Which groups of microorganisms are studied in microbiology?

Microbiology is the scientific study of microorganisms—organisms that are generally too small to be seen without the aid of a microscope. The field encompasses several major groups of microorganisms, including:12

• Bacteria: Single-celled prokaryotic organisms that lack a membrane-bound nucleus.3
• Archaea: Prokaryotes that are distinct from true bacteria in their chemical composition and biochemical activities; many are known as extremophiles due to their ability to survive in harsh environments.3
• Fungi: A group that includes yeasts and molds.4
• Algae: Diverse photosynthetic organisms.42
• Protozoa: A group of eukaryotic microorganisms.42
• Viruses: Infectious agents that exist on the borderline of living organisms and are studied in the field of virology.5
• Prions: The simplest infectious agents, consisting of self-perpetuating proteins that lack genetic material.6

While these are the primary groups, the term "microbe" is broad and can sometimes include other tiny organisms, such as certain worms or rotifers.2