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

Attachment mechanism in a highly specific association between ectosymbiotic bacteria and marine nematodes

Andrea D. Nussbaumer1,*, Monika Bright1, Christian Baranyi2, Christian J. Beisser3, Jörg A. Ott1

1Section of Marine Biology, Institute of Ecology and Conservation Biology,
2Section of Limnology, Institute of Ecology and Conservation Biology, and
3Section of Comparative Anatomy and Morphology, Institute of Zoology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

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

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