that does not mean there is no byproduct. Bacteria can produce more bacteria by degrading manure into compost. Yet they also release methane in the process.
Other example closer to the subject a recent study about a modified version of the infamous e.coli bacteria that could degrade plastics. One of the outproduct is paracetamol. Which is cool in a lab, not so much in your body our in river waters.
https://www.nature.com/articles/d41586-025-01986-0