AME 34:239-246(2004)  -  doi: 10.3354/ame034239

ABSTRACT: The marine Stilbonematinae (Nematoda) are known for their highly specific mutualistic association with thiotrophic ectosymbiotic bacteria. The mechanism mediating recognition and binding between symbionts and host was studied in 5 host species. When incubated with d-mannose and l-rhamnose the symbionts detached in 2 species, Laxus cosmopolitus and L. oneistus, most likely due to competitive interactions with sugars involved in the binding mechanism; 3 other species, Stilbonema maium, Eubostrichus topiarius and E. dianae, did not lose their bacteria during any tested sugar incubations. Incubations with lectins binding specifically to d-glucose/d-mannose (ConA, concanavalin agglutinin) and to d-mannose (NPA, Narcissus pseudonarcissus agglutinin) respectively, both in vivo and on ultrathin sections, confirmed that accessible d-mannose is located on the symbionts of L. cosmopolitus, but not on the host¹s surface. Our results showed an involvement of d-mannose and l-rhamnose residues of the bacterial surface in the attachment mechanism. We hypothesize that the recognition and binding of the environmentally transmitted symbionts in the 2 Laxus species, which harbor only 1 phylotype of symbiotic γ-proteobacterium each, is most probably mediated through a yet unknown mannose/rhamnose-specific lectin of host origin.

KEY WORDS: Stilbonematinae · Nematoda · Thiotrophic ectosymbionts · Symbiosis · Environmental transmission · Attachment · Recognition