Factors Determining the Viability of Selected Microorganisms in Inorganic Media

The viability of five selected species of mi-croorgansms i simple, inorganic media was investigated in order to find a basal medium suit-able for a comparative series of irradiation experi-ments. The nature of the studies required that the medium mantain a constant viable count for at least three hours at 20 to 25 C, induce only minimal metabolic activity, be of a simple, re-producible composition, be suitable for a variety of species, and involve only solutes that are practically inert radiochemically. It seemed likely that phosphate buffer would be satisfactory. However, little is known about the survival of microorganisms in this medium, perhaps as a result of the attitude of early in-vestigators of microbial metabolism. For example, Quastel (1928) pointed out that respiration per-sisted long after the ability to reproduce was lost and suggested that viability was of no conse-quence in most metabolic studies. The suitability of phosphate buffer as a diluent for water analysis was investigated by Butter-field (1933), using river water samples with their natural, mixed populations as the test material. Phosphate buffer, with or without the addition of CaCl2, MgSO4, and FeCl1, gave much better survival and more consistent results than distilled water or autoclaved bicarbonate solution. The survival of Eswherichia coli in solutions