Astrophage biology question

I’m confused as to how astrophage breeding works. Full book spoilers ahead. >!We’re told that they have pretty much earth biology building blocks (DNA is specifically mentioned). So how the hell can they reproduce in 100% CO2 atmosphere? Let’s say they get hydrogen from the sun and make water from hydrogen and CO2. Where are they getting P and N to make more DNA? It has to double for any cell to reproduce and that’s probably at least a million base pairs to be made out of nothing. (I’m not even talking about the whole show them the spectral lines to multiply. I’m assuming they just took CO2 out of Earth’s atmosphere).!<

I did a brief look through and didn’t see this question asked. Feel free to point me to a thread where this was already discussed.