Modulation of Peptidoglycan Synthesis by Recycled Cell Wall Tetrapeptides

Abstract

The bacterial cell wall is made of peptidoglycan (PG), a polymer that is essential for maintenance of cell shape and survival. During growth, bacteria remodel their PG, releasing fragments that are predominantly re-internalized and recycled. Here, we show that Vibrio cholerae recycles PG fragments modified with non-canonical D-amino acids (NCDAA), which lead to the accumulation of cytosolic PG tetrapeptides. We demonstrate that accumulation of recycled tetrapeptides has two regulatory consequences for the cell wall: reduction of D,D-cross-linkage and reduction of PG synthesis. We have demonstrated that L,D-carboxypeptidases from five different species show a preferential activity for substrates containing canonical (D-Alanine) vs. non-canonical (D-Methionine) D-amino acids, suggesting that accumulation of recycled tetrapeptides in NCDAA-rich environments is a widespread phenomenon. Collectively, this work highlights the role of NCDAA in interspecies PG modulation and reveals an unnoticed link between PG recycling and synthesis to promote optimal cell wall assembly and composition.