Mechanisms of partner adhesion in a marine ectosymbiosis
 
Silvia Bulgheresi, Irma Schabussova, Andrea Nussbaumer and Joerg Ott,
University of Vienna, Austria
 

Marine associations in which bacteria are located at the interface between their invertebrate host and the environment represent ideal experimental subjects, if we want to understand how symbioses can be established. Laxus oneistus (Desmodoridae, Stilbonematinae) is a free-living nematode characterized by an horizontally transmitted mono-specific bacterial coat covering all but the anterior part of its surface. It feeds on its symbionts and alternatively supplies them with sulphide and oxygen by migrating through the chemocline. Searching for molecules involved in partners adhesion, we found that bacteria detach from Laxus by mannose incubation and focused on the search for Laxus mannose-specific lectins. Nematodes protein extracts were subjected to mannose affinity chromatography and the resulting fractions where analyzed by SDS-PAGE and silver staining. This led to the identification of two abundantly expressed lectins of molecular weights comprised between 75 and 50 KD, provisionally called Lo-L1 and Lo-L2. Corresponding tryptic digests are currently being subjected to MALDI Mass Spectrometry in order to gain protein sequence information. In parallel, antibodies against a Toxocara canis C-type mannose binding lectin (Tc-CTL-1) were tested on fixed Laxus individuals. Specific immunofluorescence of the bacteria-associated region of their surface, suggests C-type lectins might be required for symbionts attachment. Intriguingly, antibodies against Tc-CTL-1 were also able to cross-react with Lo-L1 and L2 on Western blots. Whether the latter are Tc-CTL-1 homologues or not, the cloning of their cDNAs promises to enhance our understanding of how animals and bacteria establish healthy relationships.