Fplasmide

The Fplasmide, commonly known as the F plasmid, is a circular DNA molecule found in some strains of Escherichia coli and related bacteria. It is a conjugative plasmid that enables the transfer of genetic material between bacterial cells during conjugation, contributing to horizontal gene transfer. In its usual episomal form, the Fplasmide exists at a low copy number and is maintained across generations by plasmid maintenance systems.

The plasmid carries genes necessary for conjugation, including the transfer region (tra) and the origin of transfer (oriT). These elements enable the assembly of the mating pair and the formation of a contact channel through which a single DNA strand is transferred to a recipient cell, where synthesis restores the complementary strand. The Fplasmide can exist as an extrachromosomal element (F+), or it can integrate into the bacterial chromosome to form an Hfr (high-frequency recombination) strain, which can transfer portions of chromosomal DNA during mating.

Excision of the Fplasmide from the chromosome can generate F' plasmids that carry fragments of host DNA, allowing transfer of additional genes. The plasmid also encodes replication and maintenance functions, including systems that ensure stable inheritance in daughter cells, such as partitioning modules and sometimes toxin-antitoxin systems.

Applications and significance include serving as a classical model for studying bacterial conjugation and horizontal gene transfer. Fplasmide derivatives have been used in genetic engineering and cloning contexts, and the dynamics of F-like elements influence the spread of traits such as antibiotic resistance in bacterial communities.

History and context: the Fplasmide is one of the best-studied elements in bacterial genetics and has shaped understanding of microbial gene flow and evolution.