Bigelowii itself seems very interesting, even without this nitrogen fixing organelle, having two completely different phases to it's life - one in a weird dodecahedral calcareous shell and one without as a mobile flagellate. Apparently it can exist and reproduce in either form, and occasionally switch forms. It took scientists a long while to realize the two forms are actually the same species.
The "tokoroten" noodles are just agar.
Pretty much everyone in biology tries growing cells in agar, right? Surely that can't have been an amazing discovery?
https://en.wikipedia.org/wiki/Plastid
Edit: "It was a type of algae called Braarudosphaera bigelowii. Hagino fondly just calls it Bigelowii."
Is this pronounced bigggie-lowie?
In contrast, excessive bio-available nitrogen is unlikely to build up when there a huge capability and not-really-metaphorical appetite for consuming it and turning it back into N2 gas.