[flobosg]

I’m not sure if I’m following you correctly. If a non-reactive strain is evolved, by definition it will be unable to establish itself in the plant nodules, and that niche will still be occupied by reactive, symbiosis-capable bacteria. Besides, the signal for ammonia production, rhizopine, is actually a sugar-like compound.

[foerbert]

I don't think you can just "by definition" reality like that. Sure, the non-reactive strain won't be called a symbiotic partner, by definition. But that doesn't poof the bacteria out of existence.

That said, I think you're correct about not being so concerned. If the symbiotic relationship was so exploitable, it'd probably be a great evolutionary advantage to do so. The signal being a sugar itself, as you note, doesn't surprise me.

[flobosg]

> But that doesn't poof the bacteria out of existence.

By “definition” I meant “the rhizopine signaling pathway”, implying that no pathway → no symbiosis. Of course that signal insensitive strains or species can exist. It’s a symbiote and not a parasite, after all.