Glycine betaine transport in Escherichia coli: osmotic modulation

Abstract

Exogenous glycine betaine highly stimulates the growth rate of various members of the Enterobacteriaceae, including Escherichia coli, in media with high salt concentrations (D. Le Rudulier and L. Bouillard, Appi. Environ. Microbiol. 46:152-159, 1983). In a nitrogen-and carbon-free medium, glycine betaine did not support the growth of E. coli either on low-salt or high-salt media. This molecule was taken up by the cells but was not catabolized. High levels of glycine betaine transport occurred when the cells were grown in media of elevated osmotic strength, whereas relatively low activity was found when the cells were grown in minimal medium. A variety of electrolytes, such as NaCl, KCI, NaH2PO4, K2HPO4, K2SO4, and nonelectrolytes like sucrose, raffinose, and inositol triggered the uptake of glycine betaine. Furthermore, in ceUs subjected to a sudden osmotic upshock, glycine betaine uptake showed a sixfold stimulation 30 min after the addition of NaCl. Part of this stimulation might be a consequence of protein synthesis. The transport of glycine betaine was energy dependent and occurred against a concentration gradient. 2,4-Dinitrophenol almost totally abolished the glycine betaine uptake. Azide and arsenate exerted only a small inhibition. In addition, N,N'dicyclohexylcarbodiimide had a very low inhibitory effect at 1 mM. These results indicated that glycine betaine transport is driven by the electrochemical proton gradient. The kinetics of glycine betaine entry followed the Michaelis-Menten relationship, yielding a K. of 35 ,uM and a V,.,. of 42 nmol min-' mg of protein-'. Glycine betaine transport showed considerable structural specificity. The only potent competitor was proline betaine when added to the assay mixtures at 20-fold the glycine betaine concentration. From these results, it is proposed that E. coli possesses an active and specific glycine betaine transport system which is regulated by the osmotic strength of the growth medium.

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].…”

High survival and stability rates of Escherichia coli dried in hydroxyectoine

“…Since hydroxyectoine apparently functions well as an extracellular (and/or periplasmic) bioprotector during drying, it was of interest to determine whether it can also protect the intracellular environment. Hydroxyectoine is accumulated by E. coli under high osmolarity conditions, but is not used as a carbon source [11,12], and therefore behaves like glycine betaine [15,16]. It should be possible, therefore, to load E. coli with hydroxyectoine simply by incorporating it into high osmolarity growth medium, after which desiccation tolerance can be assessed; the success of this loading strategy can be monitored by its effect on trehalose biosynthesis, which is expected to be reduced, as described for media supplemented with glycine betaine [17].…”

Relationship between osmoprotection and the structure and intracellular accumulation of betaines by Escherichia coli

“…Synthetic betaines help define the characteristics required for accumulation. Perroud and Le Rudulier [15] concluded that the carboxyl group is essential and that its close proximity to the quaternary nitrogen increases the inhibition of radiolabeled-glycine betaine uptake by analogues. Accumulation was not demonstrated; such work does not distinguish competitive accumulation from inhibition of an uptake port.…”