Some microorganisms are useful and some are harmful to us. Yeast is an example of microorganism that is widely used in the food industry. Yeast is a fungus. It it used in the making of bread, cheese, tempeh and tapai. When yeast is added to a sugar solution, it use the sugar as a source of food. When it breathes it takes in oxygen and releases carbon dioxide. Carbon dioxide makes the bread dough rise. In tempeh, the white thread that can be seen is the mycelium of the fungus when it grows. If kept too long, the fungus will then produce black reproductive structures called spores.
Some bacteria, such as Lactobacillus is widely used in making yogurt drink. Antibiotics such as penicillin is extracted from Penicillium,which is a fungus. Bacteria nad fungi in soil will act on grass and leaves or any other organic materials and convert them to humus by a process known as biodegradation.