Characterization of the dominant halophilic archaea in a bacterial bloom in the dead sea

A mass bloom of halophilic archaea developed in the Dead Sea in the summer of 1992, with peak densities of more than 3 × 107 cells/ml, imparting a red coloration to the water. Microscopical examination showed a numerical dominance of pleomorphic, flat cells. Attempts to identify the dominant type of halophilic archaea by means of growth experiments, both on agar plates and by dilution in liquid media, were unsuccessful, as viable counts obtained were two or more orders of magnitude lower than the total microscopic counts. Analysis of the polar lipids in the Dead Sea biomass during the bloom showed one major glycolipid to be present in the extracts, corresponding with the sulfated diglycosyl diether lipid (S-DGD-1) characteristic of the genus Haloferax. No indications were found for the presence of significant amounts of other glycolipids that indicate the presence of large numbers of Dead Sea archaea such as Halobacterium sodomense or Haloarcula marismortui, or Halobacterium species such as H. halobium, H. salinarium and H. saccharovorum. Thus, the numerically dominant organisms in the bloom is probably a difficult to culture, not yet isolated, representative of the genus Haloferax.