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Plasmids are extrachromosomal DNA replicons separated from chromosomal DNA and capable of independent replication, usually in bacteria and archaea.
A plasmid is a small, extrachromosomal DNA molecule found in cells that is physically separate from chromosomal DNA and can replicate independently. Plasmids are most commonly small circular, double-stranded DNA molecules in bacteria and archaea, though they can also occur in eukaryotes. They often carry genes that provide advantages under specific conditions—such as antibiotic resistance, virulence factors, genes for secondary metabolism, and functions that support survival in harsh environments (including heavy-metal resistance and bioremediation). Because they are additional to the essential genetic information on chromosomes, plasmids typically contain “special circumstance” genes rather than the core genes required for normal growth. Core plasmid features include the presence of a DNA origin of replication (making the plasmid a replicon) and a regulated copy number, which can range from one to hundreds or more copies per cell. Plasmids may be circular or, less commonly, linear (linear plasmids require specialized end-replication mechanisms). For stable inheritance during cell division, low-copy-number plasmids often encode partition systems (e.g., parABS/parMRC) that help distribute plasmid copies to daughter cells. Plasmids can also integrate into host chromosomes in some cases (episomes), and they vary widely in size (from <1 kbp mini-plasmids to >400 kbp, including megaplasmids). Functionally, plasmids can be classified by their roles (e.g., conjugative/fertility, resistance, virulence, degradative) and by how they are transferred between hosts (conjugative, mobilizable, or non-conjugative).
Plasmids are extrachromosomal DNA replicons separated from chromosomal DNA and capable of independent replication, usually in bacteria and archaea.
Key features include an origin of replication, regulated plasmid copy number, and often partition systems for stable inheritance; plasmids can be circular or sometimes linear and may integrate as episomes.
Plasmids frequently carry adaptive genes (e.g., antibiotic resistance, virulence, metabolism/bioremediation) and are classified by transfer ability (conjugative, mobilizable, non-conjugative) and function (e.g., fertility, resistance, virulence, degradative).
A small extrachromosomal DNA molecule physically separated from chromosomal DNA that can replicate independently.
The self-replicating DNA unit of a plasmid that enables autonomous replication in a suitable host.
A DNA sequence on a plasmid that initiates plasmid DNA replication.
The number of plasmid molecules present in a single cell, determined by replication initiation regulation and plasmid size.
Plasmid-encoded mechanisms (e.g., parABS/parMRC) that help distribute plasmid copies to daughter cells during cell division.
A plasmid-like element that can integrate into the host chromosome in addition to replicating.
A plasmid that carries transfer genes enabling it to promote sexual conjugation and transfer to other cells.
A plasmid that carries only part of the transfer machinery and can be transferred at high frequency only with assistance from a conjugative plasmid.
A plasmid that cannot initiate conjugation and therefore requires other plasmids for transfer.
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