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 Wiley-Blackwell
Résumé : International audience
In this multidisciplinary study, we combined morphological, physiological, and phylogenetic approaches to identify three dominant water bloom-forming Cyanobacteria in a tropical marine mangrove in Guadeloupe (French West Indies). Phylogenetic analysis based on 16S rRNA gene sequences place these marine Cyanobacteria in the genera Oscillatoria (Oscillatoria sp. clone gwada, strain OG) or Planktothricoides (Candidatus Planktothricoides niger' strain OB and Candidatus Planktothricoides rosea' strain OP; both provisionally novel species within the genus Planktothricoides). Bioassays showed that Candidatus Planktothricoides niger' and Candidatus Planktothricoides rosea' are toxin-producing organisms. This is the first report of the characterization of Cyanobacteria colonizing periphyton mats of a tropical marine mangrove. We describe two novel benthic marine species and provide new insight into Oscillatoriaceae and their potential role in marine sulfide-rich environments such as mangroves.
ISSN: 0378-1097

hal-01536679
https://hal.archives-ouvertes.fr/hal-01536679
DOI : 10.1111/1574-6968.12551

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Beggiatoaceae, giant sulphur-oxidizing bacteria, are well known to occur in cold and temperatewaters, as well as hydrothermal vents, where they form dense mats on the floor.However, they have never been described in tropical marine mangroves. Here, we describetwo new species of benthic Beggiatoaceae colonizing a marine mangrove adjacent to mangroveroots. We combined phylogenetic and lipid analysis with electron microscopy in orderto describe these organisms. Furthermore, oxygen and sulphide measurements in and exsitu were performed in a mesocosm to characterize their environment. Based on this, two new species, Candidatus Maribeggiatoa sp. and Candidatus Isobeggiatoa sp. inhabiting tropical marine mangroves in Guadeloupe were identified. The species identified as CandidatusMaribeggiatoa group suggests that this genus could harbour a third cluster with organisms ranging from 60 to 120 μm in diameter. This is also the first description of an Isobeggiatoa species outside of Arctic and temperate waters. The multiphasic approach also gives information about the environment and indications for the metabolism of these bacteria. Our study shows the widespread occurrence of members of Beggiatoaceae family and provides new insight in their potential role in shallow-water marine sulphide-rich environments such as mangroves.
ISSN: 1932-6203

hal-01205641
https://hal.univ-antilles.fr/hal-01205641
https://hal.univ-antilles.fr/hal-01205641/document
https://hal.univ-antilles.fr/hal-01205641/file/Beggiatoa%20Plosone2015.pdf
DOI : 10.1371/journal.pone.0117832

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