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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 4637

Andrea D. Nussbaumer, Monika Bright, Christian Baranyi, Christian J. Beisser, and Jorg A. Ott; Attachment mechanism in a highly specific association between ectosymbiotic bacteria and marine nematodes. Aquatic Microbial Ecology 34:239-246, 2004

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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 host's 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 gamma-proteobacterium each, is most probably mediated through a yet unknown mannose/rhamnose-specific lectin of host origin.