Glycogen storage in the Riftia pachyptila trophosome: contribution of host and symbionts

ABSTRACT: Glycogen storage in host tissue and symbiotic bacteria in the anterior trophosome of thevestimentiferan tubeworm Riftia pachyptila Jones, 1981, was investigated using transmission elec-tron microscope and stereological methods. The relative glycogen content (RGC) of each partner wascalculated from the percentage of host and bacterial cytoplasm area taken up by glycogen and fromthe percentage area that host and symbionts occupy within a trophosome lobule section. Our resultsshow that host and symbionts contribute equally to the total glycogen content of the trophosome; thisratio remains similar for up to 40 h of hypoxia. Furthermore, there is a glycogen gradient in thelobule. In both symbiotic partners, the glycogen content increased from the lobule center towardthe periphery, implying different metabolic activities of host cells and bacteria depending on theirlocation within a trophosome lobule.KEY WORDS: Glycogen · Riftia pachyptila · Symbiosis · Trophosome · Chemoautotrophic bacteria ·Hydrothermal vents