Characterization of Escherichia coli Alkaline Phosphatase Response to Osmotic Stress Conditions in Limited and Rich Media

Abstract

The pho regulon in Escherichia coli responds to osmotic stress. Previous studies indicated that in nutrient limited medium, expression of phoA, one gene of the pho regulon, increased as the osmolarity increased. By contrast, in nutrient complex medium, phoA expression was not directly proportional to osmolarity. In this experiment, the effect of supplementing nutrient-limited medium with either glutamate or proline was characterized to test the hypothesis that osmoprotectants in nutrient-complex medium may avert induction of phoA expression. Compared to nutrient-limited conditions, lower alkaline phosphatase specific activity was detected under nutrient rich condition suggesting the presence of osmoprotectants in the nutrient-rich medium. Our results suggest that, in addition to intended osmotic stress, starvation was unexpectedly induced. Consequently, conclusive results were difficult to deduce.