Physiology of Mycoplasmas

Abstract

The chapter focuses on the physiology of Mycoplasmas. The physiology of mycoplasmas, the smallest organisms capable of autonomous growth, is of special interest in view of their extremely simple structure and limited biochemical activities. Because of the recent improvements in cultivation and identification techniques, quite a number of further mycoplasma species could be established. By now, over 40 species occurring in primates, farm and laboratory animals, and a variety of wild animals have been named. In the absence of a cell wall, the mycoplasmas are so fragile and pliable that their morphology was long disputed. Mycoplasma can grow in filaments; the different strains vary in their ability to do so. This may be due to the differences in their ability to synthesize certain membrane components, when the supply of precursors in the growth medium is limited. The extremely simple ultrastructure found in numerous electron microscope studies of thin mycoplasma sections supports the view that they are the simplest and the most primitive organisms extant. Essentially, the mycoplasma cell is built of only three organelles: the cell membrane, the ribosome, and the characteristic prokaryotic chromosome. Though the unusual physiological properties of the new Thermoplasma acidophilum suggest a rather distant relationship to the animal mycoplasmas, its inclusion in the Mollicutes class seems warranted, and its very existence considerably broadens the range of habitats in which mycoplasma-like organisms are found.