SOME RADIOBIOLOGICAL CONSEQUENCES OF MYCOPLASMA CONTAMINATION OF MAMMALIAN-CELLS IN TISSUE-CULTURE

Cells of the mouse Ehrlich ascites carcinoma grown in vitro became contaminated with an arginine-splitting mycoplasma. The slopes of the radiation dose-survival curves of the contaminated cells, assayed by colony-forming ability, were extremely variable; eventually it became impossible to grow colonies at all. Experiments on the feeder cell requirement showed that, whereas for clean cells the maximum plating efficiency was obtained within a range of 5 x 104 and 4 x 105 feeder cells in a 5cm dish, contaminated cells would only produce colonies in the presence of between 104 and 3 x 104 feeder cells. Doubling the concentration of arginine in the medium allowed contaminated cells to grow with maximum plating efficiency within an increased range of 104 and 4 x 105 feeder cells. The mycoplasmas were apparently behaving as feeders, reducing the requirement for added feeder cells, but also depleting the medium of essential arginine. The cells were eventually decontaminated by passing them through a mouse as an ascites tumour.