Immunochemical characterization and taxonomic evaluation of the O polysaccharides of the lipopolysaccharides of Pseudomonas syringae serogroup O1 strains

The O polysaccharide (OPS) of the lipopolysaccharide (LPS) of Pseudomonas s yringae pv. atrofaciens IMV 7836 and some other strains that are classified in serogroup O1 was shown to be a novel linear alpha-D-rhamnan with the te trasaccharide O repeat -->3)-alpha-D-Rhap- (1-->3)-alpha-D-Rhap-(1-->2)-alp ha-D-Rhap-(1--> (chemotype 1A). The same alpha-D-rhamnan serves as the back bone in branched OPSs with lateral (alpha 1-->3)-linked D-Rhap, (beta 1-->4 )-Iinked D-GlcpNAc, and (alpha 1-->4)-linked D-Fucf residues (chemotypes 1B , 1C, and 1D, respectively). Strains of chemotype 1C demonstrated variation s resulting in a decrease of the degree of substitution of the backbone 1A with the lateral D-GlcNAc residue (chemotype 1C-1A), which may be described as branched regular ---> branched irregular --> linear OPS structure alter ations (1C--->1C-1A --> 1A). Based on serological data, chemotype 1D was su ggested to undergo a 1D ---> 1D-1A alteration, whereas chemotype 1B showed no alteration. A number of OPS backbone-specific monoclonal antibodies (MAb s), Ps(1-2)a, Ps(1-2)a(1), Ps1a, Ps1a(1), and Ps1a(2), as well as MAbs Ps1b , Ps1c, Ps1c(1), Ps1d, Ps(1-2)d, and Ps(1-2)d(1) specific to epitopes relat ed to the lateral sugar substituents of the OPSs, were produced against P. syringae serogroup O1 strains. By using MAbs, some specific epitopes were i nferred, serogroup O1 strains were serotyped in more detail, and thus, the serological classification scheme of P. syringae aas improved. Screening wi th MAbs of about 800 strains representing ail 56 known P. syringae pathovar s showed that the strains classified in serogroup O1 were found among 15 pa thovars and the strains with the linear OPSs of chemotype 1A were found amo ng 9 of the 15 pathovars. A possible role for the LPS of P. syringae and re lated pseudomonads as a phylogenetic marker is discussed.