Major group of microorganisms are as follows
Bacteria are small single-celled organisms. Their cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. Hence they are also called as prokaryotic organisms. Bacteria are classified into five groups according to their basic shapes: spherical shaped, rod shaped, spiral shaped, comma shaped and corkscrew shaped. They can exist as single cells, in pairs, chains or as clusters. They are found in every habitat like in soil, rock, oceans and even arctic snow. Some species can live under extreme conditions of temperature and pressure. Some live as host in other organisms including plants, animals and humans. They play an important role in the cycling of nutrients. Some species cause food spoilage and crop damage while others are incredibly useful in the production of fermented foods.
Fungi are eukaryotic organisms as their cells contain membrane-bound organelles and well defined nuclei. Fungi are the species of organisms, which includes the yeasts, rusts, smuts, mildews, molds, and mushrooms. They are of great environmental and medical importance. Many fungi are free-living in soil or water while others form parasitic or symbiotic relationships with plants or animals.
A group of single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and plant debris. It consists of the single-celled microscopic organisms which include amoebas, flagellates, ciliates, sporozoans, and many other forms. They live in a wide variety of moist habitats including fresh water, marine environments and the soil.
Algae are a diverse group of aquatic organisms that have the ability to conduct photosynthesis. They play ecological roles as oxygen producers and as the food base for almost all aquatic life. They are economically important as a source of crude oil and as sources of food and a number of pharmaceutical and industrial products for humans. The study of algae is called phycology,
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria. They invade living normal cells and use those cells to multiply and produce other viruses like themselves. They are found in almost every ecosystem on earth and are the most numerous type of biological entity. The study of viruses is known as virology.