Physiological and immunological evidence for two distinct C1-utilizing pathways in Bathymodiolus puteoserpentis (Bivalvia: Mytilidae), a dual endosymbiotic mussel from the Mid-Atlantic Ridge |
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Authors: | J J Robinson M F Polz A Fiala-Medioni C M Cavanaugh |
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Institution: | (1) Department of Organismic and Evolutionary Biology, Harvard University, Biological Laboratories, 16 Divinity Ave., Cambridge, Massachusetts 02138, USA, US;(2) Observatoire Oceanologique (Laboratoire Arago), F-66650, Banyuls-sur-Mer, France, FR |
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Abstract: | The existence of endosymbiotic sulfur-oxidizing chemoautotrophic and methanotrophic bacteria associating with marine mytilid
mussels has previously been inferred by 16S rDNA analysis in Bathymodiolus puteoserpentis Von Cosel et al. 1994, a hydrothermal vent mussel from a site on the Mid-Atlantic Ridge. In mussels collected in June 1993,
we found evidence of enzymes diagnostic of two distinct C1 assimilation pathways in this symbiosis. Assays for the utilization of radiolabelled methane and for immunodetection of methanol
dehydrogenase were positive, indicating that oxidation and incorporation of this substrate are occurring in this symbiosis.
Sulfide or thiosulfate had no detectable stimulatory effect on CO2 incorporation, and assays for the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), an enzyme diagnostic
for the Calvin–Benson cycle, were negative. RubisCO was detected in all samples examined by immunoblot analysis, indicating
this enzyme is expressed in the B. puteoserpentis symbiosis. Stable isotope data showed that carbon isotope values were in agreement with previously reported values, and nitrogen
isotope values were among the most depleted ever reported for bivalve symbioses. The carbon isotope values do not preclude
the utilization of vent-derived methane. These data could be explained by the presence of two metabolically distinct bacterial
symbionts or a Type X methanotrophic symbiont.
Received: 3 October 1997 / Accepted: 23 July 1998 |
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