EFFECT ON LIPOPOLYSACCHARIDE STRUCTURE OF AERATION DURING GROWTH OF APLUM ISOLATE OF PSEUDOMONAS-SYRINGAE PV MORSPRUNORUM

The composition of lipopolysaccharide (LPS) extracted with aqueous phe nol from a virulent English plum isolate of Pseudomonas syringae pv. m orsprunorum varied according to the partial pressure of oxygen (pO(2)) in the culture medium at the time of harvest. When pO(2) was low, the organism grew slowly and produced smooth LPS bearing rhamnan sidechai ns. As pO(2) was raised. the rate of growth increased and smooth LPS w as replaced by a rough species deficient in rhamnose, which co-extract ed with a D-glucan. Organization of rhamnose and glucose into separate polymers was shown by the selective susceptibility of the rhamnose-co ntaining polymer to hydrolysis by rhamnanase of the phage A7. By methy lation analysis, GC-MS, and H-1- and C-13-NMR spectroscopy, the glucan was shown to consist of all alpha(1 --> 4)-linked residues with alpha (1 --> 4,6)-branch points and non-reducing terminal residues in the ap proximate ratio 4:1:1, resembling glycogen in composition. A glucan wh ich co-extracted with LPS using phenol/water from an avirulent plum is olate that was resistant to lysis by phages A1 and A7 was shown by met hylation analysis to have a similar structure. Whether the effect on L PS composition was due directly to pO(2), or was dependent on the rate of growth, has not been established. It is suggested that, because ep iphytic growth would entail exposure to high pO(2), English plum isola tes growing on the surfaces of host plants might be unable to produce smooth LPS. Since cell surface composition affects virulence in plant- pathogenic pseudomonads, this effect could account for the observed fa ilure of the English plum isolates to enter the host via leaf scars.