Microbe

Microbe, microscopic organism (microorganism). The term commonly includes bacteria, archaea, protozoa, algae, fungi, viruses, and microscopic parasites. The study of microbes is called microbiology. Microbes that live in extreme environments or habitats characterized by high or low temperatures or pressures, raised acidity or alkalinity, absence of sunlight or oxygen, or other hostile physical or chemical conditions are called extremophiles. The possible existence of microbes on other planets or bodies in space is an area of study in astrobiology.