Bacteria take chemicals out of the environment to run their metabolism. After consuming the right amount of the right chemicals, bacteria have enough chemical energy to reproduce. They do that by splitting themselves in half. Of course, it’s a bit complicated biochemically speaking, but the idea is just that. We call it binary fission—splitting in two. That would be fine for the bacteria, but as they reproduce and metabolize the chemical environment around them, certain of them produce miserable toxins that make us sick.
