(601a) Is It Indole Language or Food? Phase Plane Analysis of Indole as Quorum Sensing Signal in E. Coli

Indole is a stationary phase signal secreted by Escherichia coli and has been shown to have two important roles: quorum sensing signal that reduces biofilm formation and metabolic reporter that regulates several genes expression (e.g., astD, tnaB, gabT). Nevertheless, the main function that carries out indole in E. coli has not been clearly elucidated. Here we evaluate its role through computational and experimental techniques utilizing Flux-balance analysis (FBA) model to determine metabolites flux distribution relying on metabolic reactions stoichiometry, limited substrates availability and optimality principles. We found that synthesis and exchange fluxes which maximize the biomass production were 24.6 and 2.64 mM/h g cell, respectively. The shadow prices vector was calculated to study the biomass objective function sensibility to finally obtain a phenotype phase plane. In order to validate the plane obtained we evaluated biofilm formation in 96-well plates and cellular growth at different exchange and synthesis flux of indole by increasing extracellular indole concentration or modifying E. coli indole flux synthesis with E. coli K-12 pCA24N tnaA+. The indole synthesis process displays a stronger impact than exchange process on metabolic state of E. coli. So we conclude that indole in E. coli displays a role as metabolic state probe rather than quorum sensing signal.