Glossary of Terms Frequently Used in the Database microorganism
or microbe is an organism that is microscopic (too small to be
visible to the human eye). The study of microorganisms is called
microbiology. Microorganisms can be bacteria, fungi, archaea or
protists, but not viruses and prions because they are generally
classified as non-living (though database includes them also) .
Micro-organisms are often described as single-celled, or
unicellular organisms; however, some unicellular protists are
visible to the human eye, and some multicellular species are
microscopic. Microorganisms live almost everywhere on earth
where there is liquid water, including hot springs on the ocean
floor and deep inside rocks within the earth's crust.
Microorganisms are critical to nutrient recycling in ecosystems
as they act as decomposers. As some microorganisms can also fix
nitrogen, they are an important part of the nitrogen cycle.
However, pathogenic microbes can invade other organisms and
therefore cause disease. An antige