For anyone who has wondered, "What is growing in my fridge?" What do permafrost, hydrothermal vents, and hot springs have in common? They all host fungi, of course! The microbes in extreme environments have evolved to deal with some major issues, like being surrounded by poisonous ions that want to drink a cell's water and destroy its proteins.  Izzie goes to the ends of the Earth to find the fungi that are best at living in extremely cold, hot, dry, or salty environments, and some of the microscopic tools that help them survive. Thanks to the Twitter followers who voted on the featured environments.