Having evolved from the very widespread Photosagnia, the Nitromoeba began to respire nitrogen in the environment from the long time it spent along the seafloor consuming detritus. The logical next step for this organism was to begin to metabolize the most common substance from decay, and so kickstarted the nitrogen cycle on Sagan 4.
Once a creature excretes waste or there is decomposing matter, the consuming cells will begin to strip it away, thus releasing ammonia compounds. Nitromoeba cells will then begin to fix this ammonia for release back into the environment as nitrogen by converting it into energy for itself, the result is a much more habitable biosphere.
Along the coastline, crystal flora also play a role by using these newly synthesized nitrites for their own metabolization. The cycle is not yet fully realized, but given some time there should be more metabolizers to the point where they need only use nitrogen for energy and nothing else.