What is a microorganism?: A microorganism or microbe is a single-celled or multi-celled microscopic organism. The study of microorganisms is called microbiology. Anton van Leeuwenhoek is considered the pioneer of microscopy – he discovered microorganisms in the year 1675, using a microscope he designed.
What are the types of microorganisms?: Microorganisms include all prokaryotes namely the bacteria and archaea and few eukaryotes, comprising the protozoa, fungi, algae and animals like rotifers and planarians. Viruses are sometimes classified as microbes but it is difficult to classify them under living organisms because they reproduce only when they are within a host. Outside the host they crystallize and resemble a non-living object. Most microorganisms are microscopic, but there are some like Thiomargarita namibiensis which are macroscopic and can be seen with the naked eye.
Where do microorganisms live?: Microorganisms live in every part of the biosphere including soil, hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth's crust. Microorganisms play an important role in nutrient cycling and decomposition in the ecosystem. Some bacteria can fix nitrogen and help in plant growth.