GLYCINE BETAINE TRANSPORT BY STAPHYLOCOCCUS-AUREUS - EVIDENCE FOR FEEDBACK-REGULATION OF THE ACTIVITY OF THE 2 TRANSPORT-SYSTEMS

The regulation of glycine betaine accumulation by Staphylococcus aureu s was investigated. The accumulation of glycine betaine was regulated by the osmotic pressure of the medium and the tow affinity transport s ystem played the major role in this regulation. Mutants were isolated that lack the row affinity, osmotically activated glycine betaine/prol ine transport system. Such mutants accumulated glycine betaine via the high affinity system but the glycine betaine pool was smaller and res ponded poorly to osmotic pressure changes. The regulation of glycine b etaine transport has revealed that at the steady state net influx is r educed and that this is achieved by inhibition of both the low affinit y and the high affinity transport systems. Cells pre-loaded with glyci ne betaine exhibited a reduced V-max for both systems:the low affinity system was reduced in activity fivefold and the high affinity system was reduced 10-fold and became virtually undetectable. Although glycin e betaine transport at the steady state is reduced, retention of the c ompatible solute is an active process since addition of an uncoupler p rovokes rapid release of the accumulated material. These data suggest that feedback regulation of the activity of the uptake systems is a ma jor mechanism for controlling the level of compatible solute accumulat ion.