FIG 1.

A. baumannii LpxO 2-hydroxylates lipid A. (A) A. baumannii encodes an LpxO homolog with 62% and 59% sequence similarity to K. pneumoniae and S. enterica serovar Typhimurium LpxO, respectively. Shown are negative-ion MALDI-TOF mass spectrometry spectra of lipid A purified from A. baumannii ATCC 17978 (B), A. baumannii ΔlpxO mutant (ΔlpxO) (C), and A. baumannii ΔlpxO::Tn7lpxO mutant (ΔlpxO::Tn7lpxO) (D). Data represent the mass-to-charge ratios (m/z) of each lipid A species detected and are representative of three extractions. (E) Proposed lipid A structures of the species produced by wild-type A. baumannii based on previous publications (7–11).