Halorubrum hochsteinianum sp. nov., an ancient haloarchaeon from a natural experiment.

A single extremely halophilic strain was isolated from salt brine produced when a fresh water lake flooded a large salt mine located beneath the lake. The water that entered this mine contained less than 0.34 M NaCl, but over time, this sealed brine became saturated by Cenozoic age salt (121-125 million-year BCE). The isolated strain requires at least 1.7 M NaCl for survival and grows optimally in 3.1 M NaCl. Therefore, it could not have survived or been present in the waters that flooded this salt mine. The strain grows at a pH range from 6.5 to 9.0 and has a wide tolerance to temperatures from 25 ℃ to at least 60 ℃. The comparison of 16S rRNA and rpoB' genes revealed that strain 1-13-28^T is related to Halorubrum tebenquichense DSM 14210^T showing 98.6% and 98.1% similarities, respectively. Phylogenetic analyses based on 16S rRNA, rpoB' genes and 122 concatenated archaeal genes show that the strain 1-13-28^T consistently forms a cluster with Halorubrum tebenquichense of the genus Halorubrum. Strain 1-13-28^T contained sulfated mannosyl glucosyl diether, and the polar lipid profile was identical to those of most Halorubrum species. Based on the overall combination of physiological, phylogenetic, polar lipids and phylogenomic characteristics, strain 1-13-28^T (= ATCC 700083^T = CGMCC 1.62627^T) represents a newly identified species within the genus Halorubrum for which the name Halorubrum hochsteinianum is proposed.