The effect of NaCl on the growth of a Halomonas species: accumulation and utilization of compatible solutes

Abstract

The effect of NaCl on growth and compatible solute utilization was investigated in a Halomonas species. Growth of Halomonas was observed in medium of low osmolarity (high water activity) when only 01 mM Na⁺ was present. However, lowering the water activity, by addition of KCl or sucrose, inhibited growth in this low-Na⁺ medium, but growth could be restored by the addition of NaCl. The bacterium could grow on glucose as the sole carbon source in up to 355 M NaCl and was shown also to metabolize glycine betaine. However NaCl concentrations greater than 2 M inhibited growth when glycine betaine was the sole carbon source. Glycine betaine was transported into the cells by a process stimulated by NaCl irrespective of whether the carbon source was glucose or glycine betaine. Cytoplasmic levels of glycine betaine were monitored throughout the growth cycle in 2 M NaCl medium with glycine betaine as sole carbon source. As the culture aged, glycine betaine was increasingly replaced by the tetrahydropyrimidine ectoine as the major cytoplasmic solute. The increased sensitivity to high NaCl concentrations when grown on glycine betaine may be due to the glycine betaine catabolic pathway enzymes being inhibited by the increasing external solute concentration.

Keywords: Halomonas; compatible solutes; glycine betaine; sodium.