Biosynthesis of the wall neutral polysaccharide in Bacillus cereus AHU 1356.

The pathway for the biosynthesis of a cell wall polysaccharide, composed of glucosamine, mannosamine, galactosamine and glucose in a molar ratio of 4:1:1:1, was studied with a membrane system from Bacillus cereus AHU 1356. In this system a glycolipid characterized as GalNAc(alpha 1----4)ManNAc(beta 1----4)GlcNAc-PP-undecaprenol was formed from GlcNAc-PP-undecaprenol by sequential transfer of N-acetylmannosamine and N-acetylgalactosamine residues from UDP-ManNAc and UDP-GalNAc respectively. An additional N-acetylglucosamine residue and a glucose residue were individually transferred from their UDP derivatives to the trisaccharide-linked lipid with the formation of tetrasaccharide-linked lipids, which seem to serve as intermediates in the polysaccharide synthesis. Incubation of membranes with the trisaccharide-linked lipid even in the absence of sugar-linked nucleotides led to the formation of polysaccharide. These results, together with the data on Smith degradation of the synthesized polysaccharide, indicate that the repeating trisaccharide units of the main chain of the polysaccharide arise from the GalNAc-ManNAc-GlcNAc moiety of the glycolipid intermediates and that the sugar residues in the lateral branches of the polymer are at least partly introduced through oligosaccharide-linked lipid intermediates. In addition, the structure of native polysaccharide was re-examined, and the presence of the disaccharide sequence ManNAc(beta 1----4)GlcNAc in the polysaccharide chain was confirmed.