There are 6 major recognized microbial groups:
The oldest living organisms, bacteria can be found in every part of the planet. These single-celled microbes feed on both organic and non-organic matter. Some bacteria also have ability to make their own food from light or chemical energy using carbon dioxide. Bacteria play a vital role in the environment.
Archaea is a single-celled microbe which until 1970 was classified under bacteria. They are similar in some ways to bacteria, but distinct enough to get their own classification. Unlike bacteria, some of the archaea could be found in extreme environment conditions, such as extreme temperatures or water salinity.
Single-celled organisms which are found both in water and on the land, but mostly in moist environment. Protozoa gets its food from organic matter – either feeding on living organisms or organic debris.
These water-loving micro-organism of (usually) green color could take the form of single celled, multi-celled and some even-celled chains. All of these microbes have a pigment called Chlorophyll A, which actually gives most algae its green color. Some algae has also other pigments present, hence not all of algae are green. These microbes are capable of generating their own food through photosynthesis (just like plants).
Fungi are single-celled or multicellular microbes which mostly can be found on the ground rather than in aquatic environment. Fungi are decomposers, which means they make things rot. Some fungi feed on dead organisms, but some also on living ones.
The last and the most important in this course group of microorganisms is viruses. They are the smallest of all the microbes and need a living cell to exist. Viruses can infect any living cell – people, humans, plants and even bacteria! Viruses exist to create more viruses. Once they replicate in a host cell, they can leave to infect another living cell.