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The term plasmid was coined in 1952 by the American molecular biologist Joshua Lederberg to refer to "any extrachromosomal hereditary determinant." [11] [12] The term's early usage included any bacterial genetic material that exists extrachromosomally for at least part of its replication cycle, but because that description includes bacterial viruses, the notion of plasmid was refined over time ...
A plasmid partition system is a mechanism that ensures the stable inheritance of plasmids during bacterial cell division. Each plasmid has its independent replication system which controls the number of copies of the plasmid in a cell. The higher the copy number, the more likely the two daughter cells will contain the plasmid.
An origin of transfer – A plasmid with no origin of transfer is non-mobilizable. [2] The transfer genes – Though a functioning set of tra genes is necessary for plasmid transfer, they may be located in a variety of places including the plasmid in question, another plasmid in the same host cell, or even in the bacterial genome. [3]
The F factor was the first plasmid to be discovered. Unlike other plasmids, F factor is constitutive for transfer proteins due to a mutation in the gene finO. [4] The F plasmid belongs to F-like plasmids, a class of conjugative plasmids that control sexual functions of bacteria with a fertility inhibition (Fin) system. [5]
The parABS system is a broadly conserved molecular mechanism for plasmid partitioning and chromosome segregation in bacteria.Originally identified as a genetic element required for faithful partitioning of low-copy-number plasmids, it consists of three components: the ParA ATPase, the ParB DNA-binding protein, and the cis-acting parS sequence.
Schematic drawing of bacterial conjugation. 1-Donor cell produces pilus.2-Pilus attaches to recipient cell, brings the two cells together.3-The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell.
Bacteria containing F-factors (said to be "F+") have the capability for horizontal gene transfer; they can construct a sex pilus, which emerges from the donor bacterium and ensnares the recipient bacterium, draws it in, [16] and eventually triggers the formation of a mating bridge, merging the cytoplasms of two bacteria via a controlled pore. [17]
The role of a plasmid in this pathogenic ability was further supported when large plasmids were found only in pathogenic bacteria but not avirulent bacteria. [11] Eventually, the detection of parts of bacterial plasmids in host plant cells was established, confirming that this was the genetic material responsible for the genetic effect of ...