Fatty acid carbon isotope signatures in chemosynthetic mussels and tube worms from gulf of Mexico hydrocarbon seep communities

The δ13C values of specific fatty acids isolated from mussels and two species of tube worm from Gulf of Mexico hydrocarbon seep communities show 13C depletion characteristic of a chemosynthetic food source. The carbon isotopic composition of fatty acids in Lamellibrachia and Escarpia-like tube worms ranged from −29.3‰ to −18.0‰ while the fatty acid C-isotopic composition in the methanotrophic mussel Bathymodiolus childressi ranged from −45.4‰ to−39.6‰ or from −78.8‰ to −68.4‰, depending upon whether thermogenic or biogenic methane was utilized by the methanotrophic symbionts. In most cases, unsaturated fatty acids were depleted relative to saturated fatty acids, indicating de novo transformations.Exceptions some unsaturated 18 carbon fatty acids, which were enriched relative to saturated acids of the same length indicating direct incorporation of the bacterial fatty acids by the host.