Microbes in ecosystems: Every organism serves a function. Most microbes do not cause disease. Some microbes are beneficial to humans. Bacteria is used in making cheese, yogurt and making leather. Microbes in our body help us digest food in our stomach, fight infections with our immune system and stay healthy. Microbes in ecosystems are useful. They break down complex molecules in food and return nutrients to the soil so other organisms can grow. Imagine apples piling up under a tree being unable to decompose (rot) without microbes to "break them down" [Nutrient Cycling]. Four Types of Microbes: Viruses, Bacteria (some), Protozoans & Fungus. Four of microbes: HIV, gangrene, malaria & molds.