L-carnitine metabolization and osmotic stress response in Escherichia coli.

Growth of Escherichia coli 044 K 74 in liquid medium of raised osmotic strength was stimulated by exogenous L-carnitine, crotonobetaine and gamma-butyrobetaine, respectively. L-Carnitine was accumulated within the cells in dependence on the salt concentration of the media. Osmotic stress during aerobic or anaerobic growth with glucose triggered the L-carnitine uptake in E. coli 044 K 74 whereas L-carnitine uptake by cells of this organism grown anaerobically on glycerol/fumarate was only slightly modified. Synthesis of the enzymes metabolizing L-carnitine to gamma-butyrobetaine in glycerol/fumarate growing bacteria was found to be completely repressed by high NaCl-concentrations. Together, these results indicate that most likely the L-carnitine metabolization sequence does not play a role in osmoregulation in E. coli 044 K 74.