First Description of Sulphur-Oxidizing Bacterial Symbiosis in a Cnidarian (Medusozoa) Living in Sulphidic Shallow-Water Environments

Abstract

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.

Thioautotrophic ectosymbiosis in Pseudovorticella sp., a peritrich ciliate species colonizing wood falls in marine mangrove

“…Samples for SEM were fixed in 0.22 m-filtered 4% paraformaldehyde solution in seawater at 4 • C. They were then dehydrated in graded concentrations of acetone, critical point dried in CO 2 and sputter-coated with gold before observation with a FEI Quanta 250 running at 20 kV (Abouna et al 2015;Jean et al 2015).…”

“…After a brief rinse in the same buffer, they were fixed for 45 min at room temperature in 1% osmium tetroxide in the same buffer, rinsed in distilled water and post-fixed with 2% aqueous uranyl acetate for 1 h at room temperature. Samples were dehydrated in graded concentration of acetone before embedding in epoxy resin and observation in a FEI Tecnai F20 running at 200 kV (Abouna et al 2015;Gros et al 2012).…”

“…Sequences were aligned using MUSCLE and alignments were checked manually. Regions of ambiguous or uncertain alignment were eliminated from consideration (Abouna et al 2015). Phylogenetic analyses were performed using the programs MEGA version 7 (Kumar et al 2016).…”

“…In Guadeloupe's mangrove, endosymbiotic sulfur-oxidizing bacteria were previously described inside the gills of Phacoides pectinatus living in the sediment (Frenkiel et al 1996). On the other hand, ectosymbiosis occurs between sulfur-oxidizing bacteria and ciliates (Laurent et al 2009;Maurin et al 2010), nematoda (Himmel et al 2009;Maurin et al 2010) and polypes of medusozoa (Abouna et al 2015). To our knowledge, the only thiotrophic relationship involving ciliates described from mangrove wood falls ecosystem concerns the peritrich ciliate Zoothamnium niveum and sulfur oxidizing bacteria (Bauer-Nebelsick et al 1996b;Laurent et al 2009;Maurin et al 2010;Ott et al 2004).…”

Impacts ofDesulfobacteralesandChromatialeson sulfate reduction in the subtropical mangrove ecosystem as revealed by SMDB analysis

“…Mangrove sediments have similar pH, temperature, and salinity as tropical marine environments (Abouna et al, 2015). To analyze the effects of mangrove ecosystems on dissimilatory sulfate reduction, we assumed that these ecosystems receive identical sulfur contents at the same place.…”