THE COOCCURRENCE OF METHANOTROPHIC AND CHEMOAUTOTROPHIC SULFUR-OXIDIZING BACTERIAL SYMBIONTS IN A DEEP-SEA MUSSEL

In April 1990 a new species of mytilid containing bacterial endosymbio nts was discovered at a deep-water seep site within Alaminos Canyon in the Gulf of Mexico. Activities of ribulose bisphosphate carboxylase/o xygenase and ATP sulfurylase, as well as the presence of substantial l evels of elemental sulfur in the gill tissues indicate the presence of chemoautotrophic sulfuroxidizing symbionts in the gills. Methanol deh ydrogenase activity and the tissue stable carbon isotope ratios indica te the presence of methanotrophic bacteria in the gills of the same an imals. Two distinct size classes and morphological types of gram negat ive bacteria are visible in transmission electron micrographs of the g ill tissue, one of which contains the complex internal membranes typic al of methanotrophs. Both general types of symbionts have been demonst rated singly in related species of deep-sea mytilids. In this species, however, both types are found in single individuals, often within the same cell vacuole.