COMMON LINKS IN THE STRUCTURE AND CELLULAR-LOCALIZATION OF RHIZOBIUM CHITOLIPOOLIGOSACCHARIDES AND GENERAL RHIZOBIUM MEMBRANE PHOSPHOLIPID AND GLYCOLIPID COMPONENTS

Several common links between the structural chemistry of the chitolipo oligosaccharides of Rhizobium and the general rhizobial membrane lipid and lipopolysaccharide chemistry of these bacteria have been uncovere d. Aspects of common chemistry include sulfation, methylation, and the position and extent of fatty acyl chain unsaturation. We find that ba cteria which are known to synthesize sulfated chitolipooligosaccharide s (such as Rhizobium meliloti strains and the broad-host-range Rhizobi um species strain NGR234) also have sulfated lipopolysaccharides. Thei r common origins of sulfation have been demonstrated by using mutants which are known to be impaired in sulfating their chitolipooligosaccha rides. In such cases, there is a corresponding diminution or complete lack of sulfation of the lipopolysaccharides. The structural diversity of the fatty acids observed in the chitolipooligosaccharides is also observed in the other membrane lipids. For instance, the doubly unsatu rated fatty acids which are known to be predominant components of R. m eliloti chitolipooligosaccharides were also found in the usual phospho lipids and glycolipids. Also, the known functionalization of the chito lipooligosaccharides of R. sp. NGR234 by O- and N-methylation was also reflected in the lipopolysaccharide of this organism. The common stru ctural features of chitolipooligosaccharides. and membrane components are consistent with a substantial degree of biosynthetic overlap and a large degree of cellular, spatial overlap between these molecules. Th e latter aspect is clearly demonstrated here since we show that the ch itolipooligosaccharides are, in fact, normal membrane components of Rh izobium. This increases the importance of understanding the role of th e bacterial cell surface chemistry in the Rhizobium/legume symbiosis a nd developing a comprehensive understanding of the highly integrated m embrane lipid and glycolipid chemistry of Rhizobium.