Alcalilimnicola halodurans gen. nov., sp nov., an alkaliphilic, moderatelyhalophilic and extremely halotolerant bacterium, isolated from sediments of soda-depositing Lake Natron, East Africa Rift Valley

An alkaliphilic, halotolerant, Gram-negative, heterotrophic, aerobic and ro d-shaped organism was isolated from drying soda and at a water-covered site of Lake Natron, Tanzania, by means of the most-probable-number technique d eveloped for anoxygenic, phototrophic sulfur bacteria. It had an absolute r equirement for alkalinity, but not for salinity; growth occurred at salt co ncentrations of 0-28% (w/v), with optimal growth at 3-8% (w/v) NaCl. The ba cterium preferentially metabolized volatile fatty acids and required vitami ns for growth. The name Alcalilimnicola halodurans gen. nov., sp. nov. is p roposed for the novel isolate, placed in the gamma -Proteobacteria within t he family Ectothiorhodospiraceae on the basis of analysis of the 16S rDNA s equence, polar lipids, fatty acids and DNA base composition. Although Alcal ilimnicola halodurans is closely related to the extreme anoxygenic, phototr ophic sulfur bacteria of the genus Halorhodospira, it is not phototrophic.