Inactivation of prb has a strong negative effect on osmoprotection by PB and glycine betaine. Cells were grown in MCAA medium with 0.6 M NaCl in the presence of 1 mM PB (A) or 1 mM glycine betaine (GB) (B). Strains used were Rm1021 (wild-type) (⧫), S7 (prb) (•), RmUNA369 (betS) (○), and RmUNA370 (prbB betS) (▴). Growth of RmUNA370 in MCAA medium with 0.6 M NaCl (without osmoprotectant) is also shown (▵). The results are means of three independent cultures, and standard deviations did not exceed 5%. OD, optical density.