Halobacterial phylogeny and salt mine microbial ecology.

Salt deposits are the remains of ancient hypersaline waters, which presumably supported dense populations of halophilic archaebacteria (halobacteria). Winsford salt mine in Cheshire exploits salt from the Triassic period (195-225 Ma), and Boulby potash mine in Cleveland, which is Permian (225-270 Ma) has been mined since 1973. Halobacteria were isolated in large numbers from brine pools, crusts of recrystallised salt and solution-mining brine, and were even occasionally isolated from rock salt, in both salt mines. Eubacteria from Winsford brine pools are the first described aerobic, non-phototrophic, obligately halophilic eubacteria. Chemotaxonomy showed that most halobacte rial strains were similar to Halobacterium saccharovorum and representatives of the genus Haloarcula. This is a common feature of salt-saturated environments throughout the world. However, definite differences between most strains were revealed by 16S rRNA sequencing. Several salt mine strains were phylogenetically close to Hb. salinarium, despite having previously undescribed polar lipids. Strain Br3, isolated from a solution-mining brine, was most closely related to Halococcus morrhuae, but was subsequently found to be much more similar to a halococcus, isolated from Permian rock salt in Austria. A colourless strain (2Bbr13.2), isolated from a potash core in Boulby salt mine, had unusual polar lipids and morphology, and was also phylogenetically unrelated to any other halobacteria. Analysis of partial sequences demonstrated the diversity of the halobacteria, and served to develop signature sequences, to help in halobacterial identification. Discussion centres on whether salt deposit microorganisms are the descendants of populations entrapped when the salts were deposited, or whether they entered the mine in recent times.