GROWTH AND SURVIVAL OF ESCHERICHIA COLI IN MEDIUM LIMITED IN PHOSPHATE

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Abstract
Washed suspensions of Escherichia coli B increased in turbidity and plate count when incubated at 36.5 to 38[degree]C without added phosphate. The population increased more quickly than did the turbidity. On continued incubation, cell viability decreased rapidly in the presence of all necessary nutrients except phosphate. The decline in viability was logarithmic for 90% of the death curve, suggesting loss of a single critical process. Various combinations of phosphate-starved cells and log-phase cells with fresh, phosphate-deficient and phosphate-containing media, and medium depleted of any contaminating phosphate suggested that the simple, phosphate-deficient medium was, in fact, devoid of available phosphorus. This deduction was confirmed by the linearity and extrapolation through the origin of a plot of turbidity against inoculum size. Cell suspensions increased in a linear manner, with the phosphate concentration at low levels. Therefore, a threshold requirement of phosphate for growth of E. coli did not exist, at least, above 1 x 10-9 moles of phosphate per ml. Thus, there is no mainten-ance level for phosphorus in the organism analogous to the energy of maintenance. When cells had been previously incubated without exoge-nous phosphate, their subsequent response to added phosphate was limited. Moderate additions of phosphate did not raise the turbidity much above a plateau value reached at lower phosphate concentrations. Under such conditions, the cells were still viable as measured by plate counting. Yet, when returned to a relatively complete but simple medium after starvation, they could not divide normally. Growth of E. coli in a medium deficient only in phosphate rendered the cells susceptible to death on continued incubation. Apparently, material lost during starvation was necessary for multiplication. It was replaced by the plating medium and colonies formed.

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