Cut and stretch assay reveals resistance genes

Which antimicrobial resistance genes are present in bacteria, for example in a hospital ward? For laboratories with limited financial resources characterizing bacterial DNA is difficult, as this often requires expensive equipment. ...

Team develops automated platform for plasmid production

Plasmids have extensive use in basic and applied biology. These small, circular DNA molecules are used by scientists to introduce new genes into a target organism. Well known for their applications in the production of therapeutic ...

Two DNA defense systems behind resilience of 7th cholera pandemic

Cholera is caused by the bacterium Vibrio cholerae, a waterborne pathogen that infects the gut of humans through contaminated water and food. When ingested, V. cholerae colonizes the gut's inner surface, causing a watery ...

New immune system discovered in bacteria

Like humans, bacteria have various immune systems to defend against pathogens such as viruses. These immune systems usually degrade the DNA of the pathogens to make it harmless. In the research group of assistant Professor ...

page 1 from 6


In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular. Plasmids usually occur naturally in bacteria, but are sometimes found in eukaryotic organisms (e.g., the 2-micrometre ring in Saccharomyces cerevisiae).

Plasmid sizes vary from 1 to over 1,000 kbp. The number of identical plasmids in a single cell can range anywhere from one to even thousands under some circumstances. Plasmids can be considered part of the mobilome because they are often associated with conjugation, a mechanism of horizontal gene transfer.

The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.

Plasmids are considered "replicons", capable of autonomous replication within a suitable host. Plasmids can be found in all three major domains: Archaea, Bacteria, and Eukarya. Similar to viruses, plasmids are not considered by some to be a form of "life". Unlike viruses, plasmids are "naked" DNA and do not encode genes necessary to encase the genetic material for transfer to a new host, though some classes of plasmids encode the sex pilus necessary for their own transfer. Plasmid host-to-host transfer requires direct, mechanical transfer by conjugation or changes in host gene expression allowing the intentional uptake of the genetic element by transformation. Microbial transformation with plasmid DNA is neither parasitic nor symbiotic in nature, because each implies the presence of an independent species living in a commensal or detrimental state with the host organism. Rather, plasmids provide a mechanism for horizontal gene transfer within a population of microbes and typically provide a selective advantage under a given environmental state. Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or the proteins produced may act as toxins under similar circumstances. Plasmids can also provide bacteria with the ability to fix elemental nitrogen or to degrade recalcitrant organic compounds that provide an advantage when nutrients are scarce.

This text uses material from Wikipedia, licensed under CC BY-SA