Osmoregulation and compatible solutes in eubacteria

Abstract

Osmotic adaption by halophilic and halotolerant bacteria is generally achieved by the accumulation or synthesis of several organic solutes. Accumulation by uptake from the medium is preferred over biosynthesis. The chemical nature of the major solute is important in determining the degree of osmotolerance of the organism. Glycine betaine accumulation confers a greater degree of osmotolerance than proline, which in turn confers more osmotolerance than glutamate accumulation. The occurrence and uptake of these solutes in a variety of eubacteria is reviewed.

True marine and halophilic anoxygenic phototrophic bacteria

“…In particular, significant differences have been observed regarding the requirement and growth responses of halophilic bacteria towards concentrations of the bivalent cations magnesium and calcium. Isolates from alkaline soda lakes that are almost devoid of magnesium and calcium demonstrate a requirement for minimum concentrations of these ions, 249 whereas bacteria from thalassohaline salt lakes and from the Dead Sea with much higher or very high concentrations of magnesium and calcium also have an increased requirement for these bivalent cations (see Imhoff 1986Imhoff , 1988Imhoff , 1993. These observations indicate that the concentrations of bivalent ions that support optimal growth reflect the environmental concentrations and that bacteria are adapted also to this aspect of their environment.…”

“…They may be required for specific transport processes, but need to be exported from the cytoplasm in most of the known prokaryotes by specific ion transport systems (Imhoff 1986(Imhoff , 1993. While the requirement of marine bacteria for inorganic ions, in particular sodium, is well established, the critical physiological or structural functions of high ion concentrations for the bacterial cells have not been identified.…”

Salt Stress

“…Salt stress tolerance in rhizobia is at least partially associated with osmoregulation achieved by accumulation of compatible solutes (Imhoff, 1986). Inn conditions of salt stress, pea plants treated with boron and calcium exhibited enhanced cell and tissue invasion by Rhizobium leguminosarum and increased nodule number (El-Hamdaoui et al, 2003).…”

The Properties of Water in Foods ISOPOW 6

“…Bacterial cells incubated under conditions of low water activity cope with the imposed stress primarily through the accumulation of compatible solutes (Imhoff, 1986;Galinski, 1993). Compatible solutes are those compounds that can be accumulated by cells to very high concentrations, sufficient to enable an outward turgor pressure to be sustained when the external osmotic pressure is high, without impairing enzyme activity.…”