S19.1 Structural analysis of the endotoxically active lipid a component of the halophilic bacteriumRhodospirillum salinarum

The structural elucidation of lipid A, isolated from the cell wall lipopolysaccharide of Rhodospirillum salinarum, by chemical methods including" laser desorption mass spectrometry, revealed that we were dealing with a mixed lipid A-type (1) being composed of three different 1,4'-bisphosphorylated /3(1 6)-linked backbone hexosaminyl-hexosamine-disaccharides, namely of GleN GleN, 2,3-diamino-2,3-dideoxy-DG l c (DAG)-DAG, and D A G G l e N . The latter mentioned hybrid type, i.e. the 2,3-diamino-2,3-dideoxy-/3-D-glucopyranosyl-(1 6)-o-glucosamine disaccharide was hitherto reported only once by Moran et al. (2) from LPS of the serotype 0 :2 of the pathogenic Gram-negative species Campylobacterjejuni. In contrast to the latter, the lipid A of R. salinarum contained preferentially 3-OH-14:0 and 3-OH18:0 (molar ratio about 1:4) as amide-linked, and 18:1 and 19:1 (molar ratio about 1:1) as ester-linked fatty acids. The mass spectra of the liberated acyl-oxyacyl residues proved the concomitant presence of 3-O-(19:1)-14:0 and 3-O-(18:1)-18:0 as the predominant amide-linked diesters in this lipid A. The glycosidically, as well as the ester-linked phosphate groups, were not substituted by ETN, P-ETN, or by 4-amino-4-deoxyL-arabinose, in contrast to most enterobacterial lipid As. LPS of R. salinarum showed a lethality (in C57Bl10 SCSNmice) in a range of 1 /10 -1 /100 from that reported for Salmonella abortus equi LPS (M. Freudenberg and H. Rau, unpublished results). This lower toxicity might possibly be due to the presence of a smaller extent and to the unusual nature (longer-chained) of the ester-linked fatty acids. (1) J. Weckesser and H. Mayer. FEMS MicrobioL Rev., 54 (1988) 143154. (2) A. P. Moran et al. J. Bacteriol., 173 (1991) 618-626.