Uptake of cell wall peptides by Salmonella typhimurium and Escherichia coli

During bacterial growth, cell wall peptides are released from the murein and reused for the synthesis of new cell wall material. Mutants defective in peptide transport were unable to reutilize cell wall peptides, demonstrating that these peptides are taken up intact into the cytoplasm prior to reincorporation into murein. Furthermore, cell wall peptide recycling was shown to play an important physiological role; peptide transport mutants which were unable to recycle these peptides showed growth defects under appropriate conditions. Using mutants specifically defective in each of the three peptide transport systems, we showed that the uptake of cell wall peptides was mediated solely by the oligopeptide permease (Opp) and that neither the dipeptide permease (Dpp) nor the tripeptide permease (Tpp) played a significant role in this process. Our data indicate that the periplasmic oligopeptide-binding protein has more than one substrate-binding site, each with different though overlapping specificities.