title: Halophilic archaea cultivated from surface sterilized middle-late eocene rock salt are polyploid.
abstract: Live bacteria and archaea have been isolated from several rock salt deposits of up to hundreds of millions of years of age from all around the world. A key factor affecting their longevity is the ability to keep their genomic DNA intact, for which efficient repair mechanisms are needed. Polyploid microbes are known to have an increased resistance towards mutations and DNA damage, and it has been suggested that microbes from deeply buried rock salt would carry several copies of their genomes. Here, cultivable halophilic microbes were isolated from a surface sterilized middle-late Eocene (38-41 million years ago) rock salt sample, drilled from the depth of 800 m at Yunying salt mine, China. Eight unique isolates were obtained, which represented two haloarchaeal genera, Halobacterium and Halolamina. We used real-time PCR to show that our isolates are polyploid, with genome copy numbers of 11-14 genomes per cell in exponential growth phase. The ploidy level was slightly downregulated in stationary growth phase, but the cells still had an average genome copy number of 6-8. The polyploidy of halophilic archaea living in ancient rock salt might be a factor explaining how these organisms are able to overcome the challenge of prolonged survival during their entombment.
authors.affiliation: Institute of Biotechnology and Department of Biosciences, University of Helsinki, Helsinki, Finland.
authors.forename: Salla T
authors.initials: ST
authors.lastname: Jaakkola
authors.affiliation: Institute for Molecular Biology, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Karolin
authors.initials: K
authors.lastname: Zerulla
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei, People's Republic of China.
authors.forename: Qinggong
authors.initials: Q
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Institute of Rock and Soil Mechanics, The Chinese Academy of Sciences, Wuhan, Hubei, People's Republic of China.
authors.forename: Hongling
authors.initials: H
authors.lastname: Ma
authors.affiliation: Institute of Rock and Soil Mechanics, The Chinese Academy of Sciences, Wuhan, Hubei, People's Republic of China.
authors.forename: Chunhe
authors.initials: C
authors.lastname: Yang
authors.affiliation: Institute of Biotechnology and Department of Biosciences, University of Helsinki, Helsinki, Finland.
authors.forename: Dennis H
authors.initials: DH
authors.lastname: Bamford
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei, People's Republic of China.
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Chen
authors.affiliation: Institute for Molecular Biology, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Soppa
authors.affiliation: Institute of Biotechnology and Department of Biosciences, University of Helsinki, Helsinki, Finland.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Oksanen
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D002681:China; D019641:DNA, Archaeal / Q000235:genetics*; D020745:Genome, Archaeal; D019015:Geologic Sediments / Q000382:microbiology; D006216:Halobacteriaceae / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010802:Phylogeny; D011123:Polyploidy; D012336:RNA, Ribosomal, 16S / Q000235:genetics*; D012492:Salts
chemical_list: D019641:DNA, Archaeal; D012336:RNA, Ribosomal, 16S; D012492:Salts