FANG, JIASONG, P. A. COMET, J. M. BROOKS, and R. SASSEN, Geochemical and Environmental Resource Group, Texas A&M Univ., College Station, TX

ABSTRACT: Thiotropic Symbiosis of Seep Vestimentiferan: A Molecular Isotope Perspective

The delta{13}C of individual fatty acids (C<16> - C<22>) isolated from vestimentiferan (Escarpis sp.) from the Gulf of Mexico hydrocarbon seeps have been determined by gas chromatography-isotope ratio mass spectrometry.

Fatty acids of the vestimentiferan have very negative delta{13}C, from -31.6 to -33.3 o/oo, which are significantly lighter than the delta{13}C oftrophosome and vestimentum of the vestimentiferan tissue (-35.5 o/oo and -36.2 o/oo, respectively). The results suggest that the host initially incorporates inorganic carbon in four-carbon compounds such as malate and succinate, which are ultimately decarboxylated. The symbiotic bacteria then take up CO2 respired by the host animal, and the CO2 is subsequently refixed by the symbiotic bacteria through the Calvin cycle in a manner analagous to C<4> plants. High chemoautotrophic capacity stimulates a corresponding high carbon demand and consequently create an efficient fixation of CO2 by the symbiotic bacteria. The accelerated fixation o CO2 causes the residual DIC pool in the vestimentiferan body (the internal CO2 pool) to become enriched in {13}C. Therefore the metabolites of the bacteria (fatty acids) would have heavier delta{13}C values as observed compared to the animal tissues.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.