plasmid

plasmidi puhekieltä A loop of double-stranded DNA that is separate from and replicates independently of the chromosomes, most commonly found in bacterium bacteria, but also in archaeans and eukaryote eukaryotic cells, and used in genetic engineering as a vector for gene transfer.
1995, Christopher Howe, Gene Cloning and Manipulation, http://books.google.com.au/books?id=2m6mVdZWvfUC&pg=PA144&dq=%22plasmid%22%7C%22plasmids%22&hl=en&sa=X&ei=2Zt8U5PmJsKJlAXugYG4Ag&redir_esc=yv=onepage&q=%22plasmid%22%7C%22plasmids%22&f=false page 144:

This is how the F (for "fertility") plasmid, which forms the basis of a lot of classical E. coli genetics, is transferred from one cell to another.

Bacteria are happy to absorb little rings of DNA called plasmids and adopt them as their own.

Plasmids have an essential impact on productivity. Related factors are plasmid copy number, structural plasmid stability and segregational plasmid stability.