Figure 5.

Negative-ion MALDI MS/MS spectrum of the precursor ion at m/z 1579.8, a representative ion peak of the cluster matching with tetra-acylated lipid A species from E. vietnamensis KMM 6221^T. The assignment of main fragments is indicated. The proposed structure for the lipid A species is reported in the inset. In this case, the representation of 15:0(3-OH) in its branching form is tentative. Since both the phosphate group and the HexA unit may be candidates to hold the charge, the proposed structure has been depicted carrying two negative charges for information purposes only.