Io is the only human to show up in Prometheus Bound, but conflict between man and the natural world is central to the play: basically, Prometheus gets on Zeus's bad side by helping humans to become more than beasts. The most important piece of knowledge Prometheus can impart to humans is the secret of fire—previously known only to the gods. Fire, in this play, doesn't merely make it possible to control the natural world; it will eventually help humans discover Facebook and Instagram. Hm, double-edged sword, indeed.
After Prometheus shares his knowledge with humans, they acquire power over nature similar to what the gods enjoy.
The play portrays nature as basically hostile to humans, but it also shows that humans can use technology to make nature more hospitable for them.