What is the role of living tiny organisms in human life?

Single-celled organisms play a very important role both in natural processes and in human economic activity. Since ancient times, yeast and various bacteria have helped to obtain such drinks as kvass, beer, wine, kefir, yogurt, and bake bread. By recycling organic waste, bacteria cleanse the environment and participate in the formation of fertile soil. Bacteria living in the stomach and intestines of humans and domestic animals are important, digesting solid plant foods.