Journal
INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY
Volume 51, Issue -, Pages 1133-1142Publisher
SOC GENERAL MICROBIOLOGY
DOI: 10.1099/00207713-51-3-1133
Keywords
Natrialba aegyptiaca sp nov.; Natrialba asiatica; extremely halophilic archaeon; exopolymer; poly(glutamic acid)
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A novel extremely halophilic member of the Archaea, strain 40(T), was isolated from Egypt (Aswan). This isolate requires at least 1.6 M sodium chloride for growth and exhibits optimal growth between 37 and 42 degreesC. Determination of the entire 16S rRNA gene sequence revealed the highest similarity to the type strain of Natrialba asiatica (> 99 %). Polar lipid analysis indicated that strain 40T and Natrialba asiatica have essentially identical compositions, indicating that the former is a member of genus Natrialba. However, physiological and biochemical data provided evidence that Natrialba asiatica strains B1T and 172P1(T), as well as strain 40(T), are sufficiently different to be divided in three different species. The G+C content of strain 40(T) was 61.5 +/-0.6 mol%. In addition, DNA-DNA hybridization data supported the placement of the isolate in a new species in the genus Natrialba, Natrialba aegyptiaca sp. nov., and indicated that Natrialba asiatica strain B1T should also be placed in a separate species, Natrialba taiwanensis sp. nov. Morphological studies of strain 40T indicated clearly that this isolate appears in three completely different cell shapes (cocci, rods, tetrads) under different conditions of growth, including different sodium chloride concentrations and different growth temperatures. Another interesting property of strain 40T is the ability to produce an extracellular polymer, which was found to be composed predominantly of glutamic acid (85% w/w), representing poly(glutamic acid), carbohydrates (12.5 % w/w) and unidentified compounds (2.5 % w/w). Among the Archaea, production of an extracellular polysaccharide has been described for some members of the genera Haloferax and Haloarcula.
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