Sulfide-oxidizing bacteria in the burrowing echinoid,Echinocardium cordatum (Echinodermata) |
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Authors: | A Temara C de Ridder J G Kuenen L A Robertson |
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Institution: | (1) Laboratoire de Biologie marine, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, C.P. 160, B-1050 Bruxelles, Belgium;(2) Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, P.O. Box 5057, 2600 GB Delft, The Netherlands |
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Abstract: | Symbiotic filamentous bacteria thrive in the intestinal caecum of the deposit-feeding echinoid Echinocardium cordatum. Specimens of E. cordatum were collected at Wimereux (Nord Pas-de-Calais, France) in 1991. Their symbiotic bacteria build nodules by forming multilayered mats around detrital particles that enter the caecum. The morphological features of the bacteria are those of Thiothrix, a sulfide-oxidizing genus. The filaments, which may form rosettes, are sheathed and made by a succession of hundreds of rod-shaped bacteria which store elemental sulfur in the presence of external sulfide. Live bacteria are restricted to the outer layers of the nodules. Their sulfide-oxidizing activity was investigated, using a Biological Oxygen Monitor, by measuring the O2-consumption when reduced sulfur compounds are provided. They oxidize thiosulfate and sulfide. Optimal sulfide oxidation occurs at intermediary pO2 (100 to 160 M O2l-1). Spectrophotometry has confirmed that the sulfur content of the filamentous symbiotic sulfideoxidizing bacteria depends on the presence of external sulfide. This is the first report of symbiotic intradigestive Thiothrixspp.-like bacteria; it lengthens the list of symbioses between sulfide-oxidizing bacteria and invertebrates from sulfide-rich habitats. |
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