Transport of glycine betaine in the extremely haloalkaliphilic sulphur bacterium Ectothiorhodospira halochloris

The effect of osmotic stress on the transport of the compatible solute glycine betaine was examined in Ectothiorhodospira halochloris, an extremely haloalkaliphilic, phototrophic sulphur bacterium. Kinetic data indicated that E. halochloris possesses an active transport system for glycine betaine which is saturable and exhibits Michaelis-Menten kinetics. Experiments with chloramphenicol-treated cells (50 μg per ml of cell suspension) indicated that the transport system is constitutive and might be activated by a change in osmotic pressure. The uncouplers carbonyl cyanide m-chlorophenylhydrazone (CCCP) and carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (CCFP) totally blocked uptake at concentrations of 25 μM and 100 μM, respectively. The system was insensitive to the cytochrome oxidase inhibitor sodium azide (1 mM), the respiratory chain inhibitor potassium cyanide (1 mM) and the glycolysis inhibitor iodoacetate (1 mM). The ionophore nigericin (50 μM) had the greatest inhibitory effect, completely abolishing uptake, while monensin (100 μM) caused 80% inhibition. Glycine betaine transport possessed considerable structural specifity: proline betaine was the most effective competitor and trigonelline and dimethylglycine exerted inhibition to a lesser extent. Transport in the dark was at a greatly reduced rate. These results collectively implied that the specific transport of glycine betaine might be driven by the electrochemical proton gradient generated by anaerobic photosynthesis.