title: Comparative modifications in bacterial gill-endosymbiotic populations of the two bivalves Codakia orbiculata and Lucina pensylvanica during bacterial loss and reacquisition.
abstract: Until now, the culture of sulphur-oxidizing bacterial symbionts associated with marine invertebrates remains impossible. Therefore, few studies focused on symbiont's physiology under stress conditions. In this study, we carried out a comparative experiment based on two different species of lucinid bivalves (Codakia orbiculata and Lucina pensylvanica) under comparable stress factors. The bivalves were starved for 6 months in sulphide-free filtered seawater. For C. orbiculata only, starved individuals were then put back to the field, in natural sediment. We used in situ hybridization, flow cytometry and X-ray fluorescence to characterize the symbiont population hosted in the gills of both species. In L. pensylvanica, no decrease in symbiont abundance was observed throughout the starvation experiment, whereas elemental sulphur slowly decreased to zero after 3 months of starvation. Conversely, in C. orbiculata, symbiont abundance within bacteriocytes decreased rapidly and sulphur from symbionts disappeared during the first weeks of the experiment. The modifications of the cellular characteristics (SSC--relative cell size and FL1--genomic content) of the symbiotic populations along starvation were not comparable between species. Return to the sediment of starved C. orbiculata individuals led to a rapid (2-4 weeks) recovery of symbiotic cellular characteristics, comparable with unstressed symbionts. These results suggest that endosymbiotic population regulation is host-species-dependent in lucinids.
authors.affiliation: UMR 7138 UPMC-CNRS, Equipe "Biologie de la Mangrove", Département de Biologie, UFR des Sciences Exactes et Naturelles, Université des Antilles et de la Guyane, Pointe-à-Pitre Cedex, Guadeloupe, France.
authors.forename: Nathalie H
authors.initials: NH
authors.lastname: Elisabeth
authors.forename: Audrey
authors.initials: A
authors.lastname: Caro
authors.forename: Thierry
authors.initials: T
authors.lastname: Césaire
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Mansot
authors.forename: Arthur
authors.initials: A
authors.lastname: Escalas
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Sylvestre
authors.forename: Patrick
authors.initials: P
authors.lastname: Jean-Louis
authors.forename: Olivier
authors.initials: O
authors.lastname: Gros
mesh_terms: D000818:Animals; D001419:Bacteria / Q000235:genetics; D018407:Bacterial Physiological Phenomena; D049872:Bivalvia / Q000382:microbiology*; D005880:Gills / Q000737:chemistry / Q000382:microbiology; D013455:Sulfur / Q000032:analysis; D013559:Symbiosis
chemical_list: D013455:Sulfur
keywords: Lucinidae; cell size; endosymbiotic population; genomic content; starvation; sulphur content