Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 9 2010 10.5194/bg-7-2591-2010 http://www.biogeosciences.net/7/2591/2010/ http://www.biogeosciences.net/7/2591/2010/bg-7-2591-2010.html http://www.biogeosciences.net/7/2591/2010/bg-7-2591-2010.pdf 2591 2600 2010-09-02 Tracing carbon assimilation in endosymbiotic deep-sea hydrothermal vent Mytilid fatty acids by ¹³C-fingerprinting V. Riou virginie_riou@hotmail.com S. Bouillon R. Serrão Santos F. Dehairs A. Colaço Department of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium Department of Oceanography and Fisheries, IMAR-University of Azores, Horta, Portugal Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Leuven, Belgium <i>Bathymodiolus azoricus</i> mussels thrive at Mid-Atlantic Ridge hydrothermal vents, where part of their energy requirements are met via an endosymbiotic association with chemolithotrophic and methanotrophic bacteria. In an effort to describe phenotypic characteristics of the two bacterial endosymbionts and to assess their ability to assimilate CO₂, CH₄ and multi-carbon compounds, we performed experiments in aquaria using ¹³C-labeled NaHCO₃ (in the presence of H₂S), CH₄ or amino-acids and traced the incorporation of ¹³C into total and phospholipid fatty acids (tFA and PLFA, respectively). 14:0; 15:0; 16:0; 16:1(<i>n</i> − 7)<i>c+t</i>; 18:1(<i>n</i> − 13)<i>c+t</i> and (<i>n</i> − 7)<i>c+t</i>; 20:1(<i>n</i> − 7); 20:2(<i>n</i> − 9,15); 18:3(<i>n</i> − 7) and (<i>n</i> − 5,10,13) PLFA were labeled in the presence of H¹³CO₃⁻ (+H₂S) and ¹³CH₄, while the 12:0 compound became labeled only in the presence of H¹³CO₃⁻ (+H₂S). In contrast, the 17:0; 18:0; 16:1(<i>n</i> − 9); 16:1(<i>n</i> − 8) and (<i>n</i> − 6); 18:1(<i>n</i> − 8); and 18:2(<i>n</i> − 7) PLFA were only labeled in the presence of ¹³CH₄. 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