Imagine giant tanks of bacteria producing whatever chemicals we need

Harvard professors are working on it. The idea of tanks of microbes making things isn't new - remember the giant tanks of Chinese hamster ovary cells along the Charles in Allston - but the Harvard boffins say they've figured out how to up the production of whatever 30fold:

The technique makes a desired chemical product essential to the bacteria’s survival by modifying their DNA so that antibiotic-resistant genes are activated, but only in the presence of a certain chemical, such as the one that is desired for production. At the same time, the genetic modification makes the low-output chemical producers highly susceptible to being killed off by antibiotics. Only the most productive cells generate enough of the desired chemical to be completely resistant to the antibiotic and survive to the next round of evolution. As each evolution cycle progresses, the bacteria become more and more effective at producing the desired chemical as they use the “survival of the fittest” principle to stamp out the weakest producer cells.