Evidence for feedback (trans) regulation of, and two systems for, glycine betaine transport by Staphylococcus aureus

Previous reports are in conflict as to the number of transport systems for glycine betaine in Staphylococcus aureus. Cells grown in complex medium exhibited a single transport system of moderate affinity. Cells grown in defined medium in the absence of glycine betaine showed a high affinity and a low affinity transport system. Cells grown in the presence of glycine betaine in the presence of osmotic stress in either complex or defined media accumulated large pools of internal glycine betaine. Smaller, but still significant, amounts of glycine betaine were accumulated by cells grown in its presence in either complex or defined media in the absence of osmotic stress. Cells grown in defined medium in the presence of glycine betaine in the presence or absence of osmotic stress showed lower rates of glycine betaine transport than cells grown in its absence. This suggests that glycine betaine transport is subject to feedback or trans inhibition by internal glycine betaine. This can explain the difference in observed kinetics in cells grown in complex or defined media, the high affinity system being predominantly inhibited in cells grown in complex medium.