The study of microorganisms, which are unicellular, multicellular or acellular, is microbiology. Microbiology covers numerous sub-disciplines which include virology, bacteriology, protistology, mycology, immunology and parasitology.
Traditionally Microbiologists relied on culture, staining and microscopy. Less than 1% of the microorganisms present in common environments can be cultured in isolation using current means. Microbiologists therefore often rely on molecular biology tools such as DNA sequence-based identification.
Viruses have been variably classified as organisms as they have been considered either very simple microorganisms or very complex molecules. Prions, never considered microorganisms, have been investigated by virologists.
The branches of microbiology can be classified into applied sciences, or divided according to taxonomy, as is the case with bacteriology, mycology, protozoology, virology and phycology. A pure research branch of microbiology is termed cellular microbiology.
Research on microorganisms has suggested that they could be useful in the treatment of cancer. Of course, we all know that there are good microorganisms and bad microorganisms. Most microorganisms do not cause disease and many are beneficial to us.