Fate of compatible solutes during dilution stress in Ectothiorhodospira marismortui

Ectothiorhodospira marismortui, a halophilic purple sulfur bacterium isolated from a sulfur spring on the shore of the Dead Sea, accumulates three organic solutes to achieve osmotic balance with the medium: glycine betaine, N(α)-carbamoyl-L-glutamine 1-amide (CGA), and a minor amount of sucrose. When cells were subjected to dilution stress, part of the glycine betaine was excreted into the medium during the first 5-10 min, to be taken up again at a later stage. Intracellular concentrations of both CGA and sucrose decreased within 1-2 h to a new level corresponding with the lowered salinity. Neither CGA, nor sucrose appeared in the medium, showing that these compounds are metabolized intracellularly. When the decrease in intracellular CGA concentration was followed by assays for amide groups and for carbamoyl groups, it appeared that the decrease in carbamoyl groups containing material was much more rapid than the decrease in amide groups, suggesting L-glutamine 1-amide as a possible intermediate of CGA degradation.