The major groups of microorganisms are broadly classified into bacteria, fungi, protozoa, algae and viruses, which are highly diversified in nature. The microorganisms show huge diversity among each other, but these can be broadly grouped into the five major groups that we will discuss in this content.

The major groups of microorganisms—namely bacteria, archaea, fungi ( yeasts and molds ), algae, protozoa, and viruses—are summarized below. Links to the more detailed articles on each of the major groups are provided. Microbiology came into being largely through studies of bacteria.

Microorganims are widespread in nature and are beneficial to life, but some can cause serious harm. They can be divided into six major types: bacteria, archaea, fungi, protozoa, algae, and viruses. Bacteria are unicellular organisms.