In vitro synthesis of a lipid-linked acetylated and pyruvilated oligosaccharide in Rhizobium trifolii.

EDTA-treated Rhizobium trifolii cells (strain NA30) incorporate radioactivity from (14C) labeled UDP-Clc, UDP-ClcA, Acetyl-Coa and/or phosphoenol pyruvate into chloroform: methanol: water (1:2:0.3) extracts. The incorporation products have properties of prenyl-phospho-sugars; mild alkaline hydrolysis of these extracts produce cyclic phosphate esters suggesting the presence of a diphosphate bridge, and mild acid or catalytic reduction-alkaline phosphatase treatments release four main components a, b, c and d, as judged by paper electrophoresis and chromatography and gel filtration studies. The four components can be obtained (14C)acetyl-labeled, but only compound c and to a lesser degree compound b can be (14C)pyruvate-labeled. For the exopolysaccharide produced by this strain the following repeating unit has been proposed (Robertsen et al. (1981), Plant Physiol. 67, 389-400): (Formula: see text). The results obtained suggest that the octasaccharide repeating unit (compound a) with one (compound b) or two (compound c) ketal pyruvate residues are assembled on a lipid acceptor. All these compounds are assumed to be intermediates in the biosynthesis of R. trifolii exopolysaccharide.