E. coli is useful as it grows very quickly so you don’t have to wait around for it to make lots of your protein. It has a doubling time of 20 minutes at 37’C. It’s also very robust so you can’t kill it by accident (although you can with disinfectant). The E. coli we use is a special strain which cannot survive without specific nutrients which we give it in the lab. It’s not quite the same as the one you hear about in the news with food poisoning. It means it cannot contaminate the local area.