Microbes can be engineered to produce almost anything a plant or an animal makes: proteins, flavours, fuels, materials.

Getting microbes to work in a laboratory flask is usually the easy part.

The harder step is making them behave the same way in a tank that holds tens of thousands of litres.

The reason is that scale changes the physics.

Oxygen reaches cells differently, mixing is uneven, heat builds where it did not before, and the organism responds to all of it.