Complete Nucleotide Sequence of a Novel Plasmid pAT23 from Halopiger sp. AT23 Isolated from Living Stromatolites in the Argentinean Puna

Abstract

Living or ‘modern’ stromatolites are mostly found in hypersaline lakes and marine lagoons with extreme conditions. The most recently found and as yet oldest living stromatolites were discovered by our lab in February 2009, in Laguna Socompa and Tolar Grande, in Salta province, Argentina; at about 4,000 m. A collection of Archaea isolated from these stromatolites has been established. Among the domain of the Archaea, haloarchaea are considered suitable for the study of archaeal genetics and a rich source of plasmids as well. The main of this work was the isolation, sequencing and bioinformatic analysis of plasmid pAT23 from Halopeiger sp. strain AT23, a haloarchaea isolated from living stromatolites. Plasmid DNA was isolated by QIAGEN Plasmid Mini Kit and sequenced by Sanger technology followed by standard bioinformatic analyses. DNA sequence of a novel plasmid pAT23 (7,843 bp) from haloarchaeal Halopeiger sp. AT23 was determined. A total of 15 open reading frames (ORFs) were identified; putative functions were assigned to 4 of them among others with no annotatable function. Regarding the replication region, one ORF was found with significant homology to the RepA of Halorubrum marismortui. Analysis of the nucleotide sequence also revealed the presence of type 1 fimbriae regulatory protein FimB as well as a protein PemK, responsible for mediating cell death through inhibiting protein synthesis through the cleavage of single-stranded RNA. The largest ORF encodes a putative RloA protein which shares homology with Lutella nitroferrum. pAT23 is a novel plasmid isolated from the halophilic archaeon Halopeiger sp. strain AT23, which has little homology with those haloarchaeal plasmids reported so far. To our knowledge this is the first report of the sequencing of a plasmid for the genus Halopeiger.