RHIZOBIUM-LEGUMINOSARUM BV TRIFOLII PRODUCES LIPO-CHITIN OLIGOSACCHARIDES WITH NODE-DEPENDENT HIGHLY UNSATURATED FATTY ACYL MOIETIES - AN ELECTROSPRAY-IONIZATION AND COLLISION-INDUCED DISSOCIATION TANDEM MASS-SPECTROMETRIC STUDY

The lipo-chitin oligosaccharides (LCO) or nodulation factors synthesiz ed by Rhizobium leguminosarum bv. trifolii were analyzed using positiv e mode fast atom bombardment and positive and negative mode electrospr ay ionization mass spectrometry. From their mass spectrometric behavio r it is clearly possible to distinguish between the [M + Na](+) pseudo molecular ion of the nodE-independent molecule IV(C18:1,Ac) and the [M + H](+) pseudomolecular ion of the nodE-dependent molecule IV(C20:4,A c), although they both have the same mass value. The results unequivoc ally show that the bacterial strain investigated produces nodE-depende nt LCOs with highly unsaturated fatty acyl moieties. We further demons trate that the interpretation of the mass spectrometric data by Philip -Hollingsworth et al. (Philip-Hollingsworth, S., Orgambide, G. G., Bra dford, J. J., Smith, D. K., Hollingsworth, R. I., and Dazzo, F. B. (19 95) J. Biol. Chem. 270, 20968) is incorrect and that their data do not contradict our hypothesis that the nodE gene determines the host spec ificity of R. leguminosarum bv. trifolii.