@MrMoody - I don’t think that you need to genetically engineer it to get that result. Biosynthesis is one of the ways they use it, and I think it could be adapted to treating the soil the way that you’ve described.
Usually there are less exotic ways of amending the soil, which is what you’re describing, than engineering the bacteria. Typically people just dump a bunch of fertilizer down. That’s what I did, anyway, and my grass grew like weeds (so did the weeds, for that matter).
But perhaps you could mix the bacteria into the fertilizer in soil samples that are particularly resistant to standard treatments and get a better response.