Polyploidy in archaea and bacteria: about desiccation resistance, giant cell size, long-term survival, enforcement by a eukaryotic host and additional aspects.

During recent years, it has become clear that many species of archaea and bacteria are polyploid and contain more than 10 copies of their chromosome. In this contribution, eight examples are discussed to highlight different aspects of polyploidy in prokaryotes. The species discussed are the bacteria Azotobacter vinelandii, Deinococcus radiodurans, Sinorhizobium meliloti, and Epulopiscium as well as the archaea Methanocaldococcus jannaschii, Methanococcus maripaludis, Haloferax volcanii, and haloarchaeal isolates from salt deposits. The topics include possible laboratory artifacts, resistance against double-strand breaks, long-term survival, relaxation of DNA segregation and septum formation, enforced polyploidy by a eukaryotic host, genome equalization by gene conversion, and the nongenetic usage of genomic DNA as a phosphate storage polymer. Together, the selected topics give an overview of the biodiversity of polyploidy in archaea and bacteria.