Microbes, or microorganisms, are minute living things that individually are usually too small to be seen with the unaided eye. The following are the different types of microorganisms.
- Bacteria are relatively simple, single-celled organisms.
- Archaea, like bacteria, consist of prokaryotic cells.
- Fungi are eukaryotes. Yeasts are the unicellular forms of fungi. Molds are the most typical fungi.
- Protozoa are unicellular eukaryotes.
- Algae are photosynthetic eukaryotes. The algae of interest to microbiologists are usually unicellular.
- Viruses are acellular (i.e., they are not cells). A virus particle contains a core of RNA or DNA surrounded by a protein coat.
- Multicellular animal parasites are not strictly microorganisms but are of medical importance. Animal parasites are eukaryotes.
Microbes that live stably in and on the human body are called the human microbiome, or microbiota.
Bacterial ancestors were the first living cells to appear on Earth.
—September 2020
Lance Jones 