Life in the Dead Sea

Abstract

Tfhe Dead Sea is a saltwater lake bordered by Israel and Jordan. It lies in the Great Rift Valley that runs from Syria in south western Asia to Mozambique in southeastern Africa. Unlike river and glacial valleys which are produced by erosive forces, rift valleys are formed by the earth's crust being pulled apart by tectonic plate movement. Regarding the Rift Valley, it was the parting of the African and Arabian plates. The Dead Sea is the lowest point on the sur face of the earth; its shoreline is 1,312 feet be low sea level. The Jordan River flows southward from Syria into the Dead Sea. There is no out flow from the lake, but as it is located in a desert, extreme heat results in a high degree of evapora tion. The rate of evaporation exceeds water in flow. Consequently, the salinity of the Dead Sea is nine times greater than seawater. Owing to the high salt content the buoyant density of the wa ter makes floating easy but swimming difficult. Outstretched arms and legs are pushed up and float on the water's surface. Thus, the limbs are of little use in bringing about movement through the water. In addition, the high density of the water impedes swimming. The Dead Sea has a recorded history going back several millennia. It has not always been known by that name. In biblical times (Genesis 14:3, Joshua 3:16) it was known as the Salt Sea (and is still called the Salt Sea in modern Hebrew). It was later named the Dead Sea as no animal or plant life is found in its waters. Fish and aquatic plants carried in by the Jordan River are quickly killed by the high salt content of the water. Microorganisms were discovered in the sev enteenth century. At the time, owing to their minute size it was obvious they could have no effect on humans or other living things. Conse quently, the tiny life-forms were of no impor tance. That trend of thought continued for two hundred years. In the second half of the nine teenth century came a rude awakening. It was found that certain species of bacteria cause hu man diseases, some of which frequently resulted in death. Before long protozoa and micro-fungi were also discovered as agents of disease. Finally viruses were discovered, thus solving the mystery of why, for some infectious diseases, microorganisms could not be found as their causative agents. The role of microbes in disease was the impetus for wide-ranging studies of microorganisms, and before long microbiology became established as a major discipline in the biological sciences (Bardell, 2002). In the 1930s a Ph.D. student at Hebrew Uni versity in Israel turned his attention to the Dead Sea. Although devoid of animals and plants, could the hypersaline water be the habitat of microor ganisms? In 1936 came the first report of life in the Dead Sea (Volcani, 1936). Further pioneer ing studies by Volcani were published shortly thereafter (Volcani, 1940; 1943). The organisms found were unicellular green algae of the genus Dunaliella and several species of halophilic (salt loving) archaea and halophilic bacteria. Bacteria and archaea are prokaryotes. Prokary otic cells, unlike eukaryotic cells, do not have a nucleus. Their single chromosome is unbound in