LIPOPOLYSACCHARIDES OF POLYMYXIN-B-RESISTANT MUTANTS OF ESCHERICHIA-COLI ARE EXTENSIVELY SUBSTITUTED BY 2-AMINOETHYL PYROPHOSPHATE AND CONTAIN AMINOARABINOSE IN LIPID-A

Lipopolysaccharides (LPS) of two polymyxin-resistant (pmr) mutants and the corresponding parent strain of Escherichia coli were chemically a nalysed for composition and subjected to P-31-NWIR (nuclear magnetic r esonance) for assessment of phosphate substitution, Whereas the saccha ride portions, fatty acids, and phosphate contents were similar in wil d-type and pmr LPS, the latter contained two- to threefold higher amou nts of 2-aminoethanol, The pmr LPS also contained 4-amino-4-deoxy-L-ar abinopyranose (L-Ara(p)4N), which is normally not a component of E. co li LPS. This aminopentose has been assigned to be linked to the 4'-pho sphate of lipid A, Comparative P-31-NMR analysis of the de-O acylated LPS of the wild-type and pmr strains revealed that phosphate groups of the pmr LPS were mainly (71-79%) diphosphate diesters, which accounte d for only 20% in the wild-type LPS. Diphosphate monoesters were virtu ally nonexistent in the pmr LPS, whereas they accounted for 42% of all phosphates in wild-type LPS, In the lipid A of the pmr strains, the 4 '-phosphate was to a significant degree (35%) substituted by L-Ara(p)4 N, whereas in the wild-type LPS the L-Ara(p)N was absent, In the pmr l ipid A, 2-aminoethanol was completely substituting the glycosidic pyro phosphate but not the glycosidic monophosphate, forming a diphosphate diester linkage at this position in 40% of lipid A molecules, In the w ild-type LPS the glycosidic position of lipid A carried mostly unsubst ituted monophosphate and pyrophosphate. Thus the polymyxin resistance was shown to be associated, along with the esterification of the lipid A 4'-monophosphate by aminoarabinose, with extensive esterification o f diphosphates in LPS by 5-aminoethanol.