Plasmids

Abstract

Plasmids are extrachromosomal elements common in bacteria and archea but also found in virally transformed eukaryotic cells. The study of plasmid biology has contributed significantly to understanding regulatory principles in chromosome replication and segregation, gene targeting, gene amplification, maintenance of genome identity, and genome evolution. However, the most profound impact of plasmids on life sciences has been through their use as cloning and expression vectors. Plasmids can also have remarkably broad host range that can cross species and even kingdom boundaries. Thus, plasmids are powerful agents for gene transfer, and by the same token, they are a potential risk to human health as they often carry genes for antibiotic resistance and virulence factors. Plasmids also carry useful genes, for example, those that encode functions capable of degrading organic pollutants or fixing nitrogen. Given the prevalence of plasmids in natural bacterial isolates, undoubtedly, much remains to be discovered about the roles they play.