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Applied and Environmental Microbiology, May 2009, p. 3304-3313, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02659-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Effects of Long-Term Starvation on a Host Bivalve (Codakia orbicularis, Lucinidae) and Its Symbiont Population{triangledown}

Audrey Caro,1,2* Patrice Got,1 Marc Bouvy,1,3 Marc Troussellier,1 and Olivier Gros2

UMR-CNRS 5119, Laboratoire Ecosystèmes Lagunaires, Case 93, Université Montpellier II, 34095 Montpellier Cedex 5, France,1 UMR-CNRS 7138, Systématique-Adaptation-Evolution, Equipe Symbiose, Université des Antilles et de la Guyane, UFR des Sciences Exactes et Naturelles, Département de Biologie, B.P. 592, 97159 Pointe-à-Pitre Cedex, Guadeloupe, France,2 IRD, UMR 5119, Laboratoire Ecosystèmes Lagunaires, Université Montpellier II, Case 093, 34095 Montpellier Cedex 5, France3

Received 20 November 2008/ Accepted 16 March 2009

The bivalve Codakia orbicularis, hosting sulfur-oxidizing gill endosymbionts, was starved (in artificial seawater filtered through a 0.22-µm-pore-size membrane) for a long-term experiment (4 months). The effects of starvation were observed using transmission electron microscopy, fluorescence in situ hybridization and catalyzed reporter deposition (CARD-FISH), and flow cytometry to monitor the anatomical and physiological modifications in the gill organization of the host and in the symbiotic population housed in bacteriocytes. The abundance of the symbiotic population decreased through starvation, with a loss of one-third of the bacterial population each month, as shown by CARD-FISH. At the same time, flow cytometry revealed significant changes in the physiology of symbiotic cells, with a decrease in cell size and modifications to the nucleic acid content, while most of the symbionts maintained a high respiratory activity (measured using the 5-cyano-2,3-ditolyl tetrazolium chloride method). Progressively, the number of symbiont subpopulations was reduced, and the subsequent multigenomic state, characteristic of this symbiont in freshly collected clams, turned into one and five equivalent genome copies for the two remaining subpopulations after 3 months. Concomitant structural modifications appeared in the gill organization. Lysosymes became visible in the bacteriocytes, while large symbionts disappeared, and bacteriocytes were gradually replaced by granule cells throughout the entire lateral zone. Those data suggested that host survival under these starvation conditions was linked to symbiont digestion as the main nutritional source.

* Corresponding author. Mailing address: UMR-CNRS 5119, Laboratoire Ecosystèmes Lagunaires, Case 93, Université Montpellier II, 34095 Montpellier Cedex 5, France. Phone: 33 (0)4 67 14 41 85. Fax: 33 (0)4 67 14 37 19. E-mail: audrey.caro{at}univ-montp2.fr

{triangledown} Published ahead of print on 3 April 2009.

Applied and Environmental Microbiology, May 2009, p. 3304-3313, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02659-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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