Genetic and chemical characterization of a mutant that disrupts synthesis of the lipopolysaccharide core tetrasaccharide in Rhizobium leguminosarum

A 2-kb region that complements the Tn5-derived lipopolysaccharide (LPS) rough mutant Rhizobium leguminosarum RU301 was sequenced, Two open reading frames (ORFs) were identified. The first ORF (lpcA) is homologous to a family of bacterial sugar transferases involved in LPS core tetrasaccharide biosynthesis, ORF2 (lpcB), in which Tn5 transposed, has no significant homology to any DNA in the GenBank-EMBL databases, Chemical characterization of LPS produced by strain RU301 demonstrated that the 3-deoxy-Dmanno-2-octulosonic acid (Kdo) residue which normally attaches the core tetrasaccharide to the O chain was missing, suggesting that lpcB may encode a CMP-Kdo:LPS Kdo transferase.