Structure of the peptidoglycan of E. coli BW25113, BW25113Δ5, and BW25113Δ5/pTRC99aΩycbB. (A) rp-HPLC profiles of muropeptides obtained by digestion of the peptidoglycan by muramidases. Muropeptides 1 to 14 and A have been assigned to specific peaks detected by the absorbance at 210 nm. Muropeptides B to F could not be assigned to any specific absorbance peaks due to their low abundance; mAU, absorbance units (103). (B) Identification of muropeptides in the main peaks by mass spectrometry. GMR, N-acetyl-glucosamine linked to reduced N-acetyl-muramic acid; GMA, N-acetyl-glucosamine linked to anhydro-N-acetyl-muramic acid; Tri, tripeptide l-Ala-d-iGlu-meso-DAP; Tri-Gly, tetrapeptide l-Ala-d-iGlu-meso-DAP-Gly; Tetra, tetrapeptide l-Ala-d-iGlu-meso-DAP-d-Ala. The type of cross-links (3-3 or 4-3) is indicated in parentheses for dimers and trimers.