Contribution of 252Cf-plasma desorption mass spectrometry to structural analysis of lipids A:: examples of non-conservatism in lipid A structure

The great majority of lipids A studied so far have the enterobacterial lipid A-type skeleton: a bisphosphorylated glucosamine disaccharide, with fatty acids amidating the 2 amino groups and esterifying the C3 and C3' positions. Differences between these lipids A occur in the nature and localization of the fatty acids. Such differences have been put forward as a possible taxonomic tool. It is now relatively easy to determine these differences using plasma desorption mass spectrometry (PDMS) if one knows the overall composition of the pure, native lipids A. We have used this technique to compare the lipids A of 2 or more species of several bacterial genera and found considerable conservatism within genera and sometimes between closely related genera (Salmonella and Escherichia). An exception was Bordetella of which different species varied in the nature and/or the localization of their fatty acids. B. parapertussis, like B. pertussis, had a single C10OH but at a different location, and quite unusually had a non-hydroxylated fatty acid (C-16) directly esterifying glucosamine I. On the other hand, 2 strains of B. bronchiseptica had a C12OH in place of the C10OH of B. pertussis, whereas a third strain replaced the C12OH by a C-12, again a primary non-hydroxylated fatty acid. PDMS has allowed us to conclude that the combined pattern of fatty acids in lipids A is not a reliable taxonomic tool.