Nitrogen fixation (acetylene reduction) associated with the zoanthid Palythoa tuberculosa Esper

Abstract

Nitrogen fixation by the zoanthid Palythoa tuberculosa Esper was determined by the acetylene reduction technique. The samples were collected from Nanwan Bay of Kenting National Park in Taiwan during the period of September 1990 to January 1991. More than 70% of zoanthid samples (10 of 14) showed detectable levels of nitrogenase activity within 16 h of incubation under either aerobic or anaerobic conditions. Most of the zoanthid-associated nitrogen-fixing bacteria were probably distributed on the surface rather than inside the zoanthid tissues. Sixty-one strains in total of marine nitrogen-fixing bacteria belonging to the family Vibrionaceae were isolated from selected zoanthid samples that showed nitrogenase activity. All isolates utilized the combined nitrogen sources of NH 4Cl and yeast extract aerobically and anaerobically, but they fixed N 2 as the sole nitrogen source only under anaerobic conditions. The greatest levels of nitrogenase activity of these isolates were detected at 1–3% NaCl and at 0.5-2% glucose (as a sole source of carbon and energy).