| Summary: | The soda lakes of the Rift Valley, Kenya, are a group of closed-basin alkaline saline lakes The most extreme example in the Rift Valley is Lake Magadi, where semi-solid trona deposits fill the lake, and are rained commercially, present the lakes are isolated from one another, although this may not have always been the case. Microbiological investigations of these lakes have shown that, characteristic phototrophic bacteria and extremely halophilic archaebacteria occur abundantly under certain conditions. The phototrophic bacteria observed at the lakes include Chloroflexus-like organisms of the hot springs, and organisms resembling members of the genus Ectothiorhodospira. Ectothiorhodospira-like organisms isolated from the lakes were similar to Ectothiorhodospira mobills and Ectothiorhodospira shaposhnikovii, in their physiology and biochemistry but could be divided into two groups on the basis of the occurrence of gas vacuoles in one group. These organisms, which deposit sulphur outside the cell during the photooxidation of sulphide to sulphate, constitute an ecological and physiological group adapted to life in the soda lakes. The taxonomic relationships of the organisms isolated from the lakes is discussed, including the taxonomic status of the gas vacuolate and extremely halophilic organisms of the Ectothiorhodospira group. The extremely halophilic archaebacteria isolated from Lake Eagadi were similar to known archaebacterial extreme halophiles in their possession of ether linked lipids, NaCl requirement, and the lack of muramic acid in the cell wall but were different in other respects, including adaption to low Hg2+- concentrations and pH 9.0-10.0. The organisms constitute an ecological and physiological group within the extremely halophilic archaebacteria and their taxonomic relationship is discussed.
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