Comparison of the function of L- and D-proline as compatible solute in Escherichia coli K-12 under high osmolarity

Abstract

We compared the function of L- and D-proline as compatible solute in Escherichia coli K-12 cells under high osmolarity. Growth of E. coli K-12 in a Davis minimal medium was inhibited at 0.5 M and 1 M NaCl, but it was recovered by the addition of L-proline. Glucose uptake was reduced with increase of external NaCI concentrations, but it was improved by the addition of L-proline. On the other hand, the addition of D-proline did not show the role of compatible solute although accumulated in cells. On the analysis of E. coli proline transporter mutants, difference of the affinity of proline transporters for D-proline was observed at PutP and ProP. These results presumed that the functional disorder of D-proline as compatible solute was caused by its structural feature in cells.