Glucosylglycerate is an osmotic solute and an extracellular metabolite produced by Streptomyces caelestis

Abstract

Streptomyces caelestis DSM 40084produces two osmolytes, viz. 2-O-(α-D-glucopyranosyl)-ξ-glyceric acid (GG) and trehalose. Both compounds were isolated and identified by nuclear magnetic resonance spectroscopy and mass spectrometry. A very sensitive regulation of the cell osmolytes was demonstrated in exponentially growing cultures. The intracellular levels of GG and trehalose increased 2x in response to a step change of medium osmolarity caused by 0.3 % NaCl. 1H NMR analysis of the cell extracts did not confirm the presence of additional osmolytes. GG is a S. caelestis metabolite commonly released from the cells; its concentration reached 3 g/L during the cultivation in a yeast extract-(NH4)2SO 4-glycerol medium. This is the first report on the occurrence of the ionic osmolyte GG in the genus Streptomyces and on its free excretion to the medium.