Ureaplasma Urease Genes have Undergone a Unique Evolutionary Process

Abstract

Ureaplasma, a member of mycoplasmas, has a unique ATP synthesis system, which is coupled to the urea hy- drolysis. Urease catalyzes the hydrolysis of urea into carbon dioxide and ammonia. Phylogenetic analyses of the urease genes indicated that Ureaplasma urease genes were not gained by recent horizontal transfer and have a unique evolution- ary process. Ureaplasma unique ATP synthesis system leaded to breakdown of the glycolysis pathway. Some glycolytic genes are absent and some glycolytic genes are evolving under relaxed selection in Ureaplasma. Probably glycolytic genes can be used as an indicator of ATP synthesis system. Thus, the organisms that have incomplete glycolysis pathway or glycolytic genes evolving under relaxed selection would have an ATP synthesis system independently of the glycolysis. Mycoplasmas are widespread in nature as parasites of mammals, reptiles, fishes, arthropods, and plants (1). During the mycoplasma evolution, gene loss has occurred fre- quently, resulting in very small genome size (1-3). The re- ductive evolution of mycoplasmas is still in progress. The genus Ureaplasma is a member of mycoplasmas, which gen- erates 95% of its ATP using the hydrolysis of urea (4). Growth of Ureaplasma is dependent on urea (5). This unique ATP synthesis is not found in the other mycoplasmas. In fact, key enzymes in the glycolytic pathway are absent in Ureaplasma (6). In addition, some glycolytic genes of Urea- plasma are evolving under relaxed selection (7, 8). Thus, the glycolysis pathway is collapsing in Ureaplasma.