Red, Extremely Halophilic, but not Archaeal: The Physiology and Ecology of Salinibacter ruber, a Bacterium Isolated from
Solar saltern evaporation ponds, found in many locations worldwide in subtropical and tropical coastal areas, provide us with excellent model systems for the study of microbial processes at high salt concentrations.In multi-pond saltern environments a bro
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.1 Introduction Solar saltern evaporation ponds, found in many locations worldwide in subtropical and tropical coastal areas, provide us with excellent model systems for the study of microbial processes at high salt concentrations. In multi-pond saltern environments a broad range of salt concentrations is found, increasing from seawater (around 35 g dissolved salts per liter) to brines with salt concentrations exceeding 350 g l–1 (see, e.g., Rodriguez-Valera et al. 1981; Oren 1993; Litchfield et al. 2000). Many of the halophilic and halotolerant microorganisms in culture have been isolated from such salterns, and considerable efforts have been devoted toward the understanding of the microbial transformations in the water and the sediments of saltern evaporation and crystallizer ponds (Javor 1989; Oren 1993). When the NaCl concentration approaches saturation in the crystallizer ponds, the brines generally take on a red color due to the presence of dense communities of halophilic microorganisms. Similar red colors have been reported in many natural salt lakes as well, such as the Dead Sea and the Great Salt Lake (Oren 1993). The red coloration of the brines has thus far been attributed to the presence of two types of pigmented microorganisms: halophilic Archaea of the family Halobacteriaceae and b-carotene-rich cells of the unicellular green alga Dunaliella salina. Although many different species of halophilic Archaea have been isolated in the past from saltern crystallizer ponds, it is only recently that we have begun to understand the nature of the dominant component of the archaeal community in such ponds. Microscope examination shows that the most frequently encountered type of cell generally has a flat, square morphology, and A. Ventosa (Ed.) Halophilic Microorganisms © Springer-Verlag Berlin Heidelberg 2004
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often contains gas vesicles (Guixa-Boixareu et al. 1996; Oren et al. 1996). Cells with such a morphology have not yet been obtained in culture. Amplification of archaeal 16S rRNA genes from DNA extracted from the biomass of the saltern crystallizers of Santa Pola (Alicante, Spain) and Eilat (Israel) consistently yielded a new phylotype at the highest frequency, distantly related to the genus Haloferax, but not yet represented by any cultured species (Benlloch et al. 1995, 1996; Rodríguez-Valera et al. 1999). The connection between this new archaeal phylotype and the as yet uncultured square bacteria was finally established when it was shown that fluorescent oligonucleotide probes designed to specifically interact with the new phylotype reacted with the flat square cells that dominate the community in the Alicante saltern crystallizer (Antón et al. 1999). Thus far, Bacteria were not thought to play a significant role in the biology of saltern crystallizer ponds. Those halophilic or highly halotolerant representatives of the bacterial domain that are known in culture compete poorly with the Archaea which are better adapted to life at the highest salt concentrations (Rodriguez-Valera et al.
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