Gulf of Mexico hydrocarbon seep communities. 9. Sterol biosynthesis of seep mussels and its implications for host-symbiont association

The sterol analysis of six hydrocarbon seep mussels (mytilid II and mytilid Ib) from the Alaminos Canyon in the Gulf of Mexico is reported. The sterol composition of the mussel-symbiotic bacteria complex reflects a preponderant synthesis of 4 alpha -methyl sterols (seep mytilid II), and a predominant biosynthesis of 4-desmethyl sterols with some amounts of 4 alpha -methyl sterols (seep mytilid Ib). This suggests a methane-based symbiotic relationship between the mussels and methanotrophic bacteria. It also suggests that the biosynthesis of sterols in the mussel-bacteria complex is completed to the level of cholest-5-en-3 beta -ol (mytilid II) or 5 alpha -cholestan-3 beta -ol (mytilid Ib).