CARBON RELEASE FROM PURIFIED CHEMOAUTOTROPHIC BACTERIAL SYMBIONTS OF THE HYDROTHERMAL VENT TUBEWORM RIFTIA-PACHYPTILA

The gutless hydrothermal tubeworm Riftia pachyptila Tones relies mainl y on its chemoautotrophic bacterial symbionts to supply nutrients in t he form of secreted organic compounds resulting from fixation and inco rporation of CO2. In this study, symbionts were purified, tested for v iability, and incubated in the presence of labeled CO2. We demonstrate d that purified symbionts can be used as a viable alternative to exper iments with bacterial cultures. Several organic acids, sugars, and ami no acids were labeled, but their fraction of the total label stayed ge nerally constant during the incubation times used. However, increasing fractions of succinate and, to a lesser degree, glutamate were excret ed into the incubation medium, indicating that these are probably the main carbon-containing compounds transferred from the symbionts to the host. Glutamate could also account for the transport of nitrogen from the symbionts to the host.