Cryptic plasmids

In molecular biology, a cryptic plasmid is a plasmid that doesn't appear to provide any clear advantage to its host, yet still persists in bacterial populations.^[1] These plasmids appear to lack any genetic functions of interest and do not seem to contain genes that could provide beneficial functions to their hosts. Given the lack of a clear advantage to their hosts and the likely cost of maintaining them, these plasmids are often referred to as selfish elements or genetic parasites.^[1]The maintenance of cryptic plasmids might be explained by mechanisms like horizontal gene transfer (e.g., conjugation, transduction) that balance their loss due to segregation.^[2] However, cryptic plasmids could potentially be important in antibiotic resistance, by contributing to heteroresistance in bacterial populations. ^[3]

They have been found to be highly abundant, as seen in Lactobacillus where most plasmids are cryptic. ^[4]