Fig. 2.

Altered lipid A composition, lack of 4′-phosphatase activity, and polymyxin hypersensitivity of the F. novicida lpxF mutant. (A) Thin-layer chromatography of F. novicida lipids labeled uniformly with ³²P and extracted by using a two-phase Bligh–Dyer system (16, 37). Samples containing ≈10,000 cpm were spotted in each lane. The plate was developed with chloroform/pyridine/88% formic acid/water (50:50:16:5, vol/vol), and the lipids were detected with a PhosphorImager. Most of the lipid A found in F. novicida is not linked to LPS (12), possibly because of the presence of an unusual Kdo-cleaving activity (37). Therefore, most of the lipid A of F. novicida is extracted directly with chloroform/methanol, together with the glycerophospholipids (12). The structure of compound A4 is shown in Fig. 1C. It accumulates in the lpxF mutant, whereas A1 and A2 disappear. (B) Absence of 4′-phosphatase activity in membranes of XWK4. (C) Kanamycin resistance and polymyxin hypersensitivity of mutant XWK4.