Electron-microscopic examination of water samples from the hypersaline Dead Sea showed the presence of high numbers of virus-like particles. Between 0.9 and 7.3 × 107 virus-like particles ml-1 were enumerated in October 1994 in the upper 20m of the water column during the decline of a bloom of halophilic Archaea. Virus-like particles outnumbered bacteria by a factor of 0.9-9.5 (average 4.4). A variety of viral morphologies were detected, the most often encountered being spindle-shaped, followed by polyhedral and tailed phages. In addition, other types of particles were frequently found, such as unidentified algal scales, and virus-sized star-shaped particles. Water samples collected during 1995 contained low numbers of both bacteria and virus-like particles (1.9-2.6 × 106 and 0.8-4.6 × 107 ml-1 in April 1995), with viral numbers sharply declining afterwards (less than 104 ml-1 in November 1995-January 1996). It is suggested that viruses may play a major role in the decline of halophilic archaeal communities in the Dead Sea, an environment in which protozoa and other predators are absent.
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Acknowledgments We thank D.A. Anati for contributing data on Dead Sea water temperature and salinity. This study was supported by the EU MAST programme, contract number MAS3-CT95 0016 MEDEA (through Frede Thingstad to GB and MH), by the Israel Science Foundation administered by the Israel Academy of Sciences and Humanities and by the Israeli Ministry of Energy and Infrastructure. The electron microscopy work was done at the Laboratory for Electron Microscopy, University of Bergen.
- Dead Sea
- Virus-like particles