Presumably it would be from ammonia, fixed artificially, just as it often is with crops grown the ordinary way. It would probably convert the nitrogen to protein more efficiently.

The interesting question is the energy source.

> solarfoods.com

It is in the name

I meant the proximate energy source. Are the organisms photosynthetic? Or is solar energy converted to something else? For example, is PV used to make electricity that then powers the microorganisms (by providing them with reduced metal ions they can oxidize)? Or is a chemical energy source synthesized, say methanol as was used for ICI's Pruteen (although that process sourced the methanol from natural gas)?