Mycoplasmosis and immunity of fish and reptiles.

Advances in molecular phylogenetics have enabled reconstruction of the most likely chronology of events in prokaryotic evolution and correlation with the paleontologic record with increasing precision. Mycoplasmas probably evolved from clostridial ancestors by genome reduction leading to obligate parasitism of host cells. The vertebrate hosts present at the time of the origin of mycoplasmas about 400 million years ago were fish, and later amphibians and reptiles, whose descendants possess most elements of vertebrate innate and adaptive immunity. Successful colonization of those poikilothermous ("cold-blooded") hosts must have involved adaptation to those defenses, shaping mycoplasma-host interactions for more than 125 million years before the earliest emergence of mammals. That history illuminates one aspect of the potential significance of mycoplasmosis of poikilothermous vertebrates to health and disease of other hosts including humans.