Glycine betaine, an osmotic effector in Klebsiella pneumoniae and other members of the Enterobacteriaceae

Abstract

Osmoregulation was examined in members of the Enterobacteriaceae. Exogenous glycine betaine at a concentration as low as 1 mM was found to stimulate the growth rate of Escherichia coli, Salmonella typhimurium, and Klebsiella pneumoniae in media of inhibitory osmotic strength. The stimulation was shown to be independent of any specific solutes, electrolytes, or nonelectrolytes. Therefore, the stimulatory effect of glycine betaine was a consequence of high osmotic potential. This effect was found to be far greater than the proline effect previously observed in S. typhimurium. Whereas nitrogen fixation by K. pneumoniae is completely inhibited under conditions of osmotic stress, nitrogenase activity could be partially restored by the addition of exogenous glycine betaine to the culture medium. Furthermore, glycine betaine in combination with proline, especially proline produced internally at a high level because of regulatory mutations affecting proline biosynthesis, strongly stimulated nitrogen fixation activity during osmotic stress. Glycine betaine was accumulated by the cells, and the amount taken up was correlated with the osmolarity of the medium. These findings are discussed in relation to the possible mechanisms by which glycine betaine might cause enhanced osmotolerance.

Salt tolerance in Rhizobium: A possible role for betaines

“…These values correspond to a concentration gradient of 1:45 and 1 : 770 for the cells grown in low-or high-salt medium, respectively [20]. This is in agreement with studies done with other bacteria such as Klebsiella penumoniae [16] and Escherichia coli [21].…”

“…Besides potassium, glutamate or (and) proline, glycine betaine, plays a major role in osmoregulation in the extremely halophilic phototrophic bacterium, Ectothiorhodospira halochioris [12], in the moderately halophilic bacterium Ba 1 [13], in some halophilic eubacteria [14], and also in several members of the Enterobacteriaceae [15][16][17]. Furthermore, enhancement of growth resulting from added glycine betaine and other betaines has been reported for several strains of R. meliloti grown under salt stress [18,19].…”

Osmoregulation and compatible solutes in eubacteria

“…The active component of the yeast extract was isolated and identified as glycine betaine. In some Enterobacteria, betaine not only increased the growth rate at any given salt concentration, which still permitted growth, but also extended the growth range of these bacteria towards higher salt concentrations [4]. The increased growth rates in the presence of betaine were related to an increased intracellular concentration of glycine betaine, which in turn was dependent on the external solute concentration [4].…”

“…If, however, 1 mM proline was added to the medium, the free glutamate pool decreased to about two thirds of its value in the absence of proline. Growth stimulation by external proline and partly reversion of salt inhibition under conditions of osmotic stress have been observed in a number of enterobacteria [4,7,63,[65][66][67], and proline is accumulated to high concentrations under these conditions. Growth of Salmonella oranienburg occurred at much higher osmolarities in complex media as compared to simple glucose mineral media, and much of this effect was ascribed to several amino acids in the medium, proline being regarded as the most important one [65].…”

“…Most eubacteria are non-halophilic or slightly halophilic, and most of the studies on osmoregulation have been done with bacteria of these two groups. Although NaC1 is the major solute which determines changes in osmolarity in the natural environment, it has been repeatedly shown that other non-penetrating solutes like KC1, (NH4)2SO4, K2SO 4, K2HPO 4, NaH2PO 4, and sucrose (but not penetrating solutes like glycerol and dimethylsulphoxide) induce the mechanisms of osmotic adaptation [3][4][5][6][7][8]. The osmotic and the ionic requirements can not easily be distinguished under saline conditions, because one may superimpose the other, but both may not necessarily be identical.…”