Here, we want to determine whether indole plays a more important role in the metabolic pathway or as a quorum sensing signal. For this, metabolic flux analysis of the tryptophan metabolic pathway was performed fixing the extracellular indole flux and synthesis of indole flux, and using two objective functions: minimization of redox potential and maximization of Acetyl-CoA flux. It was established that both, indole flux and synthesis of indole have a positive effect over the Acetyl-CoA flux, moreover, we found the cell finds it more efficient to minimize the use of energy rather than produce more of it; from which it is concluded that the best objective function for this system is the minimization of the redox potential. At high cell density and starving conditions cells minimize redox potential in order to decrease the number of oxidizing reactions that occur thus conserving its energy or using its energy in the most efficient way possible. It was proved that indole plays a more important role as a quorum sensing signal than it does in the cell metabolism; which was shown by the sensibility analysis.
Finally the phase diagram was constructed by calculating the shadow price for the redox potential over the concentration of extracellular indole. The diagram showed tree different zones: a irregular zone in which the shadow prize shows no tendency over a change in extracellular indole or extracellular indole; a second zone where the shadow price decreases to a minimum value; and the third zone in which the shadow price exhibit a regular tendency creating a plane figure.