Characterization of O-antigen polysaccharide backbone derived from nitric oxide-inducing Mesorhizobium loti MAFF 303099 lipopolysaccharide.

Mesorhizobium loti is a member of rhizobia and establishes nitrogen-fixing symbioses with several Lotus species. Recently, we reported that M. loti MAFF 303099 bacterial cells and their lipopolysaccharide (LPS) preparations are involved in the beginning of the symbiotic process by inducing transient nitric oxide (NO) production in the roots of L. japonicus. We subsequently found that both the polysaccharide (PS) part and the lipid A moiety in LPS are responsible for the NO induction. In this study, we elucidated the chemical structure of M. loti O-polysaccharide (OPS) in PS. PS was prepared by mild acid hydrolysis of M. loti LPS followed by gel filtration chromatography. OPS was subjected to hydrazine treatment to obtain deacylated PS (dPS). Chemical composition analysis, ethylation analysis, and NMR spectra revealed the chemical structure of the M. loti OPS backbone in dPS to be →2)-α-l-6dTalp-(1 → 3)-α-l-6dTalp-(1 → 2)-α-l-Rhap-(1 → 2)-α-l-6dTalp-(1 → 3)-α-l-6dTalp-(1 → 3)-α-l-Rhap-(1→.