INTRACELLULAR COEXISTENCE OF METHANOTROPHIC AND THIOAUTOTROPHIC BACTERIA IN A HYDROTHERMAL VENT MUSSEL

The coexistence of two phylogenetically distinct symbiont species with in a single cell, a condition not previously known in any metazoan, is demonstrated in the gills of a Mid-Atlantic Ridge hydrothermal vent m ussel (family Mytilidae). Large and small symbiont morphotypes within the gill bacteriocytes are shown to be separate bacterial species by m olecular phylogenetic analysis and fluorescent in situ hybridization, The two symbiont species are affiliated with thioautotrophic and metha notrophic symbionts previously found in monospecific associations with closely related mytilids from deep-sea hydrothermal vents and hydroca rbon seeps.