A microscopic living organism that is too small to be seen with the naked eye. Microorganisms are simple life forms and usually unicellular. Commonly used microorganisms in industrial processes include bacteria, fungi, and protozoa, and are noted for their rapid rate of reproduction and ability to utilize waste products as substrates such as agricultural waste. They can be cultivated in batch and continuous processes, and on a large scale with high yields. Certain microorganisms can be genetically manipulated through recombinant DNA technology and other techniques to produce bioproducts such as viral antigens without the need for alternative hazardous processes. They usually produce non-toxic waste products.