Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The mangrove swamp environment constitutes a sulphide rich habitat harbouring some thioautotrophic organisms. The ciliate Zoothamnium niveum and the nematode Eubostrichus dianae, both known to live associated with bacterial sulphide-oxidizing ectosymbionts, were analysed as positive controls by Raman microspectrometry. The detection of the 3 Raman bands characteristic of elemental sulphur (S8) allows us to define a positive model of sulphide-oxidizing symbiotic invertebrates and by extrapolation, of thioautotrophic organisms. A fast screening using this tool was carried out on eukaryotic organisms such as hydrozoan, nematodes, annelids, copepods, and ciliate (Pseudovorticella sp.) and on free-living filamentous bacteria found on decomposing leaves in order to detect thioautotrophic organisms. The Raman microspectrometry permits us: (i) to reveal thioautotrophic metabolism of free-living bacteria (Beggiatoa sp.) and even for Archaea and (ii) to detect sulphide-oxidizing endosymbiotic and ectosymbiotic bacteria associated with the Bivalve Lucina pectinata and Pseudovorticella sp., respectively. Raman microspectrometry represents a fast, easy and non destructive technique which can be used on living organisms without constraints of sample size. The Raman analysis can also be completed by ultrastructural analysis (SEM, TEM) on the same sample.
ISSN: 0141-1136

hal-00715329
https://hal.univ-antilles.fr/hal-00715329
DOI : 10.1016/j.marenvres.2010.02.001

Éditeur(s) : HAL CCSD Royal Society, The
Résumé : International audience
Bathymodiolin mussels occur at hydrothermal vents and cold seeps, where they thrive thanks to symbiotic associations with chemotrophic bacteria. Closely related genera Idas and Adipicola are associated with organic falls, ecosystems that have been suggested as potential evolutionary 'stepping stones' in the colonization of deeper and more sulphide-rich environments. Such a scenario should result from specializations to given environments from species with larger ecological niches. This study provides molecular-based evidence for the existence of two mussel species found both on sunken wood and bones. Each species specifically harbours one bacterial phylotype corresponding to thioautotrophic bacteria related to other bathymodiolin symbionts. Phylogenetic patterns between hosts and symbionts are partially congruent. However, active endocytosis and occurrences of minor symbiont lineages within species which are not their usual host suggest an environmental or horizontal rather than strictly vertical transmission of symbionts. Although the bacteria are close relatives, their localization is intracellular in one mussel species and extracellular in the other, suggesting that habitat choice is independent of the symbiont localization. The variation of bacterial densities in host tissues is related to the substrate on which specimens were sampled and could explain the abilities of host species to adapt to various substrates.
ISSN: 0950-1193

hal-00755293
https://hal.univ-antilles.fr/hal-00755293
DOI : 10.1098/rspb.2008.1101

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a d13C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low d13C value can not be due to specific ingestion of 13C-depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by d13C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electronmicroscope views revealed the absence of bacterial endosymbionts. Energy-dispersive X-ray spectroscopy analysis detected low levels of sulfur (0.32%+-0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low d13C value of H. ruberrima can not be due to the presence of sulfur-oxidizing symbionts but more probably to the selective and exclusive consumption of free-living, sulfuroxidizing bacteria
ISSN: 0173-9565

hal-01253239
https://hal.archives-ouvertes.fr/hal-01253239
DOI : 10.1111/maec.12296

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
BackgroundSince the discovery of thioautotrophic bacterial symbiosis in the giant tubeworm Riftia pachyptila, there has been great impetus to investigate such partnerships in other invertebrates. In this study, we present the occurrence of a sulphur-oxidizing symbiosis in a metazoan belonging to the phylum Cnidaria in which this event has never been described previously.Methodology/Principal FindingsScanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) observations and Energy-dispersive X-ray spectroscopy (EDXs) analysis, were employed to unveil the presence of prokaryotes population bearing elemental sulphur granules, growing on the body surface of the metazoan. Phylogenetic assessments were also undertaken to identify this invertebrate and microorganisms in thiotrophic symbiosis. Our results showed the occurrence of a thiotrophic symbiosis in a cnidarian identified as Cladonema sp.Conclusions/SignificanceThis is the first report describing the occurrence of a sulphur-oxidizing symbiosis in a cnidarian. Furthermore, of the two adult morphologies, the polyp and medusa, this mutualistic association was found restricted to the polyp form of Cladonema sp.
ISSN: 1932-6203

hal-01203244
https://hal.univ-antilles.fr/hal-01203244
https://hal.univ-antilles.fr/hal-01203244/document
https://hal.univ-antilles.fr/hal-01203244/file/Plos%20Cladonema%20%281%29.pdf
https://hal.univ-antilles.fr/hal-01203244/file/Plos%20Cladonema.pdf