Intracellular salt and solute concentrations in Ectothiorhodospira marismortui: glycine betaine and Nα-carbamoyl glutamineamide as osmotic solutes

Ectothiorhodospira marismortui, a moderately halophilic purple sulfur bacterium from a hypersaline sulfur spring, contains glycine betaine and Nα-carbamoyl glutamineamide (CGA) as the main intracellular osmotic solutes, with sucrose as a minor component. The concentration of glycine betaine was found to increase with increasing salt concentration of the medium, from 0.47 M to 1.29 M in cells grown from 0.85 to 2.56 M NaCl, while the estimated CGA concentration rose from about 0.2 M to 0.5 M. The concentration of sucrose remained constant at a value of around 0.05 M. Intracellular sodium and potassium concentrations were relatively low (around 0.5 and 0.3 M, respectively, at an external NaCl concentration of 1.8 M). The concentration of the novel compound Nα-carbamoyl glutamineamide was enhanced when l-glutamine was added to the growth medium, suggesting that glutamine served as a precursor for the synthesis of the compound.