Archaea, bacteria, Protista, fungi, viruses and microbial mergers are divisions that contain microorganisms. Most microorganisms are single-celled organisms. Baker's yeast and fission yeast are unicellular microorganisms.
Archaea are single-celled organisms without a nucleus. Archaea are found in all types of habitats.
Bacteria are complex, single-celled organisms that can survive in extreme environments. Bacteria are responsible for making vitamins, breaking down material and maintaining the atmosphere. Bacteria appeared on Earth billions of years ago.
Microbe World explains that many species of fungi are classified as microorganisms. Fungi that are microorganisms share one cellular wall with multiple nuclei scattered throughout the organism.
Protista are eukaryotic microorganisms that have their DNA enclosed in a nucleus. Single-celled algae, protozoa, slime molds and water molds are the four subgroups of the Protists.
Viruses are microorganisms that do not fit into the living or non-living groups. In their inert states, viruses act as non-living creatures, but once they are exposed to a suitable host, they exhibit lifelike qualities. Viruses are simple microorganisms that are 10,000 times smaller than bacteria. Viruses contain small amounts of genetic material.
Microbial mergers are microorganisms that include Rhizobia, Mycorrhizae and Zooxanthelle. Each of these microorganisms shares a mutual relationship with another organism.