plásmidos

Plásmidos are small, circular DNA molecules that replicate independently of the chromosomal DNA in many bacteria, and occasionally in archaea and some fungi. They are usually extrachromosomal and not essential for everyday survival, but they can provide advantageous traits under certain conditions, such as the presence of antibiotics or other environmental stresses.

Most plásmidos carry a limited set of genes, often organized into functional modules. Common features include an origin of replication (ori) that determines copy number, genes for selective markers, and maintenance systems that ensure the plasmid is inherited during cell division. Plásmidos vary in size from a few thousand to several hundred thousand base pairs and differ in copy number, from single-copy (or low-copy) to high-copy plasmids, which exist in multiple copies per cell. Some carry toxin-antitoxin systems that help stabilize them in populations.

Transmission between cells occurs primarily through horizontal gene transfer. Conjugative plasmids encode transfer genes (tra) and can move themselves to recipient cells via direct contact. Other plasmids are mobilizable or can spread with the help of conjugative elements. Plásmidos frequently carry genes that influence bacterial traits, including antibiotic resistance genes (R plasmids), metabolic enzymes, virulence factors, or bacteriocins. They can also participate in genetic rearrangements, host-range expansion, and the rapid adaptation of microbial communities.

In biotechnology, plásmidos are widely used as cloning and expression vectors. They enable insertion and expression of foreign genes, with features such as multiple cloning sites, selectable markers, and defined origins of replication. Their use requires careful consideration of biosafety and regulatory guidelines, given their potential role in spreading resistance or virulence traits. Classic examples include the F plasmid, Col plasmids, R plasmids, and laboratory cloning vectors like pBR322 and pUC series.