round, type A will have a higher probability of being replicated and plasmid type B may gradually be lost.

Incompatibility Due to Partitioning

  • If two plasmids share the same Par (partitioning) system then they can be incompatible.
  • During the cell division, Par systems help in the segregation of plasmids or chromosomes into daughter cells.
  • In the normal condition, this system helps to ensure that both daughter cells get at least one copy of the plasmid.
  • It ensures neither daughter cell is cured of the plasmid.
  • But if the same Par system is shared by the coexisting plasmids, then, during the division one or the other is always distributed into the daughter cells.
  • Sometimes one daughter cell will receive one plasmid type and the other cell gets the other plasmid type.
  • It can produce the cured cells of one or the other plasmid.