The complete sequence of the mucosal pathogen Ureaplasma urealyticum

The comparison of the genomes of two very closely related human mucosal pat hogens, Mycoplasma genitalium and Mycoplasma pneumoniae, has helped define the essential functions of a self-replicating minimal cell, as well as what constitutes a mycoplasma. Here we report the complete sequence of a more d istant phylogenetic relative of those bacteria, Ureaplasma urealyticum (par vum biovar), which is also a mucosal pathogen of humans. It is the third my coplasma to be sequenced, and has the smallest sequenced prokaryotic genome except for M. genitalium. Although the U. urealyticum genome is similar to the two sequenced mycoplasma genomes(1,2), features make this organism uni que among mycoplasmas and all bacteria. Almost all ATP synthesis is the res ult of urea hydrolysis, which generates an energy-producing electrochemical gradient. Some highly conserved eubacterial enzymes appear not to be encod ed by U. urealyticum, including the cell-division protein FtsZ, chaperonins GroES and GroEL, and ribonucleoside-diphosphate reductase. U. urealyticum has six closely related iron transporters, which apparently arose through g ene duplication, suggesting that it has a kind of respiration system not pr esent in other small genome bacteria The genome is only 25.5% G+C in nucleo tide content, and the G+C content of individual genes may predict how essen tial those genes are to ureaplasma survival.