Tracing carbon assimilation in endosymbiotic deep-sea hydrothermal vent Mytilid fatty acids by sup13/supC-fingerprinting

摘要

Bathymodiolus azoricus mussels thrive at Mid-Atlantic Ridge hydrothermal vents, where part oftheir energy requirements are met via an endosymbiotic association withchemolithotrophic and methanotrophic bacteria. In an effort to describephenotypic characteristics of the two bacterial endosymbionts and to assesstheir ability to assimilate CO₂, CH₄ and multi-carbon compounds,we performed experiments in aquaria using 13C-labeled NaHCO₃ (inthe presence of H₂S), CH₄ or amino-acids and traced theincorporation of 13C into total and phospholipid fatty acids (tFA andPLFA, respectively). 14:0; 15:0; 16:0; 16:1(n ? 7)c+t; 18:1(n ? 13)c+t and (n ? 7)c+t;20:1(n ? 7); 20:2(n ? 9,15); 18:3(n ? 7) and (n ? 5,10,13) PLFA were labeled in thepresence of H13CO₃? (+H₂S) and 13CH₄, whilethe 12:0 compound became labeled only in the presence ofH13CO₃? (+H₂S). In contrast, the 17:0; 18:0; 16:1(n ? 9);16:1(n ? 8) and (n ? 6); 18:1(n ? 8); and 18:2(n ? 7) PLFA were only labeled in thepresence of 13CH₄. Some of these symbiont-specific fatty acidsalso appeared to be labeled in mussel gill tFA when incubated with13C-enriched amino acids, and so were mussel-specific fatty acids suchas 22:2(n ? 7,15). Our results provide experimental evidence for the potentialof specific fatty acid markers to distinguish between the two endosymbioticbacteria, shedding new light on C₁ and multi-carbon compound metabolicpathways in B. azoricus and its symbionts.