Glycine betaine transport in the obligate halophilic archaeon Methanohalophilus portucalensis

Transport of the osmoprotectant glycine betaine was investigated using the glycine betaine-synthesizing microbe Methanohalophilus portucalensis (strai n FDF1), since solute uptake for this class of obligate halophilic methanog enic Archaea has not been examined. Betaine uptake followed a Michaelis-Men ten relationship,,vith an observed K-t of 23 mu M and a V-max of 8 nmol per min per mg of protein. The transport system was highly specific for betain e: choline, proline, and dimethylglycine did not significantly compete for [C-14]betaine uptake. The proton-conducting uncoupler 2,4-dinitrophenol and the ATPase inhibitor N,N-dicyclohexylcarbodiimide both inhibited glycine b etaine uptake. Growth of cells in the presence of 500 mu M betaine resulted in faster cell growth due to the suppression of the de novo synthesis of t he other compatible solutes, alpha-glutamate, beta-glutamine, and N-e-acety l-beta-lysine. These investigations demonstrate that this model halophilic methanogen, M. portucalensis strain FDF1, possesses a high-affinity and hig hly specific betaine transport system that allows it to accumulate this osm oprotectant from the environment in lien of synthesizing this or other osmo protectants under high-salt growth conditions.