Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
The first studies of the 16S rRNA gene diversity of the bacterial symbionts found in lucinid clams did not clarify how symbiotic associations had evolved in this group. Indeed, although species-specific associations deriving from a putative ancestral symbiotic association have been described (coevolution scenario), associations between the same bacterial species and various host species (opportunistic scenario) have also been described. Here, we carried out a comparative molecular analysis of hosts, based on 18S and 28S rRNA gene sequences, and of symbionts, based on 16S rRNA gene sequences, to determine as to which evolutionary scenario led to modern lucinid/symbiont associations. For all sequences analyzed, we found only three bacterial symbiont species, two of which are harbored by lucinids colonizing mangrove swamps. The last symbiont is the most common and was found to be independent of biotope or depth. Another interesting feature is the similarity of ctenidial organization of lucinids from the Philippines to those described previously, with the exception that two bacterial morphotypes were observed in two different species (Gloverina rectangularis and Myrtea flabelliformis). Thus, there is apparently no specific association between Lucinidae and their symbionts, the association taking place according to which bacterial species is present in the environment.
ISSN: 0168-6496

hal-00743766
https://hal.univ-antilles.fr/hal-00743766
DOI : 10.1111/j.1574-6941.2010.00989.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Background information. Marine nematodes belonging to the Stilbonematidae (Desmodoridae) family are described as living in obligatory association with sulfur-oxidizing chemoautotrophic ectosymbionts. The symbiotic bacteria carrying out this chemosynthesis should contain elemental sulfur in periplasmic granules as sulfur granules of chemoautotrophic endosymbionts described in various marine invertebrates. Results. Based on TEM analyses, extracellular bacteria surrounding Eubostrichus dianae possess these spherical periplasmic granules. Few investigative techniques can be used to identify elemental sulfur S8 such as EDXS (energy dispersive X-ray spectroscopy) and EELS (electron energy loss spectroscopy) associated with cryo-fixation of the sample to avoid sulfur loss. These techniques are time consuming, expensive and require technical skills. Raman microspectrometry applied to the analysis of E. dianae allowed us to detect elemental sulfur S8 and confirmed the location of these sulfur clusters in the bacterial coat. In the same way, Raman spectrometry was positively applied to the endosymbiotic bivalve Codakia orbicularis, suggesting that this technique can be used to characterize sulfur in ecto- as well as in endo-symbiotic sulfur-oxidizing bacteria. Conclusions. As Raman spectrometry can be used on living organisms (without preliminary fixation) without sample damage and preserving the molecular structure of the sulfur (denatured during chemical fixation) it represents a very well-adapted investigative tool for biologists. This technique therefore permits us to detect quickly and easily (in a few seconds and on entire living animals) the presence of sulfur compounds in the symbiotic nematode.
ISSN: 0248-4900

hal-00753017
https://hal.univ-antilles.fr/hal-00753017