Figure 2

Chemical changes in the cell walls of mreB mutant cells. (a) Relative quantification of charges at the cell surface of wild–type, ∆mreB and ∆tagO cells. Charges detected by XPS expressed as molar percentage. Cells were grown in LB medium with or without added Mg²⁺ as indicated. % Total positive charges = % total metals (Na + K + 2·Ca + 2·Mg) + % protonated amines (Nprot). % Total negative charges = % phosphorus . The average of two independent sets of experiments (Table S2) is presented for each condition (see Methods for details of the quantifications). (b–e) Percentage of amidated muropeptides (b), deacetylation of muropeptides (c), DD-endopeptidase products (d) and DL-endopeptidase products (e) in wild-type and ∆mreB mutants grown with and without excess magnesium. Percentages were calculated from the quantification of the UPLC peaks (see Materials and Methods). Muropeptide composition analysis were performed in duplicate for all strains. ds refers to disaccharide (GlcNAc-MurNAc) and is followed by numbers which indicate the peptide length, as follows: 2 = dipeptide (L-Ala-D-iGlu), 3 = tripeptide (L-Ala-D-iGlu-mDAP). (a) = amidation. (-Ac) = missing acetyl group.