Microbiology is the study of organisms too small to be seen with the naked eye. Originally, emphasis was placed on harmful microorganisms which cause disease or spoilage of beverages and food, but it is now recognized that many microbes have essential roles in our ecosystem or can be used to accomplish beneficial tasks.
Human history is full of examples of major devastations caused by bacteria and viruses.
Some of these historically important diseases still occur, such tuberculosis and yellow fever. Microorganisms are evolving to cause new infectious disease problems such as Lyme disease and AIDS, which capture public attention. Control and eradication of infectious diseases remain important goals of many microbiologists. Microorganisms in soil and water are essential in the transformation of carbon, nitrogen, oxygen, sulfur and iron to products needed by plants and animals. In various ways, microbes participate in environmental cycling and degradation and global change.