Identification of trehalose and glycine betaine as compatible solutes in the moderately halophilic sulfate reducing bacterium, Desulfovibrio halophilus

Abstract

Increasing NaCl concentrations in the growth medium inhibited the growth of Desulfovibrio halophilus due to both an increase in the lag phase of growth and a reduction in the specific growth rate. Addition of 1 mM glycine betaine to the growth medium partially relieved this inhibition. Natural abundance 13C nuclear magnetic resonance spectroscopy identified the disaccharide α-α trehalose and glycine betaine as the major organic solutes accumulated by D. halophilus during growth in mineral salts medium and mineral salts medium supplemented with 1 mM glycine betaine, respectively. The presence of a weak glycine betaine transport system was confirmed by following the accumulation of [methyl-14C]glycine betaine during osmotic upshock. In the absence of exogenous glycine betaine the intracellular trehalose concentration of D. halophilus was dependent upon the osmolarity of the growth medium, with a maximum concentration of 8.3 µmol trehalose mg protein−1 recorded in cultures grown in the presence of 15% w/v NaCl. Intracellular K+ concentrations were also dependent upon the osmolarity of the growth medium over the range 3–9% w/v NaCl, but showed little further increase at higher NaCl concentrations.