TAXONOMY: cellular organisms -> Bacteria -> Terrabacteria group -> Tenericutes -> Mollicutes
The 'Mollicutes' are a class of bacteria distinguished by the absence of a cell wall. The word 'Mollicutes' is derived from the Latin mollis (meaning 'soft' or 'pliable'), and cutis (meaning 'skin'). Individuals are very small, typically only 0.2–0.3 μm in size and have a very small genome size. They vary in form, although most have sterols that make the cell membrane somewhat more rigid. Many are able to move about through gliding, but members of the genus Spiroplasma are helical and move by twisting. The best-known genus in Mollicutes is Mycoplasma. Mollicutes are parasites of various animals and plants, living on or in the host's cells. Many cause diseases in humans, attaching to cells in the respiratory or urogenital tracts, particularly species of Mycoplasma and Ureaplasma urealyticum Ureaplasma. Phytoplasma and Spiroplasma are plant pathogens associated with insect vectors. Whereas formerly the trivial name 'mycoplasma' has commonly denoted any member of the class Mollicutes, it now refers exclusively to a member of the genus Mycoplasma. The Western diet increased the relative abundance of Firmicutes due to a bloom in the class of Mollicutes at the expense of the Bacteriodetes, inducing an enrichment in genes enabling energy harvest from the diet.