Fig. 2. Structures of the lipid A regions of LPSs used in this study. The structure of the lipid A region of R. species Sin-1 is not completely determined but, as that from some other Rhizobiaceae (Bhat et al., 1994), it is devoid of phosphate, has 2-aminogluconate in place of glucosamine-1-phosphate, and contains the very long chain of 27-hydroxyoctacosanoic acid (27-OHC28:0) that may be ester-linked in the N-acyloxylacyl residue of the distal glucosamine unit (Basu et al., 1999). The lipid A regions of the LPSs from three strains of Legionella pneumophila (Zähringer et al., 1995; Kooistra et al., 2002a) are built upon the same structural model (two residues of 2,3-diaminoglucose substituted with one very long and five shorter fatty acids), with variations limited to the length or substituents of the fatty acid chains in positions 2 and 2': R₁=H or OH; R₂=OH or CH₃; n=18-22 (in strains CS338 and RC1), or n=16-18 (in strain 811).