OSMOTIC ADAPTATION IN BREVIBACTERIUM LINENS - DIFFERENTIAL EFFECT OF PROLINE AND GLYCINE BETAINE ON CYTOPLASMIC OSMOLYTE POOL

In the coryneform Brevibacterium linens, ectoine constitutes the major intracellular solute accumulated under elevated medium osmolarity. He re we report that exogenously supplied proline, choline, glycine betai ne, and even ectoine, protected bacterial cells against deleterious ef fects of a hyperosmotic constraint (i.e. 1.5 M NaCl). In all cases, a significant improvement of growth was observed; in parallel, intracell ular osmolyte pools composed mainly of glutamate and ectoine substanti ally increased, either with added glycine betaine (under Limiting supp ly) or with proline. However, these two osmoprotectants behaved differ ently: glycine betaine acted as a genuine osmoprotectant, whereas prol ine was accumulated only transiently and participated actively in the biosynthesis of glutamate, ectoine, and trehalose. The strategy develo ped by B. linens cells allows the proposal of a novel role for proline in the osmoprotection process through its conversion to the apparentl y preferred endogenous osmolyte ectoine.