Variation at the common polysaccharide antigen locus drives lipopolysaccharide diversity within the <i>Pseudomonas syringae</i> species complex

<jats:title>Summary</jats:title><jats:p>The common polysaccharide antigen (CPA) of the lipopolysaccharide (LPS) from <jats:italic>Pseudomonas syringae</jats:italic> is highly variable, but the genetic basis for this is poorly understood. We have characterized the CPA locus from <jats:italic>P. syringae</jats:italic> pv. <jats:italic>actinidiae</jats:italic> (<jats:italic>Psa</jats:italic>). This locus has genes for <jats:sc>l</jats:sc>‐ and <jats:sc>d</jats:sc>‐rhamnose biosynthesis and an operon coding for ABC transporter subunits, a bifunctional glycosyltransferase and an <jats:sc>o</jats:sc>‐methyltransferase. This operon is predicted to have a role in the transport, elongation and termination of the CPA oligosaccharide and is referred to as the TET operon. Two alleles of the TET operon were present in different biovars (BV) of <jats:italic>Psa</jats:italic> and lineages of the closely related pathovar <jats:italic>P. syringae</jats:italic> pv. <jats:italic>actinidifoliorum</jats:italic>. This allelic variation was reflected in the electrophoretic properties of purified LPS from the different isolates. Gene knockout of the TET operon allele from BV1 and replacement with that from BV3, demonstrated the link between the genetic locus and the biochemical properties of the LPS molecules in <jats:italic>Psa</jats:italic>. Sequence analysis of the TET operon from a range of <jats:italic>P. syringae</jats:italic> and <jats:italic>P. viridiflava</jats:italic> isolates displayed a phylogenetic history incongruent with core gene phylogeny but correlates with previously reported tailocin sensitivity, suggesting a functional relationship between LPS structure and tailocin susceptibility.</jats:p>