Question

In regards to Simmon's Citrate Agar, how does a cell use ammonium, and by what pathway does a cell use citric acid?

Answer 1

Simmon's citrate agar contains the sodium citrate as a source of carbon , ammonium dihydrogen phosphate as a source of nitrogen and bromthymol blue as pH indiccator.

Simmon's citrate agar, on the basis of citrate utilization dfferentiates the gram negative bacteria. It is a diffferential and selective medium that differentiate the organisms that uses citrate as an energy source and ammonium ions as a nitrogen source.

Organisms that has citrate permease or citrase for transport of citrate into the cell can utilize the citrate as an energy source and that organisms which can utilize ammonia as a nitrogen source can convert ammonium dihydrogen phosphate into ammonia and ammonia hydroxide. Increase in ammonia causes, ammonia to combine with water to form NH₄OH that causes the increase in the pH and results in the development of alkaline media and at pH 7.5 or above the bromthymol blue (i.e pH indicator) can turns into blue.

Pathway that are involved in citric acid utilization are :

First bacteria's citrate permease or citrase converts citrate into the pyruvate and this pyruvate further enters into the metabolic pathways that involved in the generation of energy. Citrate can also be utilize as an intermediate in the kreb's cycle.