If we were to lose all the CO2 in the atmosphere, we will all very quickly die. Plants require it to survive. [1]

The problem with bacteria, is that thanks to exponential growth, and an inability to control them, we can end up in deep, deep trouble. Using them in a controlled fashion that will bring us from 400ppm to 250ppm (but no lower) seems incredibly unlikely. Either they won't be able to make a big difference, or they'll bring us to a level far below habitable.

[1] https://en.wikipedia.org/wiki/Future_of_Earth

Agreed, but in this case no cadmium semiconductors == no super bacteria. They can't build semiconductors, we do, so we control the reaction. Are we really going to use up all CO2, stop photosynthesis and suffocate? I don't believe so. We also keep producing plenty of CO2.