FIG. 2.

Proline becomes limiting to the growth of E. coli NCIMB 10214 at high osmolarity in the presence of peptone. (a) Growth stimulation by peptone and proline in the following: 0.5 M NaCl (○); 0.5 M NaCl plus 0.5% (wt/vol) peptone (▴); 0.5 M NaCl plus 1 mM proline (●); and 0.5 M NaCl plus 0.5% peptone plus 1 mM proline (■). (b) Extracellular free proline measured in cultures growing in the presence of peptone. Samples were taken when the culture reached the OD₆₅₀s indicated, and amino acid analyses were performed exactly as described in Materials and Methods. The asterisk represents undetectable levels. (c) Composite figure of the intracellular (filled bars) and extracellular (hatched bars) concentrations of free proline in cultures growing in the presence of peptone, at the OD₆₅₀s indicated.