Pathogenicity Island
Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. They are incorporated in the genome of pathogenic organisms, but are usually absent from those nonpathogenic organisms of the same or closely related species. These mobile genetic elements may range from 10-200 kb and encode genes which contribute to the virulence of the respective pathogen. Typical examples are adherence factors, toxins, iron uptake systems, invasion factors and secretion systems. Pathogenicity islands are discrete genetic units flanked by direct repeats, insertion sequences or tRNA genes, which act as sites for recombination into the DNA. Cryptic mobility genes may also be present, indicating the provenance as transduction.
One species of bacteria may have more than one PAI (i.e. Salmonella has at least 5). They are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon.
An analogous genomic structure in rhizobia is termed a symbiosis island.
Read more about Pathogenicity Island: Properties, Examples
Famous quotes containing the word island:
“When the inhabitants of some sequestered island first descry the “big canoe” of the European rolling through the blue waters towards their shores, they rush down to the beach in crowds, and with open arms stand ready to embrace the strangers. Fatal embrace! They fold to their bosoms the vipers whose sting is destined to poison all their joys; and the instinctive feeling of love within their breasts is soon converted into the bitterest hate.”
—Herman Melville (1819–1891)