‘Microbial diversity’ considers the vast array of microorganisms—the smallest forms of life—which exist everywhere. The three primary groups of microorganisms are bacteria, archaea, and eukaryotes. Bacteria and archaea are prokaryotes with their genetic material held in a single chromosome. In eukaryotes, most of the genome is held in multiple chromosomes. Over 11,000 species of bacteria have been identified using microscopic identification of cell shape and metabolic activity, Gram-staining techniques, and genetic identification of RNA and DNA sequences. There are 500 named species of archaea, divided into two phyla: the euryarchaeota and the crenarchaeota. There are eight supergroupings of eukaryotes, all of them include single-celled organisms, and five are entirely microbial.