Osmotic Adaptation in Halophilic and Halotolerant Microorganisms

Abstract

Although the majority of microorganisms live in freshwater or marine habitats, numerous microbes are well adapted to grow under hypersaline conditions. Osmotica must necessarily be compatible solutes, though compatible solutes need not necessarily be osmotica, i.e., accumulation can be caused by processes other than osmotic adaptation. A more detailed discussion of osmotic adaptation by algae, including a description of the enzymatic reactions involved in the synthesis of osmotica, are given by Ben-Amotz and Avron and Wegmann. Osmotic adaptation of halobacteria, methanogenic bacteria, halophilic eubacteria, Escherichia coli and enterobacteria, and Haloanaerobiaceae is discussed in this chapter. This terminology, however, is misleading, because red-colored extremely halophilic eubacteria exist within the genus Ectothiorhodospira, a group of phototrophic purple sulfur bacteria with salt optima equal to or even higher than those of most of the presently known representatives of the halobacteria.

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