Nitrogen fixation in termites: Fate of newly fixed nitrogen

Nitrogen (¹⁵N) fixed by gut symbionts of the termite Nasutitermes corniger is assimilated and incorporated into termite tissues. Metabolic differences between soldier and worker castes are reflected in assimilation patterns: a greater proportion of the newly fixed nitrogen was in the bodies of workers but in the heads of soldiers. Newly fixed nitrogen is also transferred between workers and soldiers by trophallaxis. These studies confirm the 3:1 ratio assumed as the affinity of nitrogenase for acetylene relative to nitrogen in the acetylene-reduction method.