Competence (biology)
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In microbiology and cell and molecular biology, competence is the ability of a cell to take up extracellular ("naked") DNA from its environment. Competence is distinguished into natural competence, a genetically specified ability of Bacteria that is thought to occur under natural conditions as well as in the laboratory, and induced or artificial competence, arising when cells in laboratory cultures are treated with solutions or electric fields to make them transiently permeable to DNA. In the natural world DNA usually has become available by lysis of other cells, but in the laboratory it is provided by the researcher, often as a genetically engineered fragment or plasmid.
During uptake the DNA is transported across the cell membrane or membranes, and the cell wall if one is present. Once the DNA is inside the cell it may be degraded to nucleotides, which are reused for DNAS synthesis and other metabolic functions. Alternatively it may be incorporated into the cell’s genome by recombination. If this recombination changes the cell’s genotype the cell is said to have been transformed. Artificial competence and transformation are used as a research tool in many organisms, and are discussed in more detail under Transformation.
In the laboratory natural competence is usually tightly regulated and often triggered by nutritional shortages or poorly characterized adverse conditions. In bacteria capable of forming spores, conditions inducing sporulation often overlap with those inducing competence Thus cultures or colonies containing sporulating cells often also contain competent cells. Most competent bacteria are thought to take up all DNA molecules with roughly equal efficiencies, but bacteria in the families Neisseriaceae and Pasteurellaceae preferentially take up DNA fragments containing short DNA sequences that are very frequent in their own genomes. Neisserial genomes contain many copies of the preferred sequence GGCCGTCTGAA, and Pasteurellacean genomes contain either AAGTGCGGT or ACAAGCGGT, with corresponding biases of their DNA uptake machinery.
The evolutionary functions of natural competence are controversial. In principle, competence could allow cells to replace heavily damaged DNA in the cell's genome if needed, and recombination of DNA containing different genes or versions of genes contributes to the genetic diversity that makes evolution possible (as mentioned by most textbooks and researchers). However, according to another interpretation, the largest and most straightforward benefit of DNA uptake in the natural world is probably the nucleotides obtained by breaking down the DNA once it is inside the cell[citation needed]. In any case, most cells are not naturally competent. Competence can be increased by increasing the concentration of calcium ions, providing a cold treatment, and subjecting the cells to electroporation.
