IDENTIFICATION OF ORGANIC SOLUTES ACCUMULATED BY PURPLE AND GREEN SULFUR BACTERIA DURING OSMOTIC-STRESS USING NATURAL-ABUNDANCE C-13 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Natural abundance C-13 NMR spectroscopy has identified sucrose and tre halose as the principle compatible solutes accumulated by non-halophil ic purple and green sulphur bacteria respectively, in response to osmo tic stress. Synthesis of glycine betaine as a compatible solute was ra re in non-halophilic phototrophic sulphur bacteria and appears to be l imited almost exclusively to halotolerant isolates, although all isola tes tested were able to accumulate exogenous glycine betaine from the growth medium in response to osmotic stress. These data support the hy pothesis that the degree of halotolerance of a microorganism may be du e, at least in part, to the metabolic effects of the compatible solute (s) accumulated.