Multicopy single-stranded DNA ( msDNA ) is a type of DNA structure found outside the chromosomes in many cells.One of a type of so-called Satellite DNA. It was originally identified in the 1980's, in soil bacteria.
It's now known to be widely distributed in many species of bacteria.
The function of msDNA remains unknown even though many copies are present within cells. Knockout mutations that do not express msDNA are viable, so the production of msDNA is not essential to life under laboratory conditions. Over-expression of msDNA is mutagenic, apparently as a result of titrating out repair proteins by the mismatched base pairs that are typical of their structure. It has been suggested that msDNA may have some role in pathogenicity or the adaptation to stressful conditions. Source: Wikipedia