BIOCHEMICAL-CHARACTERIZATION AND AGGLUTINATING PROPERTIES OF XENORHABDUS-NEMATOPHILUS F1 FIMBRIAE

Xenorhabdus spp., entomopathogenic bacteria symbiotically associated w ith nematodes of the family Steinernematidae, occur spontaneously ip t wo phases. Only the phase I variants of Xenorhabdus nematophilus F1 ex pressed fimbriae when the bacteria were grown on a solid medium (nutri ent agar; 24 and 48 h of growth). These appendages were purified and c haracterized. They were rigid, with a diameter of 6.4 +/- 0.3 nm, and were composed of 16-kDa pilin subunits. The latter were synthesized an d assembled during the first 24 h of growth. Phase II variants of X. n ematophilus did not possess fimbriae and apparently did not synthesize pilin. Phase I variants of X. nematophilus have an agglutinating acti vity with sheep, rabbit, and human erythrocytes and with hemocytes of the insect Galleria mellonella. The purified fimbriae agglutinated she ep and rabbit erythrocytes. The hemagglutination by bacteria and purif ied fimbriae was mannose resistant and was inhibited by porcine gastri c mucin and N-acetyl-lactosamine. The last sugar seems to be a specifi c inhibitor of hemagglutination by X. nematophilus.