When you flush the toilet or drain your tub, the water goes into the sewer. It's not a place your mom would want you looking for stuff. This special bacteria releases hydrogen gas that could be collected and harnessed as biofuel. A biofuel is something from nature that makes energy. One example is corn that can be processed to make ethanol.
Cars can run on ethanol like they do on gasoline.
And someday cars might even run on bacterial gas. Most people think bacteria are bad news. It's true that many can make you sick. But other bacteria in your stomach protect you from illness. Others help you digest food.